Marjoram extract prevents ischemia reperfusion-induced myocardial damage and exerts anti-contractile effects in aorta segments of male wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

Marjoram (Origanum majorana L.) is an herb traditionally used as a medicine in different countries, as Morocco and Iran, because of its beneficial cardiovascular effects. Some studies suggest that these effects are due, at least in part, to the presence of phenolic compounds such as rosmarinic acid (RA) and luteolin.

AIM OF THE STUDY

To analyze the possible cardiprotective effects of a marjoram extract (ME) reducing myocardial damage after coronary ischemia-reperfusion (IR) and its possible antihypertensive effects reducing the response of aorta segments to the vasoconstrictors noradrenaline (NA) and endothelin-1 (ET-1).

MATERIALS AND METHODS

Male Wistar rats (300g) were used. After sacrifice, the heart was immediately removed and mounted in a perfusion system (Langendorff). The aorta was carefully dissected and cut in 2 mm segments to perform vascular reactivity experiments.

RESULTS

In the heart, ME perfusion after IR reduced heart rate and prevented IR-induced decrease of cardiac contractility, possibly through vasodilation of coronary arteries and through the upregulation of antioxidant markers in the myocardium that led to reduced apoptosis of cardiomyocytes. In the aorta, ME decreased the vasoconstrictor response to NA and ET-1 and exerted a potent anti-inflammatory and antioxidant effect. Neither RA nor 6-hydroxi-luteolin-O-glucoside, major compounds of this ME, were effective in improving cardiac contractility after IR or attenuating vasoconstriction to NA and ET-1 in aorta segments.

CONCLUSION

In conclusion, ME reduces the myocardial damage induced by IR and the contractile response to vasoconstrictors in the aorta. Thus, it may be useful for the treatment of cardiovascular diseases such as myocardial infarction and hypertension.

Study of insulin vascular sensitivity in aortic rings and endothelial cells from aged rats subjected to caloric restriction: Role of perivascular adipose tissue

The prevalence of metabolic syndrome is dramatically increasing among elderly population. Metabolic syndrome in aged individuals is associated with hyperinsulinemia and insulin resistance both in metabolic tissues and in the cardiovascular system, with this fact being associated with the cardiometabolic alterations associated to this condition. Caloric restriction (CR) improves insulin sensitivity and is one of the dietetic strategies most commonly used to enlarge life and to prevent aging induced cardiovascular alterations. The aim of this study was to analyze the possible beneficial effects of CR in aging-induced vascular insulin resistance both in aortic rings and in primary culture of endothelial cells. In addition, the inflammatory profile of perivascular adipose tissue (PVAT) and its possible role in the impairment of vascular insulin sensitivity associated with aging was also assessed. Three experimental groups of male Wistar rats were used: 3 (3m), 24 (24m) fed ad libitum and 24months old rats subjected to 20% CR during their three last months of life (24m-CR). Aorta rings surrounded or not by PVAT were mounted in an organ bath and precontracted with phenylephrine (10^-7.5M). Changes in isometric tension were recorded in response to cumulative insulin concentrations (10^-8-10^-5.5M) in the presence or absence of L-NAME (10^-4M). Aortic rings and primary aortic endothelial cells were incubated in presence/absence of insulin (10^-7M) and the activation of the PI3K/Akt and MAPK pathways as well as nitrite and nitrates concentrations and the mRNA levels of eNOS, insulin receptor, and GLUT-4 were assessed. CR prevented the aging-induced decrease in the vasodilator response to insulin and the aging-induced increase in the vasoconstrictor response to high insulin concentrations. Changes between 24m and 24m-CR aorta rings were abolished in the presence of L-NAME. CR induced-improvement in insulin vascular sensitivity was related with activation of the PI3K/Akt both in aortic rings and in aortic endothelial cells in response to insulin. CR attenuated the overexpression of iNOS, TNF-α and IL-1β in the PVAT of aged rats although aortic rings surrounded by PVAT from 24m rats showed and increased vasorelaxation in response to insulin compared to aortic rings from 3m and 24m-CR rats. In conclusion, a moderate protocol of CR improves insulin vascular sensitivity and prevents the aging induced overexpression of pro-inflammatory cytokines in PVAT.

Effects of early overnutrition on the renal response to Ang II and expression of RAAS components in rat renal tissue

BACKGROUND AND AIMS

The aim of this study was to analyze the effects of early overnutrition (EON) on the expression of the renin angiotensin aldosterone system (RAAS) components in renal cortex, renal arteries and renal perivascular adipose tissue (PVAT), as well as the vascular response of renal arteries to Angiotensin II (Ang II).

METHODS AND RESULTS

On birth day litters were adjusted to twelve (L12-control) or three (L3-overfed) pups per mother. Half of the animals were sacrificed at weaning (21 days old) and the other half at 5 months of age. Ang II-induced vasoconstriction of renal artery segments increased in young overfed rats and decreased in adult overfed rats. EON decreased the gene expression of angiotensinogen (Agt), Ang II receptors AT1 and AT2 and eNOS in renal arteries of young rats, while it increased the mRNA levels of AT-2 and ET-1 in adult rats. In renal PVAT EON up-regulated the gene expression of COX-2 and TNF-α in young rats and the mRNA levels of renin receptor both in young and in adult rats. On the contrary, Ang II receptors mRNA levels were downregulated at both ages. Renal cortex of overfed rats showed increased gene expression of Agt in adult rats and of AT1 in young rats. However the mRNA levels of AT1 were decreased in the renal cortex of overfed adult rats.

CONCLUSION

EON is associated with alterations in the vascular response of renal arteries to Ang II and changes in the gene expression of RAAS components in renal tissue.

Peritumoral adipose tissue as a source of inflammatory and angiogenic factors in colorectal cancer

PURPOSE

Obesity is a risk factor for the development of human colorectal cancer (CC). The aim of this work is to report the inflammatory and angiogenic scenario in lean (BMI < 25 kg/m2) and obese (BMI > 30 kg/m2) patients with and without CC and to assess the role of peritumoral adipose tissue in CC-induced inflammation.

MATERIAL AND METHODS

Patients were divided in four experimental groups: obese patients with CC (OB-CC), lean patients with CC (LEAN-CC), obese patients without CC (OB), and lean patients without CC (LEAN).

RESULTS

Plasma levels of pro-inflammatory cytokines (interleukin (IL)-6, IL-4, IL-8) and granulocyte-macrophage colony-stimulating factor (GM-CSF) were increased in OB-CC patients. Peritumoral adipose tissue (TF) explants and cultured mature adipocytes secreted higher amounts of nitrites and nitrates than did control and non-tumoral (NTF) adipose tissue both alone and in response to lipopolysaccharide (LPS). Nitrite and nitrate secretion was also increased in TF explants from OB-CC patients compared with that from LEAN-CC patients. Gene expression of adiponectin, tumor necrosis factor alpha (TNF-α), insulin-like growth factor type I (IGF-I), cyclooxygenase-2 (COX-2), and peroxisome proliferator-activated receptor γ (PPAR-γ) was increased in TF explants from CC patients. LPS increased the gene expression of IL-6, IL-10, TNF-α, vascular endothelial growth factor (VEGF), and COX-2 in OB and in TF explants from OB-CC patients. COX-2 and PPAR-γ inhibition further increased LPS-induced release of nitrites and nitrates in TF explants and adipocytes from OB-CC patients.

CONCLUSIONS

In conclusion, OB-CC patients have increased plasma levels of pro-inflammatory and angiogenic factors. TF from OB-CC patients shows an increased secretion of inflammatory markers compared with both TF from LEAN-CC and non-tumoral adipose tissue (AT) through a COX-2- and PPAR-γ-independent mechanism.

Response of Rabbit Ear and Femoral Arteries to 5-Hydroxytryptamine During Cooling

The effects of cooling on the response of cutaneous and non-cutaneous arteries to 5-hydroxytryptamine (5-HT) were analysed.

Segments 2-mm long from rabbit central ear (cutaneous) and femoral (non-cutaneous) arteries were prepared for isometric tension recording in an organ bath at 37 and 24°C (cooling). 5-HT (10−9-3 times 10−4 M) induced concentration-dependent contraction of the arteries. The sensitivity and maximal contraction of ear arteries and only the maximal contraction of femoral arteries to this amine were reduced at 24°C.

Endothelium removal or pretreatment with the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 10−5  m) did not affect the response at 37°C but reversed the decreased sensitivity at 24°C in ear arteries, and neither procedure modified the reactivity at 24 or 37°C in femoral arteries to 5-HT. At both temperatures, the response of ear arteries to 5-HT was shifted to the right by phentolamine (10−6M) more than by the 5-HT antagonist, ketanserin (3 times 10−7M), and that of femoral arteries was shifted to the right by ketanserin or the 5-HT1/5-HT2 antagonist methysergide (3 times 10−7 M) more than by phentolamine, in arteries with and without endothelium.

These data concur with the proposition that the contraction to 5-HT is mediated mainly by α-adrenergic receptors in ear arteries and mainly by 5-HT-ergic receptors in femoral arteries, and suggest that cooling reduces the sensitivity of cutaneous, but not of deep arteries to 5-HT, probably by endothelium-nitric oxide-dependent mechanisms.

Coronary reactive hyperaemia and arterial pressure in anaesthetized goats

To study the effects of arterial pressure on coronary reactive hyperaemia, left circumflex coronary artery flow was measured, and reactive hyperaemia was determined after 5, 10 or 20 s of occlusion of this artery in anaesthetized goats during normotension, hypertension and hypotension. During hypertension induced by aortic constriction (mean arterial pressure, MAP = 140 +/- 6 mmHg) coronary vascular resistance (CVR), reactive hyperaemia (ratio of peak in hyperaemic flow to control flow and ratio of repayment to debt) and the decrease in CVR during the peak in hyperaemic flow were comparable to those during normotension. During hypertension induced by noradrenaline (MAP = 144 +/- 6 mmHg) CVR was 16% lower (P < 0.05), reactive hyperaemia was reduced by 14-25% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was lower than the values of these parameters during normotension. During hypotension induced by constriction of the caudal vena cava (MAP = 40 +/- 4 mmHg) CVR was 22% lower (P < 0.05), reactive hyperaemia was reduced by 25-65% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. During hypotension induced by isoprenaline (MAP = 45 +/- 4 mmHg) CVR was 59% lower, reactive hyperaemia was reduced by 55-100% (P < 0.01) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. Arterial pressure is a main determinant of coronary reactive hyperaemia after brief periods of ischaemia, and the relationship between arterial pressure and reactive hyperaemia may depend in part on changes in CVR after variations in arterial pressure. These changes in CVR may be related to the action on coronary vessels of myocardial factors and vascular myogenic mechanisms.

Diabetes abolishes the gender difference in vasopressin-mediated potentiation of sympathetic vasoconstriction

Electrical field stimulation (4 Hz, 0.2 ms pulse duration, at a supramaximal voltage of 70 V, for 1 s) of isolated rat tail artery segments produced contraction which was lower in female than in male rats, and was reduced by streptozotocin-induced diabetes in both genders. This contraction was potentiated by vasopressin (10(-12)-10(-10) M) more in normoglycemic male than in normoglycemic female rats, and this effect of vasopressin was increased by the cyclooxigenase inhibitor meclofenamate (10(-5) M) in female control rats, but not in diabetic female, or control and diabetic male rats, and it was not modified by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 10(-4) M). Endothelin-1 (10(-10)-3 x 10(-9) M) also potentiated the contraction to electrical stimulation. This potentiation was similar in all experimental groups, and it was not modified by meclofenamate or L-NAME. These results suggest that the potentiating effect of vasopressin, but not that of endothelin-1, on the sympathetic vasoconstriction, is lower in females than in males, probably by an increased release of vasodilating prostanoids, and this release may be reduced by diabetes in females.

