Calcium, phosphoinositide, and 1,2-diacylglycerol responses of blood vessels of deoxycorticosterone acetate-salt hypertensive rats to endothelin-1

Hyperparathyroidism and the Calcium Paradox of Aldosteronism

BACKGROUND

Aldosteronism may account for oxi/nitrosative stress, a proinflammatory phenotype, and wasting in congestive heart failure. We hypothesized that aldosterone/1% NaCl treatment (ALDOST) in rats enhances Ca2+ and Mg2+ excretion and leads to systemic effects, including bone loss.

METHODS AND RESULTS

At 1, 2, 4, and 6 weeks of ALDOST, we monitored Ca2+ and Mg2+ excretion, ionized [Ca2+]o and [Mg2+]o, parathyroid hormone and 1-antiproteinase activity in plasma, bone mineral density, bone strength, Ca2+ and Mg2+ content in peripheral blood mononuclear cells (PBMCs) and ventricular tissue, and lymphocyte H2O2 production. A separate group received spironolactone (Spiro), an aldosterone receptor antagonist. Age- and gender-matched unoperated and untreated rats served as controls. ALDOST induced a marked (P<0.05) and persistent rise in urinary and fecal Ca2+ and Mg2+ excretion, a progressive reduction (P<0.05) in [Ca2+]o and [Mg2+]o, and an elevation in parathyroid hormone (P<0.05) with a fall (P<0.05) in bone mineral density and strength. An early, sustained increase (P<0.05) in PBMC Ca2+ and Mg2+ was found, together with an increase (P<0.05) in tissue Ca2+. Plasma 1-antiproteinase activity was reduced (P<0.05), whereas lymphocyte H2O2 production