Adrenergic vasoconstrictor activity in the cerebral circulation after inhibition of nitric oxide synthesis in conscious goats

The interaction between nitric oxide (NO) and adrenergic activity in the cerebral circulation was studied using conscious goats, where blood flow to one brain hemisphere (cerebral blood flow) was electromagnetically measured, and the effects of phentolamine and hexamethonium on cerebrovascular resistance were evaluated before (control) and after inhibition of NO synthesis with NW-nitro-L-arginine methyl ester (L-NAME). L-NAME (12 goats, 40 mg kg(-1) administered i.v.) reduced cerebral blood flow from 62 +/- 3 to 44 +/- 2 ml min(-1), increased mean systemic arterial pressure from 100 +/- 3 to 126 +/- 4 mm Hg, decreased heart rate from 79 +/- 5 to 50 +/- 4 beats min(-1) and increased cerebrovascular resistance from 1.63 +/- 0.08 to 2.91 +/- 0.016 mm Hg ml(-1)min(-1) (all P < 0.01). These hemodynamic variables normalized 48-72 h after L-NAME administration. Phentolamine (six goats, 1 mg), injected into the cerebral circulation. increased cerebral blood flow without changing systenic arterial pressure, but its cerebrovascular effects were augmented for about 24 h after L-NAME. The decrements in cerebrovascular resistance induced by phentolamine, in mm Hg ml(-1) min(-1), were: under control, 0.42 +/- 0.05; immediately after L-NAME, 1.38 +/- 0.09 (P < 0.01 compared with control); by about 24 h after L-NAME, 0.71 +/- 0.09 (P < 0.05 compared with control); and by about 48 h after L-NAME, 0.40 +/- 0.07 (P > 0.05 compared with control). Hexamethonium (six goats, 0.5-1 mg kg(-1) min(-1) i.v.) decreased mean systemic arterial pressure to about 75 mm Hg and caused tachycardia similarly before and after L-NAME, but the decrements in cerebrovascular resistance were augmented for about 24 h after L-NAME. The decrements in cerebrovascular resistance induced by hexamethonium, in mm Hg ml(-1).min(-1), were: under control. 0.61 +/- 0.09, immediately after L-NAME, 1.33 +/- 0.16 (P < 0.01 compared with control); by about 24 h after L-NAME, 1.18 +/- 0.10 (P < 0.01 compared with control): and by about 48 h after L-NAME, 0.99 +/- 0.10 (P > 0.05 compared with control). Therefore, these results suggest that adrenergic vasoconstrictor tone in cerebral vasculature may be augmented after inhibition of NO synthesis, and that this increment may contribute to the reduction of cerebral blood flow after inhibition of NO formation.

Cerebral vasoconstriction produced by vasopressin in conscious goats: role of vasopressin V(1) and V(2) receptors and nitric oxide

To examine the role of vasopressin V(1) and V(2) receptors, nitric oxide and prostanoids in the cerebrovascular effects of arginine vasopressin, cerebral blood flow was electromagnetically measured in awake goats. In 16 animals, vasopressin (0.03 - 1 microg), injected into the cerebral circulation, caused increments of resting cerebrovascular resistance which ranged from 18% (0.03 microg, P<0.01) to 79% (1 microg, P<0.01). Desmopressin (0.03 - 1 microg, four goats) did not affect significantly cerebrovascular resistance. The cerebrovascular resistance increases by vasopressin were reduced significantly by the antagonist for vasopressin V(1) receptors d(CH(2))(5)Tyr(Me)-AVP in a rate depending way (five (six goats) and 15 (four goats) microg min(-1)), and by the mixed antagonist for vasopressin V(1) and V(2) receptors desGly-d(CH(2))(5)-D-Tyr(Et)Val-AVP (5 microg min(-1), four goats), and they were not significantly affected by the antagonist for vasopressin V(2) receptors d(CH(2))(5), D-Ile(2), Ile(4)-AVP (5 microg min(-1), four goats). The inhibitor of nitric oxide synthesis N(w)-nitro-L-arginine methyl ester (L-NAME, 47 mg kg(-1) i.v., five goats) augmented cerebrovascular resistance by 130% (P<0.01), and for 24 h after this treatment the cerebrovascular effects of vasopressin were potentiated. The inhibitor of cyclo-oxygenase meclofenamate (6 mg kg(-1) i.v., five goats) did not modify significantly resting haemodynamic variables measured or the cerebrovascular effects of vasopressin. Therefore, the vasopressin-induced cerebral vasoconstriction may be mediated by vasopressin V(1) receptors, without involvement of vasopressin V(2) receptors, and may be modulated by nitric oxide but not by prostanoids.

Effect of neuropeptide Y on the sympathetic contraction of the rabbit central ear artery during cooling

In order to analyse the effect of neuropeptide Y (NPY) on the cutaneous vascular response to sympathetic nerve stimulation during cooling, the isometric response of isolated 2-mm segments of the rabbit central ear (cutaneous) artery was recorded at 37 degrees C and during cooling (30 degrees C). Electrical field stimulation (4-16 Hz) at 37 degrees C produced a frequency-dependent contraction, which was reduced during cooling (45% for 16 Hz) and potentiated by NPY (10(-8), 3x10(-8) and 10(-7) M), this potentiation being greater at 30 degrees C than at 37 degrees C. The NPY-induced potentiation of the contraction elicited by electrical field stimulation (8 Hz) was abolished by an antagonist of Y1 subtype NPY receptors, BIBP3226 (10(-6) M), at 37 degrees C and 30 degrees C, reduced by phentolamine (10(-6) M) at 30 degrees C but not at 37 degrees C, was not modified by the purinoceptor antagonist PPADS (3x10(-5) M) and was reduced by application of both phentolamine and PPADS at both temperatures. Both NiCl2 (10(-3) M) and verapamil (10(-5) M) abolished the potentiating effect of NPY at 37 degrees C and reduced it at 30 degrees C. Neither application of an inhibitor of nitric oxide synthesis, L-Nomega-nitro-arginine (L-NOARG, 10(-4) M), nor endothelium removal modified the potentiating effect of NPY at 37 degrees C or 30 degrees C. NPY (10(-8), 3x10(-8) and 10(-7) M) potentiated in a concentration-dependent way the arterial contraction in response to exogenous noradrenaline (10(-8)-10(-4) M) at 30 degrees C but not at 37 degrees C, and it increased the response to ATP (10(-4)-10(-2) M) at both temperatures. Therefore, in cutaneous (ear) arteries: (1) NPY potentiates the sympathetic response at 37 degrees C and at 30 degrees C, (2) this potentiating effect of NPY was more marked at 30 degrees C than at 37 degrees C, probably because of greater potentiation of the alpha-adrenoceptor response during cooling, and (3) the potentiating effect of NPY at both temperatures is mediated by NPY receptors of the Y1 subtype, is dependent of Ca2+ channels and is independent of the release of endothelial nitric oxide.

Insulin effects on the sympathetic contraction of rabbit ear arteries

Electrical field stimulation (4 Hz, 0.2 ms, 70 V supramaximal voltage, 10 s duration) produced contraction of perfused rabbit central ear arteries, and this contraction was reduced by incubation with insulin (0.6--200 mU/ml). This inhibitory effect of insulin was not significantly modified by removing the endothelium, or by treatment with N(W)-nitro-L-arginine (L-NA, 10(-4) M), meclofenamate (10(-5) M), ouabain (10(-6) M), or cocaine (10(-5) M). Insulin (200 mU/ml) did not modify the vascular contraction due to exogenous norepinephrine (10(-8)--10(-4) M) nor the relaxation due to acetylcholine (10(-8)--10(-4) M). This suggests that insulin may reduce vascular contraction by sympathetic stimulation, and this effect is not dependent on endothelial nitric oxide, prostanoids, or Na(+)--K(+) pump activation.

Impaired potentiation by endothelin-1 and vasopressin of sympathetic contraction in tail artery from hypertensive rats

OBJECTIVE

To analyse the effects of endothelin-1 and vasopressin on the sympathetic vasoconstriction during hypertension.

METHODS

Electrical field stimulation (4 Hz) was applied to isolated, 2 mm segments of the tail artery from spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats prepared for isometric tension recording.

RESULTS

The contraction to electrical stimulation was potentiated by endothelin-1 (10(-10)-10(-8) M) in arteries from WKY but not from SHR, and by vasopressin (10(-12)-10(-10) M) more markedly in arteries from WKY than from SHR. The potentiation by endothelin-1 was reduced more markedly by the antagonist of endothelin ETA receptors BQ-123 (10(-5) M) than by the endothelin ETB receptor antagonist BQ-788 (10(-5) M). The potentiation by vasopressin was reduced by the antagonist of vasopressin V1 receptors d(CH2)5Tyr(Me)AVP (10(-7) M), but not by the vasopressin V2 receptor antagonist d(CH2)5D-Ile2, Ile4AVP (10(-7) M). The blocker of L-type calcium channels verapamil (10(-5) M) reduced the potentiation by both endothelin-1 and vasopressin in arteries from WKY rats, and increased the potentiation by vasopressin in arteries from SHR. Noradrenaline (10(-8)-10(-4) M) contraction was not modified by endothelin-1 (3 x 10(-9) M) or vasopressin (3 x 10(-11) M), and contraction to endothelin-1 (10(-9)-10(-7) M) and vasopressin (10(-10)-10(-7) M) was lower in arteries from SHR than from WKY rats.

CONCLUSIONS

(1) The potentiation by endothelin-1 and vasopressin of the sympathetic vasoconstriction, probably due to increased release of noradrenaline, is impaired during hypertension, and (2) this potentiation is mediated mainly by endothelin ETA receptors, and by vasopressin V1 receptors, in both WKY and SHR, and for both peptides it is mediated by L-type calcium channels in arteries from normotensive but not in those from hypertensive animals.

Role of nitric oxide in vascular tone and in reactivity to isoproterenol and adenosine in the goat coronary circulation

The present study examined the role of nitric oxide in coronary vascular tone and in the coronary vasodilatation in response to beta-adrenoceptor stimulation and adenosine. In anesthetized goats, the effects of intracoronary and i.v. administration of the inhibitor of nitric oxide synthesis, N(w)-nitro-L-arginine methyl ester (L-NAME), and those of isoproterenol, adenosine and acetylcholine on coronary blood flow, measured electromagnetically in the left circumflex coronary artery, were recorded. Intracoronary infusion of L-NAME (30-40 microg kg(-1) min(-1), four goats) reduced resting coronary blood flow by 14+/-3% (P<0.05) without changing arterial pressure and heart rate. L-NAME (40 mg kg(-1), eight goats) i.v. reduced resting coronary blood flow by 19+/-4% (P<0.05), increased mean systemic arterial pressure by 22+/-3% (P<0.01) and decreased heart rate by 10+/-2% (P<0.05). These effects of L-NAME were partially, but significantly reversed by L-arginine (six goats). Isoproterenol (10-100 ng, eight goats), adenosine (0.3-10 microg, seven goats) and acetylcholine (3-100 ng, five goats), injected intracoronarily, increased coronary conductance in a dose-dependent way and, under control conditions, these increases for isoproterenol, ranged from 32+/-5% to 82+/-12%; for adenosine, 6+/-2% to 174+/-22%; and for acetylcholine, 39+/-5% to 145+/-15%. During i.v. L-NAME the increases in coronary conductance induced by isoproterenol and acetylcholine were significantly reduced by about 50 and 60% (P<0.05), respectively, whereas those induced by adenosine were significantly increased further (about 30-100%, P<0. 05). During L-NAME plus L-arginine, the effects of isoproterenol, acetylcholine and adenosine on coronary conductance were not significantly different from those under control conditions. Therefore, it is suggested that in the coronary circulation: (a) nitric oxide may produce a basal vasodilator tone under normal conditions; (b) nitric oxide may be an intermediate in the vasodilatation due to beta-adrenoceptor stimulation and acetylcholine, and (c) the vasodilatation due to adenosine is potentiated during reduction of nitric oxide production.

Role of nitric oxide in the cerebral circulation during hypotension after hemorrhage, ganglionic blockade and diazoxide in awake goats

The role of nitric oxide in cerebrovascular response to hypotension was analyzed by evaluating the changes in cerebrovascular resistance after inhibition of nitric oxide synthesis with Nw-nitro-L-arginine methyl ester (L-NAME) during three types of hypotension in conscious goats. Blood flow to one brain hemisphere was electromagnetically measured, hypotension was induced by controlled bleeding, and by i.v. administration of hexametonium (ganglionic blocker) or of diazoxide (vasodilator drug), and L-NAME was injected by i.v. route (35 mg kg-1). Under control conditions (13 goats), L-NAME increased arterial pressure from 98 +/- 3 to 123 +/- 4 mmHg and decreased cerebral blood flow from 65 +/- 3 to 40 +/- 3 ml min-1 (all P < 0.001); cerebrovascular resistance increased from 1.52 +/- 0.04 to 3.09 +/- 0.013 mmHg ml-1 min-1 (P < 0.01) (delta = 1.59 +/- 0.12 mmHg ml-1 min-1). After bleeding (five goats), mean arterial pressure decreased to 60 +/- 4 mmHg and cerebral blood flow decreased to 37 +/- 4 ml min-1 (all P < 0.01); cerebrovascular resistance did not change (1.56 +/- 0.14 vs. 1.54 +/- 0.12 mmHg ml-1 min-1, P > 0.05). During this hypotension, L-NAME increased arterial pressure to reach the normotensive values an did not affect the hypotensive values for cerebral blood flow; cerebrovascular resistance increased from the hypotensive values to 2.91 +/- 0.19 mmHg ml-1 min-1 (P < 0.01) (delta = 1.37 +/- 0.16 mmHg ml-1 min-1), and this increment is comparable to that under control conditions (P > 0.05). Ganglionic blockade (six goats) decreased arterial pressure to 67 +/- 2 mmHg) and did not affect significantly cerebral blood flow; cerebrovascular resistance decreased from 1.71 +/- 0.11 to 1.05 +/- 0.09 mmHg ml-1 min-1 (P < 0.01). During this hypotension, L-NAME increased arterial pressure to 103 +/- 6 mmHg (P < 0.001), and did not affect cerebral blood flow; cerebrovascular resistance increased from the hypotensive values to 1.68 +/- 0.18 mmHg ml-1 min-1 (P < 0.01) (delta = 0.63 +/- 0.10 mmHg ml-1 min-1), and this increment was lower than under control conditions (P < 0.01). Diazoxide (six goats) decreased arterial pressure to 69 +/- 5 mmHg (P < 0.01) without changing cerebral blood flow; cerebrovascular resistance decreased from 1.89 +/- 0.11 to 1.16 +/- 0.14 mmHg ml-1 min-1 (P < 0.01). During this hypotension, L-NAME increased arterial pressure to 87 +/- 6 mmHg (P < 0.05) and did not affect the hypotensive values for cerebral blood flow (P > 0.05); cerebrovascular resistance increased from the hypotensive values to 1.53 +/- 0.13 mmHg ml-1 min-1 (P < 0.05) (delta = 0.36 +/- 0.06 mmHg-1 ml-1 min-1), and this increment was lower than under control conditions (P < 0.01). Therefore, the role of nitric oxide in cerebrovascular response to hypotension may differ in each type of hypotension, as this role during hemorrhagic hypotension may not change and during hypotension by ganglionic blockade or diazoxide may decrease. These differences may be related to changes in nitric oxide release as stimuli on the endothelium (shear stress and sympathetic activity) may vary in each type of hypotension.

Basal inhibitory action of endogenous endothelin on the sympathetic contraction in the isolated rat tail artery

In order to test whether endogenous endothelin modulates the sympathetic vasoconstriction, arterial segments, 2 mm long, from rat tail artery were mounted in organ baths for isometric tension recording. Electrical field stimulation (2-8 Hz, 0.2 ms, 70 V during 1 s) produced frequency-dependent arterial contraction (maximal contraction 770+/-49 mg) that was nearly abolished (over 95% reduction) by tetrodotoxin (10(-6) M) or phentolamine (10(-6) M). This contraction was increased by pretreatment with the antagonist of endothelin ET(B) receptors N-(N-(N-(2, 6-dimethyl-1-piperidinyl)carbonyl)-4-methyl-L-leucyl)-1-(methoxycarbo nyl)-D-tryptophyl)D-norleucine (BQ-788, 10(-7)-3x10(-6) M), and was not modified either by the antagonist of endothelin ET(A) receptors cyclo(D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl) (BQ-123, 10(-7)-3x10(-6) M) or the agonist of endothelin ET(B) receptors endothelin-1 (8-21), N-Suc-(Glu(9), Ala(11,15)) (IRL-1620, 10(-8)-10(-7) M). The potentiating effect of BQ-788 was not modified in arterial segments without endothelium or pretreated with the inhibitor of nitric oxide synthesis N(W)-nitro-L-arginine (L-NA, 10(-4) M) or with the inhibitor of endothelin converting enzyme N-(alpha-rhamnopyranosyloxy-hydroxyphosphinyl)-leu-trp (phosphoramidon, 10(-4) M). Exogenous noradrenaline (10(-9)-10(-4) M) produced concentration-dependent arterial contractions that were not modified by BQ-788 (3x10(-6) M), BQ-123 (3x10(-6) M) or IRL-1620 (10(-7) M). Therefore, an inhibitory action of endogenous endothelin on sympathetic vasoconstriction may be present under basal conditions. This inhibition could be produced by endothelin through activation of prejunctional endothelin ET(B) receptors, which may inhibit noradrenaline release from perivascular sympathetic nerves.

Effects of vasopressin on the sympathetic contraction of rabbit ear artery during cooling

In order to analyse the effects of arginine-vasopressin on the vascular contraction to sympathetic nerve stimulation during cooling, the isometric response of isolated, 2-mm segments of the rabbit central ear (cutaneous) artery to electrical field stimulation (1-8 Hz) was recorded at 37 and 30 degrees C. Electrical stimulation (37 degrees C) produced frequency-dependent arterial contraction, which was reduced at 30 degrees C and potentiated by vasopressin (10 pM, 100 pM and 1 nM). This potentiation was greater at 30 than at 37 degrees C and was abolished at both temperatures by the antagonist of vasopressin V1 receptors d(CH2)5 Tyr(Me)AVP (100 nM). Desmopressin (1 microM) did not affect the response to electrical stimulation. At 37 degrees C, the vasopressin-induced potentiation was abolished by the purinoceptor antagonist PPADS (30 microM), increased by phentolamine (1 microM) or prazosin (1 microM) and not modified by yohimbine (1 microM), whilst at 30 degrees C, the potentiation was reduced by phentolamine, yohimbine or PPADS, and was not modified by prazosin. The Ca2+-channel blockers, verapamil (10 microM) and NiCl2 (1 mM), abolished the potentiating effects of vasopressin at 37 degrees C whilst verapamil reduced and NiCl2 abolished this potentiation at 30 degrees C. The inhibitor of nitric oxide synthesis, L-NOARG (100 microM), or endothelium removal did not modify the potentiation by vasopressin at 37 and 30 degrees C. Vasopressin also increased the arterial contraction to the alpha2-adrenoceptor agonist BHT-920 (10 microM) and to ATP (2 mM) at 30 and 37 degrees C, but it did not modify the contraction to noradrenaline (1 microM) at either temperature. These results suggest that in cutaneous (ear) arteries, vasopressin potentiaties sympathetic vasoconstriction to a greater extent at 30 than at 37 degrees C by activating vasopressin V1 receptors and Ca2+ channels at both temperatures. At 37 degrees C, the potentiation appears related to activation of the purinoceptor component and, at 30 degrees C, to activation of both purinoceptor and alpha2-adrenoceptor components of the sympathetic response.

Adrenergic reactivity after inhibition of nitric oxide synthesis in the cerebral circulation of awake goats

The interaction between nitric oxide (NO) and adrenergic reactivity in the cerebral circulation was studied using in vivo and in vitro preparations. Blood flow to one brain hemisphere (cerebral blood flow) was electromagnetically measured in conscious goats, and the effects of norepinephrine, tyramine and cervical sympathetic nerve stimulation were recorded before (control) and after inhibition of NO formation with Nw-nitro-l-arginine methyl ester (l-NAME). The responses to norepinephrine, tyramine and electrical field stimulation were also recorded in segments, 4 mm in length, from the goat's middle cerebral artery under control conditions and after l-NAME. In vivo, l-NAME (10 goats, 47 mg kg-1 administered i.v.) reduced resting cerebral blood flow by 37+/-2%, increased mean systemic arterial pressure by 24+/-3%, reduced heart rate by 35+/-2%, and decreased cerebrovascular conductance by 52+/-2% (all P<0.01). Norepinephrine (0.3-9 microgram), tyramine (50-500 microgram), and supramaximal electrical sympathetic cervical nerve stimulation (1. 5-6 Hz) decreased cerebrovascular conductance, and these decreases were significantly higher after l-NAME than under control conditions, remaining higher for about 48 h after this treatment. Norepinephrine (10-8-10-3 M), tyramine (10-6-10-3 M) and electrical field stimulation (1.5-6 Hz) contracted isolated cerebral arteries, and the maximal contraction, but not the sensitivity, was significantly higher in the arteries treated than in non-treated with l-NAME (10-4 M). Therefore, the reactivity of cerebral vasculature to exogenous and endogenous norepinephrine may be increased after inhibition of NO synthesis. This increase might be related, at least in part, to changes at postjunctional level in the adrenergic innervation of the vessel wall, and it might contribute to the observed decreases in resting cerebral blood flow after inhibition of NO synthesis.

Effects of hyperthermia on contraction and dilatation of rabbit femoral arteries

To analyze the effect of hyperthermia on the vascular response, the isometric response of isolated rabbit femoral artery segments was recorded at 37 degreesC and hyperthermia (41 and 44 degreesC). Contraction to potassium (5 x 10(-3)-5 x 10(-2) M) was significantly greater at 41 and 44 than at 37 degreesC and increased by inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine (L-NNA; 10(-4) M) or endothelium removal at 37 degreesC but not at 41 or 44 degreesC. Norepinephrine (10(-9)-10(-4) M) produced a concentration-dependent contraction greater at 41 or 44 than at 37 degreesC and not modified by endothelium removal or L-NNA at either temperature. Phenylephrine (10(-9)-10(-4) M) produced a contraction increased by warming to 44 degreesC but not to 41 degreesC. The specific alpha2-adrenoceptor agonist BHT-920 produced a weak contraction, reduced by the alpha1-adrenoceptor antagonist prazosin (10(-6) M) and increased at 44 degreesC but not at 41 degreesC. The concentration-dependent contraction to endothelin-1 (ET-1; 10(-11)-10(-7) M) was increased by warming to 41 and 44 degreesC and by endothelium removal or L-NNA at 37 degreesC but not at 41 or 44 degreesC. Response to ET-1 was reduced by endothelin ETA-receptor antagonist BQ-123 (10(-5) M) and ETB-receptor antagonist BQ-788 (10(-5) M). In arteries precontracted with ET-1 (10(-8)-3 x 10(-8) M), relaxation to sodium nitroprusside (10(-8)-10(-4) M) was increased at 41 and 44 degreesC vs. at 37 degreesC, but that of ACh (10(-8)-10(-4) M) or adenosine (10(-8)-10(-4) M) was not different at all temperatures studied. Relaxation to ACh, but not adenosine, was reduced similarly by L-NNA at all temperatures studied. These results suggest hyperthermia in muscular arteries may inhibit production of, and increase dilatation to, NO, resulting in unchanged relaxation to ACh and increased constriction to KCl and ET-1, and may increase constriction to stimulation of alpha1-adrenoceptors by NO-independent mechanisms.

In vivo and in vitro action of endothelin-1 on goat cerebrovascular bed

This study concerned the effects and mechanisms of action of endothelin-1 on the cerebral circulation. Cerebral blood flow was electromagnetically measured in awake goats. Endothelin-1 (0.01-0.3 nmol) produced dose-dependent decreases in this flow (maximal reduction = 34%) and increases in cerebrovascular resistance (maximal increase = 74%) (P < 0.01). IRL 1620 (Suc-[Glu9, Ala11,15]endothelin-1-(8-21), agonist for endothelin ET(B) receptors, 0.01-0.3 nmol) slightly decreased cerebral blood flow. The effects of endothelin-1, but not those of IRL 1620, on cerebral blood flow were diminished by 50% during infusion of the antagonist for endothelin ET(A) receptors, BQ-123 (cyclo-(D-Asp-Pro-D-Val-Leu-Trp), 2 nmol min(-1)), but not affected during infusion of the antagonist for endothelin ET(B) receptors, BQ-788 (N-[N-[N-[(2,6-dimethyl-1-piperidinyl)carbonyl]-4-methyl-L-Leucyl-1-(met hoxycarbonyl)-D-tryptophyl]-Dnorleucine monosodium), 2 nmol min(-1)). Intravenous administration of NW-nitro-L-arginine methyl ester (L-NAME, 47 mg kg(-1)) or NW-nitro-L-arginine (L-NNA, 47 mg kg(-1)) reduced basal cerebral blood flow by 39 and 33%, increased cerebrovascular resistance by 108 and 98% and mean arterial pressure by 23 and 17%, and decreased heart rate by 27 and 25%, respectively (all at least P < 0.05). The increases in cerebrovascular resistance (as absolute values) induced by endothelin-1 were not affected during either L-NAME or L-NNA (as absolute values and percentages). Intravenous administration of meclofenamate (5 mg kg(-1)) did not change the cerebrovascular effects of endothelin-1 and IRL 1620. In isolated goat cerebral arteries under control, resting conditions, endothelin-1 (10(-11)-10(-7) M) induced concentration-dependent contractions (EC50 = 4.78 X 10(-9) M; maximal contraction = 3177+/-129 mg), whereas IRL 1620 (10(-11)-10(-7) M) produced no effect. This contraction produced by endothelin-1 was competitively blocked by BQ-123 (10(-7)-3 X 10(-6) M), and was not affected by BQ-788 (10(-6) and 10(-5) M). L-NAME (10(-4) M), meclofenamate (10(-5) M), indomethacin (10(-5) M), L-NAME (10(-4) M) plus meclofenamate (10(-5) M) and phosphoramidon (10(-4) M) did not affect the contraction in response to endothelin-1. Endothelium removal increased the response to endothelin-1, as well as the BQ-123 antagonism against endothelin-1 (pA2 values, 7.62 vs. 6.88; P < 0.01). In both intact and de-endothelized arteries precontracted with prostaglandin F2alpha endothelin-1 induced a further contraction, and IRL 1620 caused no effect. These results suggest that: (1) endothelin-1 produces cerebral vasoconstriction by activating endothelin ET(A) receptors probably located in smooth muscle; (2) endothelin ET(B) receptors, nitric oxide and prostanoids might be not involved in the cerebrovascular action of endothelin-1, and (3) endothelium removal may increase cerebrovascular reactivity by increasing sensitivity of endothelin ET(A) receptors to endothelin-1.

Coronary vasoconstriction produced by vasopressin in anesthetized goats. Role of vasopressin V1 and V2 receptors and nitric oxide

To examine the role of vasopressin V1 and V2 receptors, nitric oxide and prostanoids in the coronary vascular effects of [Arg8]vasopressin, coronary blood flow was measured with an electromagnetic flow transducer placed around the left circumflex (23 goats) or anterior descending (11 goats) coronary artery and vasopressin (0.03-1 microg) was intracoronarily injected in 34 anesthetized, open-chest goats. Basal mean values for coronary blood flow, mean systemic arterial pressure and heart rate, were 34 +/- 2.38 ml/min, 89 +/- 3.34 mmHg and 80 +/- 3.06 beats/min, respectively. Vasopressin produced dose-dependent decreases in coronary blood flow and the maximal reduction of this flow, attained with 1 microg of vasopressin, was 14 +/- 1.49 ml/min (42 +/- 2.64% of basal flow) (P < 0.01). Desmopressin (0.03-1 microg; 8 goats) did not affect significantly coronary blood flow. The intracoronary infusion of the antagonist for vasopressin V1 receptors d(CH2)5Tyr (Me) arginine vasopressin (2 microg/min per kg, 6 animals) significantly diminished the effects of vasopressin on coronary blood flow (the effects of 1 microg of vasopressin were reduced by 28%, P < 0.05). The mixed antagonist for vasopressin V1 and V2 receptors desGly-d(CH2)5-D-Tyr(Et)Val arginine vasopressin (0.2, 0.7 and 2 microg/min per kg, 9 animals) decreased in a dose-dependent manner the effects of vasopressin on coronary blood flow (the effects of 1 microg of vasopressin were decreased by 61% with 2 microg/min per kg, P < 0.01). Intracoronary infusion of saline (vehicle, 3 goats) did not change the effects of vasopressin on coronary blood flow. Intravenous administration of the inhibitor of nitric oxide synthesis N-omega-nitro-L-arginine methyl ester (L-NAME, 47 mg/kg, 9 animals) decreased resting coronary blood flow by 10% (P < 0.01) and augmented mean systemic arterial pressure by 20% (P < 0.01), without changing heart rate. During this treatment the reduction in coronary blood flow produced by vasopressin was higher than under control (the effects of 1 microg of vasopressin were increased by 28%, P < 0.01). Intravenous administration of the inhibitor of cyclooxygenase, meclofenamate (5 mg/kg, 7 animals), neither modified resting coronary blood flow, arterial pressure and heart rate nor the effects of vasopressin on this flow. These data indicate that vasopressin produces marked coronary vasoconstriction and suggest that: (a) it may be mediated by vasopressin V1 receptors, without involvement of vasopressin V2 receptors, (b) it is probably inhibited by nitric oxide under normal conditions and (c) it may be not modulated by prostanoids.

In vitro relaxation of dog cerebral veins in response to histamine is mediated by histamine H2 receptors

There is little information on the histamine receptor mechanisms involved in cerebral venodilation, thus the role of histamine present in human cerebrospinal fluid is difficult to assess. In isolated canine pial veins, concentration-response curves to histamine (10[-7]-10[-3] M), the histamine H1 receptor agonist, 2-pyridylethylamine (10[-6]-10[-2] M), the histamine H2 receptor agonist, dimaprit (S-(3-dimethylaminopropyl) isothiourea dihydrochloride, 10[-6]-10[-2] M), and the histamine H3 receptor agonist, imetit (S-[2-(1 midazol-4-yl)ethyl]isothiourea dihydrobromide, 10[-7]-10[-3] M) were isometrically determined. In resting veins, histamine, 2-pyridylethylamine and dimaprit had no significant effect, whereas in endothelin-1-precontracted veins, these drugs produced concentration-dependent relaxation (Emax in % of active tone and pD2 were: for histamine, 72 +/- 6 and 5.36 +/- 0.09; for 2-pyridylethylamine, 59 +/- 5 and 3.28 +/- 0.05; for dimaprit, 65 +/- 7 and 4.81 +/- 0.10, respectively). The relaxations in response to histamine and dimaprit were competitively antagonized by the histamine H2 receptor antagonist, cimetidine (3 x 10[-6]-10[-4] M) (pA2 = 6.07 +/- 0.03 for histamine, and 6.09 +/- 0.07 for dimaprit), but were not affected by the histamine H1 receptor antagonist, chlorpheniramine (10[-6] M) or the histamine H3 receptor antagonist, thioperamide (N-cyclohexyl-4-(1-H-imidazol-4-yl)-1-piperidine-carbothioamide maleate, 10[-6] M). The relaxation in response to 2-pyridylethylamine was inhibited by cimetidine (10[-5] M), but not by chlorpheniramine (10[-6] M). Imetit produced a small contraction in resting veins (14 +/- 4 mg) and precontracted veins (20 +/- 3 mg), which was not modified by thioperamide (10[-6] M). The relaxation of veins in response to histamine was not modified by endothelium removal, nor by the inhibitor of nitric oxide synthase, N(G)-nitro-L-arginine methyl ester (10[-4] M), or the cyclooxygenase inhibitor, meclofenamate (10[-5] M). Therefore, in pial veins: (1) histamine produces relaxation by activation of histamine H2 receptors, probably located in the smooth musculature, with no participation of histamine H1 and H3 receptors, and (2) endothelium, nitric oxide and prostanoids are probably not involved in the relaxation in response to histamine.

Role of the purinergic and noradrenergic components in the potentiation by endothelin-1 of the sympathetic contraction of the rabbit central ear artery during cooling

1. To examine the role of the purinergic and noradrenergic components in the potentiation of endothelin-1 on the vascular response to sympathetic nerve stimulation, we recorded the isometric response of isolated segments, 2 mm long, from the rabbit central ear artery to electrical field stimulation (1-8 Hz) under different conditions, at 37 degrees C during cooling (30 degrees C). 2. Electrical field stimulation produced frequency-dependent contraction, which was reduced during cooling (about 60% for 8 Hz). Both at 37 degrees C and 30 degrees C, phentolamine (1 microM) or blockade of alpha(1)-adrenoceptors with prazosin (1 microM) reduced, whereas blockade of alpha(2)-adrenoceptors with yohimbine (1 microM) increased, the contraction to electrical field stimulation. This contraction was increased after desensitization of P2-receptors with alpha, beta-methylene adenosine 5'-triphosphate (alpha, beta-meATP, 3 microM) at 37 degrees C but not at 30 degrees C, and was not modified by blockade of P2-receptors with pyridoxalphosphate-6-azophenyl-2,4'-disulphonic acid (PPADS, 30 microM) at either temperature. 3. Endothelin-1 (1, 3 and 10 nM) at 37 degrees C did not affect, but at 30 degrees C it potentiated in a concentration-dependent manner the contraction to electrical field stimulation (from 28 +/- 6 to 134 +/- 22%, for 8 Hz). At 37 degrees C, endothelin-1 in the presence of phentolamine or prazosin, but not in that of yohimbine, alpha, beta-meATP or PPADS, potentiated the contraction to electrical stimulation. At 30 degrees C, phentolamine or yohimbine reduced, prazosin did not modify and alpha, beta-meATP slightly increased the potentiation by endothelin-1 of the response to electrical stimulation. 4. The arterial contraction to ATP (2 mM) and the alpha(2)-adrenoceptor agonist BHT-920 (10 microM), but not that to (-)-noradrenaline (1 microM), was potentiated by endothelin-1 at both 37 degrees C and 30 degrees C. 5. These results in the rabbit central ear artery suggest that the sympathetic response: (a) at 37 degrees C, could be mediated mainly by activation of alpha(1)-adrenoceptors, with low participation of P2-receptors, (b) is diminished during cooling, probably by a reduction in the participation of alpha(1)-adrenoceptors, and in this condition the response could be mediated in part by P2-receptors, and (c) is potentiated by endothelin-1 during cooling, probably by increasing the response of both postjunctional alpha(2)-adrenoceptors and P2-receptors.

Role of endothelin receptors, calcium and nitric oxide in the potentiation by endothelin-1 of the sympathetic contraction of rabbit ear artery during cooling

1. To examine further the potentiation by endothelin-1 on the vascular response to sympathetic stimulation, we studied the isometric response of isolated segments, 2 mm long, from the rabbit central ear artery to electrical field stimulation (1-8 Hz), under different conditions, at 37 degrees C and during cooling (30 degrees C). 2. Electrical stimulation produced frequency-dependent contraction, which was reduced (about 63% for 8 Hz) during cooling. At 30 degrees C, but not at 37 degrees C, endothelin-1 (1, 3 and 10 nM) potentiated the contraction to electrical stimulation in a dose-dependent way (from 43 +/- 7% to 190 +/- 25% for 8 Hz). 3. This potentiation by endothelin-1 was reduced by the antagonist for endothelin ETA receptors BQ-123 (10 microM) but not by the antagonist for endothelin ETB receptors BQ-788 (10 microM). The agonist for endothelin ETB receptors IRL-1620 (0.1 microM) did not modify the contraction to electrical stimulation. 4. The blocker of L-type Ca2+ channels verapamil (10 microM l-1) reduced (about 72% for 8 Hz) and the unspecific blocker of Ca(2+)-channels NiCl2 (1 mM) practically abolished (about 98%), the potentiating effects of endothelin-1 found at 30 degrees C. 5. Inhibition of nitric oxide synthesis with NG-nitro-L-arginine (L-NOARG, 0.1 mM) increased the contraction to electrical stimulation at 30 degrees C more than at 37 degrees C (for 8 Hz, this increment was 297 +/- 118% at 30 degrees C, and 66 +/- 15% at 37 degrees C). Endothelium removal increased the contraction to electrical stimulation at 30 degrees C (about 91% for 8 Hz) but not at 37 degrees C. Both L-NOARG and endothelium removal abolished the potentiating effects of endothelin-1 on the response to electrical stimulation found at 30 degrees C. 6. These results in the rabbit ear artery suggest that during cooling, endothelin-1 potentiates the contraction to sympathetic stimulation, which could be mediated at least in part by increasing Ca2+ entry after activation of endothelin ETA receptors. This potentiating effect of endothelin-1 may require the presence of an inhibitory tone due to endothelial nitric oxide.

Role of nitric oxide in the effects of hypoglycemia on the cerebral circulation in awake goats

This study was performed to examine the role of nitric oxide in the effects of hypoglycemia on the cerebral circulation. Hypoglycemia was induced with insulin and its effects on cerebral blood flow (measured with an electromagnetic flow transducer placed on the internal maxillary artery) were studied in awake goats under control conditions and after administration of the nitric oxide synthesis inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 47 mg/kg). Also, cerebrovascular reactivity to vasodilator stimuli was examined during insulin-induced severe hypoglycemia, before and after L-NAME treatment. In five animals under control conditions (glycemia = 90 +/- 7 mg/dl, cerebral blood flow = 64 +/- 4 ml/min, mean systemic arterial pressure = 102 +/- 4 mmHg, cerebrovascular resistance = 1.62 +/- 0.11 mmHg/ml per min and heart rate = 73 +/- 6 beats/min), insulin decreased glycemia: when hypoglycemia was moderate (glycemia = 46 +/- 2 mg/dl) or severe (glycemia = 26 +/- 1 mg/dl) cerebral blood flow increased by 25 +/- 4% and 47 +/- 6%, and cerebrovascular resistance decreased by 18 +/- 3% and 34 +/- 4%, respectively. Under basal conditions, L-NAME did not affect glycemia but reduced resting cerebral blood flow by 37 +/- 2%, increased mean arterial pressure by 33 +/- 2% and decreased heart rate by 28 +/- 3%; after L-NAME, both moderate and severe hypoglycemia did not alter significantly resting cerebral blood flow and cerebrovascular resistance. In five other goats, L-NAME, administered during severe hypoglycemia, abolished the increase in cerebral blood flow, and increased cerebrovascular resistance and mean arterial pressure over the control (normoglycemic) values. In these animals with severe hypoglycemia, acetylcholine (0.01-1 microg), isoproterenol (0.03-3 microg) and diazoxide (0.3-9 mg), injected into the internal maxillary artery, decreased cerebrovascular resistance in a dose-dependent manner, and this decrease was similar before and after L-NAME. Therefore, insulin-induced hypoglycemia may produce cerebral vasodilatation by releasing nitric oxide and may diminish the capacity of the cerebral vasculature to release nitric oxide in response to acetylcholine.

Peptidergic modulation of the sympathetic contraction in the rabbit ear artery: effects of temperature

1. The effects of neuropeptide Y, endothelin-1, arginine-vasopressin and angiotensin II on the vascular contraction to sympathetic nerve stimulation were studied in isolated segments, 2 mm long, from the rabbit central ear artery, a cutaneous vessel, during changes in temperature (24 degrees -41 degrees C). 2. Transmural electrical stimulation (1-8 Hz, at supramaximal voltage) produced frequency-dependent contraction, and this response, partially blocked by tetrodotoxin (1 microM) and phentolamine (1 microM), was reduced by cooling (30 degrees C -24 degrees C) and was not modified by warming (41 degrees C), as compared to that recorded at 37 degrees C. 3. Pretreatment with neuropeptide Y (10, 30 and 100 nM) increased in a concentration-dependent manner the vascular contraction to sympathetic stimulation at every temperature studied, but this potentiation was greater during cooling (34 degrees C -24 degrees C) than at 37 degrees C or warming (41 degrees C). 4. Pretreatment with endothelin-1 (3 and 10 nM) or vasopressin (0.1, 0.3 and 1 nM) increased in a concentration-dependent manner the vascular contraction to sympathetic stimulation during cooling (34 degrees C -24 degrees C), but not at 37 degrees C or warming (41 degrees C). 5. Pretreatment with angiotensin II (0.1, 0.3 and 1 microM) did not modify the contraction to sympathetic stimulation at any temperature studied. 6. These results suggest that neuropeptide Y, endothelin-1 and vasopressin, but not angiotensin II, modulate the cutaneous vasoconstriction to sympathetic nerve stimulation by potentiating this vasoconstriction during cooling.

Noradrenaline content and release in male and female rat tail arteries

In tail-artery segments isolated from male and female control and gonadectomized rats, noradrenaline content and noradrenaline released by electrical stimulation were measured by high-pressure liquid chromatography. Noradrenaline content, expressed as a function of tissue wet weight, was higher in tail arteries from female than from male rats, but there were no significant differences between control and orchiectomized males or control and ovariectomized females. Electrical stimulation of vascular segments in the presence of cocaine (10(-5) M) and deoxycorticosterone (10(-5) M) induced release of noradrenaline that was increased in the presence of the alpha 2-adrenergic antagonist idaxozan (10(-6) M). However, no differences were found in either basal or stimulation-evoked fractional noradrenaline release between male or female, control or gonadectomized animals. These results indicate that control of noradrenaline release at the nerve ending does not appear to be different between genders. There may be differences in adrenergic density, but noradrenaline content does not appear to be modified by circulating gonadal hormones.

Coronary vasoconstriction by endothelin-1 in anesthetized goats: role of endothelin receptors, nitric oxide and prostanoids

The role of endothelin ETA and ETB receptors as well as of nitric oxide (NO) and prostanoids in the effects of endothelin-1 on the coronary circulation was studied in anesthetized goats. Where blood flow in the left circumflex coronary artery (coronary blood flow) (electromagnetically measured), systemic arterial pressure, left ventricle pressure and d P/dt, and heart rate were recorded. Endothelin-1 (0.01-0.3 nmol), intracoronarily injected, produced marked, dose-dependent reductions in basal coronary blood flow, ranging from 5% for 0.01 nmol to 75% for 0.3 nmol; 0.1 and 0.3 nmol endothelin-1 also reduced systolic ventricle pressure and dP/dt. The effects of endothelin-1 on coronary blood flow were diminished during intracoronary infusion of BQ-123 (cyclo-(D-Asp-Pro-D-Val-Leu-D-Trp). specific antagonist for endothelin ETA receptors. 2-16 nmol/min) in a dose-dependent way, but not during the infusion of BQ-788 (N-[N-[N-[(2.6-dimethyl-1-piperidinyl)carbonyl]-4-methyl-1-leucyl]-1- (methoxycarbonyl)-D-tryptophyl]-D-norleucine monosodium, specific antagonist for endothelin ETB receptors. 2-4 nmol/min). IRL 1620 (Suc-[Glu9, Ala11.15]endothelin-1-(8-21), specific agonist for endothelin ETB receptors. 0.01-0.3 nmol), intracoronarily injected. slightly reduced basal coronary blood flow only when 0.1 and 0.3 nmol were applied (maximal reduction about 25%); 0.3 nmol IRL 1620 also reduced systolic ventricle pressure and dP/dt. The effects of IRL 1620 were not modified by BQ-123 or BQ-788. NG-nitro-1-arginine methyl ester (L-NAME, inhibitor of NO synthesis, 47 mg/kg by i.v. route) reduced resting coronary blood flow by 10% and increased mean systemic arterial pressure and systolic ventricle pressure by 22 and 20%. respectively, without changing systolic ventricle dP/dt and heart rate. With L-NAME, the reductions of coronary blood flow by endothelin-1 were potentiated (P < 0.05), and those by IRL 1620 were not changed (P > 0.05). Meclofenamate (cyclooxygenase inhibitor, 4-6 mg/kg by i.v. route) modified neither the basal values of hemodynamic variables nor the coronary effects of endothelin-1 and IRL 1620. Therefore, endothelin-1 produces marked coronary vasoconstriction, which may be mediated by endothelin ETA receptors, with no participation of endothelin ETB receptors. NO, but not prostanoids, may produce a basal coronary vasodilator tone and may inhibit endothelin-1-induced coronary vasoconstriction. Also, it is suggested that the coronary vasoconstriction by endothelin-1 may impair cardiac performance due to heart ischemia.

Sex differences in the effects of 17 beta-estradiol on vascular adrenergic responses

The in vitro effects of 17 beta-estradiol on vascular responses to adrenergic nerve stimulation were studied in perfused tail arteries from age-matched male and female rats. Nerve stimulation resulted in vasoconstriction that was greater in male arteries. Addition of 17 beta-estradiol (3 x 10(-5) M) reduced the vasoconstrictor responses in both male and female arteries, but the reduction was significantly greater in the females. Gonadectomy of the animals for 1 month prior to the experiment did not alter the in vitro responses to 17 beta-estradiol in either males or females. 17 beta-Estradiol (10(-6) - 3 x 10(-5) M) also relaxed perfused tail arteries precontracted with KCl (50 mM); however the relaxation was not different between males and females, either intact or gonadectomized. Stimulation-evoked release of noradrenaline from adrenergic nerves of perfused tail arteries was measured, but no differences were found between males and females, nor was release modified by in vitro exposure to 17 beta-estradiol (10(-5) M). These results suggest that 17 beta-estradiol acts directly on postjunctional mechanisms to relax tail arteries of either sex. The effect of the hormone on arteries constricted by adrenergic nerve stimulation, however, is greater in females compared to males.

Regional differences in the arterial response to vasopressin: role of endothelial nitric oxide

1. The isometric response to arginine-vasopressin (10(-10)-10(-7)M) was studied in 2 mm long rabbit arterial segments isolated from several vascular beds (cutaneous, pial, renal, coronary, muscular, mesenteric and pulmonary). 2. Vasopressin induced contraction in central ear (cutaneous), basilar (pial), renal, coronary and saphenous (muscular) arteries, but had no effect in mesenteric and pulmonary arteries; the order of potency for the contraction was: ear > basilar > renal > coronary > saphenous arteries. 3. Treatment with the blocker of nitric oxide synthesis NG-nitro-L-arginine methyl ester (L-NAME; 10(-6)-10(-4) M) increased significantly (P < 0.05) the contraction to vasopressin in ear (148% of control), basilar (150% of control), renal (304% of control), coronary (437% of control) and saphenous (235% of control) arteries. Removal of the endothelium increased significantly (P < 0.05) the contraction to vasopressin in basilar (138% of control), renal (253% of control), coronary (637% of control) and saphenous (662% of control) arteries, but not in ear artery. Mesenteric and pulmonary arteries in the presence of L-NAME or after endothelium removal did not respond to vasopressin, as occurred in control conditions. 4. The specific antagonist for V1 vasopressin receptors d(CH2)5Tyr(Me)AVP (3 x 10(-9)-10(-7) M) was more potent (pA2 = 9.3-10.1) than the antagonist for both V1 and V2 vasopressin receptors desGly-d(CH2)5-D-Tyr(Et)ValAVP (10(-7)-10(-6) M) (pA2 = 7.4-8.4) to block the contraction to vasopressin of ear, basilar, renal and coronary arteries. 5. The specific V2 vasopressin agonist [deamino-Cys1, D-Arg8]-vasopressin (desmopressin) (10(-10)-10(-7) M) did not produce any effect in any effect in any of the arteries studied, with or without endothelium. 6. In arteries precontracted with endothelin-1, vasopressin or desmopressin did not produce relaxation. 7. These results suggest: (a) most arterial beds studied (5 of 7) exhibit contraction to vasopressin with different intensity; (b) the vasoconstriction to this peptide is mediated mainly by stimulation of V1 vasopressin receptors, and (c) endothelial nitric oxide may inhibit the vasoconstriction to this peptide, especially in coronary and renal vasculatures.

Role of nitric oxide and potassium channels in the cholinergic relaxation of rabbit ear and femoral arteries: effects of cooling

The main objective of this work was to study the role of potassium channels in the cholinergic relaxation of cutaneous arteries during cooling. Acetylcholine (10(-8)-10(-4) M) produced isometric concentration-dependent relaxation of precontracted segments of rabbit ear (cutaneous) and femoral (noncutaneous) arteries; this relaxation was higher at 24 degrees C (cooling) than at 37 degrees C in ear, but not in femoral, arteries. In both types of arteries, at 37 and 24 degrees C, the relaxation to acetylcholine was partially reduced by the inhibitor of nitric oxide synthase NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M), and the relaxation that remained after L-NAME was higher at 24 degrees C than at 37 degrees C in ear, but not in femoral, arteries. At 37 and 24 degrees C, the persistent relaxation to acetylcholine after L-NAME was further reduced by smooth muscle depolarization with medium containing a high concentration of potassium (6 x 10(-2) M), and with the nonspecific inhibitors of potassium channels tetraethylammonium (10(-2) M) or 4-aminopyridine (5 x 10(-3) M) in both ear and femoral arteries. In ear arteries, the inhibitor of high conductance calcium-activated potassium channels charybdotoxin (10(-7) M), alone or combined with L-NAME, reduced the relaxation to acetylcholine at 24 degrees C, but not at 37 degrees C. In femoral arteries, charybdotoxin alone did not modify, but combined with L-NAME reduced, the relaxation to acetylcholine at either temperature. At 37 and 24 degrees C, the inhibitor of low conductance calcium-activated potassium channels apamin (10(-7) M), the inhibitor of ATP-dependent potassium channels glibenclamide (10(-5) M) and the cyclooxygenase inhibitor meclofenamate (10(-5) M), alone or combined with L-NAME, did not modify the relaxation of both ear and femoral arteries to acetylcholine. These results suggest: (1) the cholinergic relaxation of cutaneous (ear) and noncutaneous (femoral) arteries could be mediated by endothelial nitric oxide and by activation of potassium channels, and (2) cooling increases the relaxation of cutaneous arteries to cholinergic stimulation, which may be mediated, in part, by an increased response of potassium channels.

Cooling effects on nitric oxide production by rabbit ear and femoral arteries during cholinergic stimulation

1. Ear (cutaneous) and femoral (deep) arteries from rabbit were perfused at 37 degrees C and 24 degrees C (cooling) and the production of nitrite, as an index of nitric oxide production, was measured under basal conditions and cholinergic stimulation. 2. In both types of arteries under control conditions, the basal production of nitrite was similar at 24 degrees C and 37 degrees C. Compared with the control conditions, the basal production of nitrite was significantly lower in ear and femoral arteries without endothelium or treated with NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) but it was similar in those treated with atropine (10(-6) M). 3. At 37 degrees C, methacholine (10(-7)-10(-5) M) increased the production of nitrite in ear and femoral arteries; this increase persisted during 30-60 min and was practically abolished by L-NAME (10(-4) M), atropine (10(-6) M), or removal of the endothelium. In ear arteries the total nitrite production to activation with methacholine was higher at 24 degrees C than at 37 degrees C due to this production persisted increased for a longer period (> 150 min), whereas in femoral arteries it was lower at 24 degrees C than at 37 degrees C. 4. It is suggested that: (a) the endothelium of rabbit ear and femoral arteries produce nitric oxide under basal conditions, which is increased by cholinergic stimulation, and (b) cooling potentiates endothelial nitric oxide production to cholinergic stimulation in cutaneous arteries, whereas it inhibits this production in deep arteries.

Cooling effects on the histaminergic response of rabbit ear and femoral arteries: role of the endothelium

The effects of cooling on the isometric response of rabbit isolated central ear (cutaneous) and femoral (non-cutaneous) arteries to histamine were determined at 37 degrees C and 24 degrees C (cooling). Under resting tension, both types of arteries contracted to histamine (10(-7)-10(-3) M), and the sensitivity of ear arteries, but not of femoral arteries was lower at 24 than at 37 degrees C. Chlorpheniramine (10(-7) M) blocked the contraction of both types of arteries to histamine at both temperatures. In ear arteries, endothelium removal or treatment with the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) did not affect the contraction to histamine at 37 degrees C, but it reversed the decreased contraction at 24 degrees C. In femoral arteries, endothelium removal or L-NAME (10(-5) M) did not affect the response to histamine at 37 and 24 degrees C. Ear and femoral arteries precontracted with endothelin-1 (10(-8)-10(-7) M) and pretreated with chlorpheniramine (10(-5) M) relaxed to histamine (10(-7)-10(-4) M), and the sensitivity of this relaxation in ear arteries, but not in femoral arteries, increased at 24 degrees C. The relaxation of ear and femoral arteries to histamine was not modified by endothelium removal, L-NAME (10(-5) M) or meclofenamate (10(-5) M), but it was blocked by cimetidine (10(-6) M) at 37 degrees C and 24 degrees C. These results suggest: (1) ear and femoral arteries have contracting H1 and relaxing H2 receptors, probably located on smooth musculature, and (2) cooling reduces the contraction and increases the relaxation of cutaneous arteries to histamine: the reduction of this contraction could be caused by an augmented availability of endothelial nitric oxide, and the increment of this relaxation could be caused by an augmented sensitivity of H2 receptors of smooth musculature induced by cooling. These features do not seem to occur in deep vessels.

Role of NO in goat basal cerebral circulation and after vasodilatation to hypercapnia or brief ischemias

The role of nitric oxide (NO) in the cerebral circulation under basal conditions and after vasodilatation to hypercapnia or reactive hyperemias was studied in 17 anesthetized goats. The intravenous administration of NG-nitro-L-arginine methyl ester (L-NAME, 3-4 or 8-10 mg/kg), an inhibitor of nitric oxide production, reduced middle cerebral artery (MCA) flow (electromagnetically measured) by 19 and 30% and increased systemic arterial pressure by 21 and 26%, respectively, whereas heart rate did not significantly change; MCA resistance increased by 48 and 86%, respectively. These hemodynamic effects were reversed by L-arginine (200-300 mg/kg iv; 5 goats). Different levels of hypercapnia (PCO2 of 30-35, 40-45, and 55-65 mmHg) (12 goats) produced arterial PCO2-dependent increases in MCA flow that were similar under control and L-NAME treatment. Graded cerebral hyperemia occurred after 5, 10, and 20 s of MCA occlusion in 5 goats, but its magnitude was decreased during L-NAME treatment. It suggests that, in the cerebral circulation, nitric oxide 1) produces a basal vasodilator tone and 2) is probably not involved in the vasodilatation to hypercapnia but may mediate hyperemic responses after short brain ischemias.

Reactivity of the dog cavernous carotid artery. The role of the arterial and venous endothelium

The cavernous carotid artery, that portion of the internal carotid artery that lies within the intracranial cavernous sinus, is covered by arterial (luminal surface) and venous (external surface) endothelium. The reactivity of the isolated canine, cavernous carotid artery, precontracted with 10(-5) M 5-hydroxytryptamine, was studied by using in vitro perfusion and superfusion to evaluate the effects of vasoactive stimuli applied to the internal or external surface. Acetylcholine (10(-8)-10(-4) M), thrombin (0.01-1 U/ml) or calcium ionophore A23187 (10(-8) - 10(-6) M) on the luminal side produced concentration-dependent relaxations which were reduced by the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) or by removing either the internal or both endothelia. Thrombin or ionophore A23187 on the external side produced concentration-dependent contractions which were reduced by removing either the external or both endothelia, and by meclofenamate (10(-5) M). Acetylcholine on the external side, produced a concentration-dependent contraction that was unaffected by meclofenamate or by removing the external or both endothelia. Sodium nitroprusside (10(-7) - 10(-5) M) induced similar relaxation on both sides and regardless of whether the arteries were with or without endothelium. These results suggest firstly, that the cavernous carotid artery responds to acetylcholine, thrombin or calcium ionophore A23187 by relaxing or contracting when these agents act on the luminal or the external surface respectively. Secondly, the arterial endothelium mediates relaxation to these three substances by releasing NO, whereas the venous endothelium mediates contraction to thrombin and ionophore A23187 by releasing a cyclooxygenase product.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral blood flow and cerebrovascular reactivity after inhibition of nitric oxide synthesis in conscious goats

1. The role of nitric oxide in the cerebral circulation under basal conditions and after vasodilator stimulation was studied in instrumented, conscious goats, by examining the action of inhibiting endogenous nitric oxide production with NG-nitro-L-arginine methyl ester (L-NAME). 2. In 6 unanaesthetized goats, blood flow to one brain hemisphere (electromagnetically measured), systemic arterial blood pressure and heart rate were continuously recorded. L-NAME (35 mg kg-1 by i.v. bolus) decreased resting cerebral blood flow by 43 +/- 3%, increased mean arterial pressure by 21 +/- 2%, and decreased heart rate by 41 +/- 2%; cerebrovascular resistance increased by 114 +/- 13% (P < 0.01); the immediate addition of i.v. infusion of L-NAME (0.15-0.20 mg kg-1 during 60-80 min) did not significantly modify these effects. Cerebral blood flow recovered at 72 h, arterial pressure and cerebrovascular resistance at 48 h, and heart rate at 6 days after L-NAME treatment. 3. A second treatment with L-NAME scheduled as above reproduced the immediate haemodynamic effects of the first treatment, which (except bradycardia) reversed with L-arginine (200-300 mg kg-1 by i.v. bolus). 4. Acetylcholine (0.01-0.3 micrograms), sodium nitroprusside (3-100 micrograms) and diazoxide (0.3-9 mg), injected into the cerebral circulation of 5 conscious goats, produced dose-dependent increases in cerebral blood flow, and decreases in cerebrovascular resistance; sodium nitroprusside (30 and 100 micrograms) also caused hypotension and tachycardia. 5. The reduction in cerebrovascular resistance from resting levels (in absolute values) to lower doses,but not to the highest dose, of acetylcholine was diminished, to sodium nitroprusside was increased, and to diazoxide was unaffected after L-NAME, compared to control conditions. The effects on cerebrovascular resistance to acetycholine normalized within 24 h and to sodium nitroprusside within 48 h after L-NAME treatment.6. This study provides information about the evolution of the changes in cerebral blood flow and cerebrovascular reactivity after inhibition of endogenous nitric oxide in conscious animals. The results suggest: (a) endogenous nitric oxide is involved in regulation of the cerebral circulation by producing a resting vasodilator tone, (b) the cerebral vasodilatation to acetylcholine is mediated, at least in part, by nitric oxide release, and (c) inhibition of nitric oxide production induces supersensitivity of cerebral vasculature to nitrovasodilators.

Role of the endothelium in the response to cholinoceptor stimulation of rabbit ear and femoral arteries during cooling

1. The role of the endothelium in the effects of cooling on the response to cholinoceptor stimulation of the rabbit central ear (cutaneous) and femoral (non-cutaneous) arteries was studied using 2 mm long cylindrical segments. 2. Concentration-response curves for acetylcholine (10(-9)-10(-5) M), methacholine (10(-9)-10(-5) M) and sodium nitroprusside (10(-9)-10(-4) M) were isometrically recorded in arteries under conditions, with and without endothelium or following pretreatment with the nitric oxide-synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 10(-6)-3 x 10(-4) M) at 37 degrees C and at 24 degrees C (cooling). 3. Ear and femoral arteries showed endothelium-dependent relaxation to acetylcholine and methacholine at 37 degrees C and 24 degrees C. The extent of relaxation of the control ear arteries, but not of the control femoral arteries, to acetylcholine and methacholine increased during cooling. 4. L-NAME (10(-6)-3 x 10(-4) M) reduced in a concentration-dependent way the response of ear arteries to acetylcholine at both 37 degrees C and 24 degrees C, this reduction being more potent at 37 degrees C. L-Arginine (10(-5)-10(-3) M) reversed in a concentration-dependent manner the inhibitor effects of 10(-5) M L-NAME at both temperatures. 5. Sodium nitroprusside caused a concentration-dependent relaxation in both arteries that was endothelium-independent. However, the extent of relaxation to this nitrovasodilator in ear and femoral arteries was lower at 24 degrees C. 6. These results suggest that cooling augments the reactivity of cutaneous (ear) arteries, but not that of non-cutaneous (femoral) arteries to cholinoceptor stimulation by endothelium-mediated mechanisms.Cooling could therefore facilitate the stimulated release of endothelial nitric oxide in cutaneous vessels.

Cerebrovascular and coronary effects of endothelin-1 in the goat

In vivo and in vitro effects of endothelin-1 (ET-1) on cerebral and coronary vasculature of goats were examined and compared. In six anesthetized goats intravenous injections of ET-1 (0.1-0.8 nmol) increased arterial pressure, did not change the middle cerebral (MCA) and left anterior descending or left circumflex coronary (LCC) arterial blood flows (electromagnetically measured), and increased cerebral and coronary vascular resistances. In four other anesthetized goats intra-arterial injections of ET-1 (0.01-0.3 nmol) decreased the MCA flow less than the LCC flow (maximal reduction was 20 and 80%, respectively) and only the highest dose increased arterial pressure. In isolated segments from large arteries ET-1 (10(-11) to 10(-7) M) caused concentration-dependent isometric contractions, the concentration causing 50% of the maximal effect and the maximal contraction being lower in cerebral arteries than in coronary arteries. The in vitro reactivity of both arteries was unaffected by endothelium removal or by indomethacin (10(-5) M). Therefore ET-1 produces cerebral and coronary vasoconstriction in vivo and in vitro, probably by acting directly on vascular musculature. Although the sensitivity is higher in isolated cerebral arteries than in coronary arteries, the reactivity in vivo could be lower in the cerebral circulation than in the coronary circulation to this endothelium-derived peptide.

Cooling and response to adrenoceptor agonists of rabbit ear and femoral artery: role of the endothelium

1. The effects of cooling on the response of the rabbit central ear (cutaneous) and femoral (non-cutaneous) arteries to stimulation of adrenoceptors and the role of the endothelium in these effects, were studied in 2 mm long cylindrical segments. 2. Concentration-response curves for noradrenaline (10(-9)-3 x 10(-4) M), phenylephrine (alpha 1-adrenoceptor agonist, 10(-9)-3 x 10(-4) M) and B-HT 920 (alpha 2-adrenoceptor agonist, 10(-7)-10(-3) M) were recorded isometrically in arteries with and without endothelium at 37 degrees C and at 24 degrees C (cooling). To analyze further the endothelial mechanisms in the responses to adrenoceptor stimulation during cooling, the effects of the adrenoceptor agonists on ear arteries in the presence of NG-nitro-L-arginine methyl esther (L-NAME) (10(-5) M) were also determined. 3. In every condition tested, the three adrenoceptor agonists produced a concentration-dependent arterial contraction and the order of potency in ear and femoral arteries was noradrenaline greater than or equal to phenylephrine greater than B-HT 920. The response of ear and femoral arteries to phenylephrine or B-HT 920 was blocked by prazosin (10(-6) M). Yohimbine (10(-6) M) decreased slightly the response of ear arteries and increased that of femoral arteries to B-HT 920. 4. The sensitivity of both ear and femoral arteries to the three adrenoceptor agonists was significantly lower at 24 degrees C than at 37 degrees C. 5. In ear arteries, endothelium removal or treatment with L-NAME did not influence the response at 37 degrees C, but did increase it during cooling to adrenoceptor stimulation.In femoral arteries, endothelium removal increased the sensitivity to noradrenaline and, especially, to B-HT 920 at 37 degrees C, but did not affect the response at 24 degrees C.6. The results suggest that: (a) rabbit ear and femoral arteries are equipped mainly with alpha 1-adrenoceptors;(b) at 37 degrees C, the contraction of the ear artery to adrenoceptor agonists is mostly endothelium-independent, and in the femoral artery the contraction to alpha 2-adrenoceptor activation is endothelium-dependent; (c) cooling inhibits the contraction to adrenoceptor agonists in both ear and femoral arteries: in the ear artery probably by increasing the availability of endothelial nitric oxide, but in the femoral artery by depressing the sensitivity of alpha-adrenoceptors in the smooth musculature.7. The results suggest that the endothelium may modulate the adrenoceptor response of cutaneous arteries during changes in temperature.

Effects of nitric oxide synthesis inhibition on the goat coronary circulation under basal conditions and after vasodilator stimulation

1. The role of nitric oxide in the coronary circulation under basal conditions and when exposed to various vasodilator stimuli was studied in instrumented, anaesthetized goats, by examining the action of inhibiting endogenous nitric oxide production with NG-nitro-L-arginine methyl ester (L-NAME). 2. In 12 goats, left circumflex coronary blood flow (electromagnetically measured), systemic arterial blood pressure and heart rate were continuously recorded. L-NAME (3-4, or 8-10 mg kg-1 injected i.v.) decreased resting coronary blood flow by 20 and 28%, increased mean arterial pressure by 23 and 30% and increased coronary vascular resistance by 47 and 65%, respectively, without affecting heart rate, or blood gases or pH. These haemodynamic effects were reversed by L-arginine (200-300 mg kg-1 by i.v. injection, 5 goats). 3. Acetylcholine (0.001-0.1 micrograms), sodium nitroprusside (0.01-0.3 mg), and diazoxide (0.1-3 mg), injected intracoronarily in 6 goats, produced dose-dependent increases in coronary blood flow; sodium nitroprusside (0.1-0.3 mg) also caused hypotension and tachycardia. 4. During the effects of L-NAME, the coronary vasodilatation to acetylcholine was attenuated, to sodium nitroprusside was increased, and to diazoxide was unaffected, in comparison with control conditions. The hypotensive effects of sodium nitroprusside were also increased during treatment with L-NAME. 5. Graded coronary hyperaemic responses occurred after 5, 10 or 20 s of coronary occlusion. The magnitude of hyerpaemia for each occlusion duration was increased during treatment with L-NAME, in comparison to control.6. The results suggest: (a) endogenous nitric oxide is involved in regulation of coronary circulation by producing a basal vasodilator tone, (b) acetylcholine-induced coronary vasodilatation is mediated, in part, by nitric oxide, and (c) inhibition of basal endogenous nitric oxide production induces supersensitivity of coronary vessels to nitrovasodilators and enhances hyperaemic responses after short periods of ischaemia of the myocardium.

Carotid blood flow in anesthetized rats: effects of carotid ligation and anastomosis

An experimental model was developed for continuous measurement of the common carotid blood flow, in the anesthetized rat, with an electromagnetic flowmeter. The mean carotid blood flow for 41 rats averaged 3.2 +/- 0.2 ml/min at an average mean arterial pressure of 101 +/- 2.5 mm Hg and arterial pO2 of 106 +/- 3.4 mm Hg, pCO2 of 38 +/- 1.2 mm Hg, and pH of 7.36 +/- 0.02. This model allowed short- and long-term carotid hemodynamic changes to be recorded after contralateral carotid ligation or end-to-side carotid anastomosis. After ligation of the contralateral carotid, blood flow through the intact carotid increased 25% (at about 1 week) and 45% (at about 5-6 months), whereas, after anastomosis, carotid blood flow increased 76% and 89% at periods comparable to those after ligation. Arterial pressure and gases did not change throughout the experimental periods. Probable mechanisms involved in these carotid hemodynamic changes are discussed.

Response of rabbit ear artery to endothelin-1 during cooling

1. The effects of cooling on the response of rabbit central ear artery to endothelin-1 and the role of the endothelium in these effects were studied in 2 mm long cylindrical arterial segments. 2. Concentration-response curves for endothelin-1 (10(-10)-3 x 10(-7) M) were recorded isometrically in arteries with and without endothelium at 37 degrees C and during cooling (24 degrees C). To analyze further the endothelial mechanisms of the response to endothelin-1 during cooling, the effects of this peptide in the presence of NG-nitro-L-arginine methyl ester (L-NAME) (10(-4) M) or meclofenamate (10(-5) M) were also determined. 3. In every condition tested, endothelin-1 produced a marked, concentration-dependent arterial contraction. Sensitivity of intact arteries to this peptide was consistently lower at 24 degrees C than at 37 degrees C. At 37 degrees C there were comparable responses of arteries with and without endothelium, but at 24 degrees C arteries without endothelium showed a higher sensitivity than intact arteries to endothelin-1. 4. L-NAME (10(-4) M) increased the maximal contraction at 37 degrees C, and both the sensitivity and maximal contraction at 24 degrees C of intact arteries to endothelin-1. Meclofenamate (10(-5) M) did not affect the arterial response to endothelin-1. 5. Sensitivity of arteries with and without endothelium to nitroprusside (10(-9)-10(-3) M) was significantly decreased during cooling, and endothelium removal did not affect the relaxation to this nitrovasodilator. 6. These results suggest that cooling decreases sensitivity of cutaneous arteries (ear artery) to endothelin-1 probably by increasing the availability of endothelial nitric oxide.

Response of canine internal carotid system to acetylcholine

The reactivity of the canine internal carotid system to acetylcholine (10(-8)-10(-4) M) was studied isometrically with 4-mm cylindrical segments from cervical and cavernous portions of the internal carotid artery and from the middle cerebral artery. Under control conditions, the cervical portion relaxed to every dose, the cavernous portion relaxed at low concentrations (10(-8)-10(-6) M) and contracted at higher concentrations (10(-5)-10(-4) M), whereas the middle cerebral artery contracted to every dose of acetylcholine. These responses were blocked by atropine (10(-6) M). Without endothelium, the cervical portion exhibited a lower relaxation, the cavernous portion contracted, and the middle cerebral artery was practically unresponsive to acetylcholine. These responses were also blocked by atropine. It suggests that the reactivity of the internal carotid system to acetylcholine 1) is endothelium dependent and 2) changes as it courses toward the brain, and this could be related to different embryological origin of the components of this arterial system.

Endothelin action on cerebral circulation in unanesthetized goats

The effects of endothelin 1 on the internal maxillary artery blood flow, measured as an index of cerebral blood flow, were examined in six unanesthetized goats under control conditions, hypercapnia induced by inhalation of 10% CO2 in air, hypertension by intravenous infusion of norepinephrine, and hypotension by intravenous injection of diazoxide. Under control, administration of endothelin (0.01-0.3 nmol) into the internal maxillary artery produced dose-dependent sustained decreases in cerebral blood flow and increases in cerebrovascular resistance; higher doses (0.1 and 0.3 nmol) also caused hypertension and bradycardia. During hypercapnia or hypertension, endothelin did not significantly affect cerebral blood flow, and only higher doses (0.1 and/or 0.3 nmol) increased cerebrovascular resistance, but this was lower than under control. However, under hypotension endothelin evoked a higher reduction in cerebral blood flow and increment in cerebrovascular resistance, and systemic effects were also more marked than under control. Therefore endothelin is a potent cerebral vasoconstrictor, and this effect is very attenuated during hypercapnia and hypertension but is increased under hypotension.

Alpha 1- and alpha 2-adrenergic response in human isolated skin arteries during cooling

1. Dose-response curves for noradrenaline, phenylephrine and clonidine were determined isometrically in 2-mm cylindrical segments from human skin arteries at 24 degrees C and compared to those previously reported at 37 degrees C. 2. Noradrenaline (3 x 10(-10)-3 x 10(-4) M) induced dose-dependent contraction and the sensitivity was increased during cooling. Phentolamine (10(-6) M), prazosin (10(-6) M) or yohimbine (10(-6) M) produced a higher rightward shift of the control curve for noradrenaline during cooling. 3. Phenylephrine (10(-11)-3 x 10(-4) M) and clonidine (10(-11)-10(-6) M) caused dose-dependent contraction and the sensitivity of the arteries was augmented at 24 degrees C. 4. The arteries also showed a lower maximal contraction to the adrenergic agonists used and KCl (50 mM) during cooling. 5. The results suggest that cooling: (a) increases sensitivity of postjunctional alpha 1- and alpha 2-adrenoceptors in human skin arteries and (b) depresses contractility of these arteries to alpha-adrenergic stimulation and direct activation of vascular smooth muscle.

In vitro reactivity of dog cavernous carotid artery to stretch and adrenergic stimulation

The reactivity of the dog cavernous carotid artery to stretch, field electrical stimulation, and norepinephrine was studied using arterial segments under isometric conditions. Light microscopy revealed that this artery is of muscular type and its external surface is covered by venous endothelium, and fluorescence microscopy showed a dense adrenergic innervation. On stretch, arteries exhibited an immediate, transient contraction (phasic response) and a late, maintained contraction (tonic response) that were unaffected by tetrodotoxin (10(-6) M) or endothelium removal but were reduced by the inhibitors of cyclooxygenase indomethacin (10(-6) M), acetylsalicylic acid (3 x 10(-5) M), or meclofenamate (10(-5) M). Electrical stimulation (0.5-4 Hz) contracted the arteries in a frequency-dependent manner, and the response was reduced by tetrodotoxin, phentolamine, (10(-6) M), or the inhibitors of cyclooxygenase used but was unaffected by endothelium removal. Norepinephrine (10(-9)-3 x 10(-4) M) caused dose-dependent contraction that was blocked by phentolamine and by the inhibitors of cyclooxygenase but was not modified by endothelium removal. The results indicate that the dog cavernous carotid artery develops myogenic tone on stretch and contracts on adrenergic stimulation. They also suggest that in these responses prostaglandins but not the endothelium are involved. Therefore, the cavernous carotid artery, because of its location and reactivity, could be of relevance in regulating blood flow or pressure within the cerebral circulation when arterial pressure or adrenergic activity increases.

Effect of dietary sodium intake on the pressor reactivity to angiotensin II in rats with experimental cirrhosis of the liver

The present experiments were designed to evaluate vascular reactivity to angiotensin II in rats with experimental cirrhosis of the liver (induced with CCl4 and phenobarbital) before ascites appearance. The systemic pressor response to angiotensin II in conscious animals and the contractile effect of angiotensin II in isolated femoral arteries were studied. In addition, the effect of high sodium intake on these parameters was also analyzed. Both renin and aldosterone plasma concentrations were similar in control and cirrhotic rats on the normal or on the high sodium diet. Basal mean arterial pressure was higher in control rats than in cirrhotic rats on the normal sodium (116 +/- 4 vs. 101 +/- 4 mmHg (1 mmHg = 133.3 Pa), p less than 0.05) or on the high sodium diet (118 +/- 7 vs. 98 +/- 6 mmHg). No differences in plasma renin activity or plasma aldosterone were found between control and cirrhotic rats. Upon injection of angiotensin II, control rats show a dose-dependent increase in mean arterial pressure which is higher in high sodium than in normal sodium rats. Cirrhotic rats showed a lower hypertensive response to angiotensin II than their corresponding control rats. In addition, no difference between pressor responses to angiotensin II was observed when normal sodium and high sodium cirrhotic rats were compared. On application of angiotensin II, femoral arteries of control and cirrhotic rats exhibited a dose-dependent contraction. However, maximal contraction was higher in high sodium control rats (145 +/- 12 mg) than in normal sodium control rats (99 +/- 6 mg, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Postjunctional alpha-1 and alpha-2 adrenoceptors in human skin arteries. An in vitro study

Experiments were performed to characterize the postjunctional alpha adrenoceptors that mediate adrenergic constriction in human skin arteries. Abdominal s.c. arteries were obtained from patients who died 3 to 12 hr before, and vascular segments 2 mm in length and 600 to 1050 microns in external diameter were prepared for isometric tension recording. On application of norepinephrine, phenylephrine (alpha-1 adrenergic agonist) or clonidine (alpha-2 adrenergic agonist) the arteries contracted in a dose-dependent manner and, in terms of the mean EC50 values, the order of potencies was clonidine greater than norepinephrine greater than phenylephrine. With regard to their ability to induce maximal contraction, the order was norepinephrine = phenylephrine greater than clonidine. In the presence of phentolamine (nonspecific alpha adrenergic antagonist) or yohimbine (selective alpha-2 adrenergic antagonist) the control curve for norepinephrine was displaced to the right in a parallel way. Prazosin (selective alpha-1 adrenergic antagonist) depressed both the slope and maximal response of the control curve for norepinephrine but the shift was not significant. Prazosin and yohimbine produced a parallel rightward shift in the control curve for phenylephrine and clonidine, respectively. These results suggest that skin arteries of humans have a mixed population of postjunctional alpha-1 and alpha-2 adrenoceptors and that alpha-2 adrenoceptors are more prominent. They also suggest that the alpha-2 adrenergic component of the response to norepinephrine is a low-maximum effect compared to the alpha-1 adrenergic component. This could be of significance in regulating skin blood flow and thermoregulatory function.

Mechanics of arteries forming the carotid rete of goat and cattle

To determine the mechanics of arteries forming the carotid rete mirabile of goat and cattle, the wall tension-circumference length relationship was recorded isometrically in isolated retial arteries of 350-600 microns in external diameter under relaxed and potassium-activated conditions. The results are compared to those of pial arteries of similar size. In relaxed retial and cerebral vessels, tension-length relationship had nonlinear characteristics and the incremental elastic modulus rose as the circumference length increased, the modulus being lower in retial than in pial arteries. However, the stiffness of the artery considered as a whole (stiffness parameter beta) was similar in the two types of vessels. In activated arteries, force development was a function of length and the magnitude of the response increased until an optimal length was reached after which the response decreased with further stretch. In all stretches studied the developed force was much lower in retial arteries. The calculated active stress at the various lengths was also smaller in retial than in cerebral arteries and the maximum active stress for retial arteries was about 30-50% of that for cerebral arteries. Therefore, the passive mechanical properties of retial arteries closely resemble those of cerebral arteries but retial arteries have a small contractility. This suggests that the carotid rete mirabile of Artiodactyla has a minor role in actively controlling blood supply to the brain. Comments on the hemodynamic significance of the carotid rete are included.

Hemodynamic significance of the carotid rete during changes in arterial blood pressure

We attempted to characterize in the goat the hemodynamic response of the carotid rete during large, passive changes in blood pressure in the afferent limb of the rete produced by mechanical constriction of the thoracic aorta or the inferior vena cava. Experiments in 12 anesthetized goats demonstrated that calculated resistance through the rete decreases in hypertension and increases in hypotension, whereas changes in resistance through brain vessels follow opposite directions. The consequence of this is that the carotid rete, by passively decreasing its resistance to blood flow in hypertension, acts as a flow-facilitating system in a situation in which smooth muscle of brain vessels contracts in response to stretch. Contrariwise, by increasing its resistance to blood flow during systemic hypotension, the carotid rete "limits" the passage of blood when active relaxation of brain vessels takes place.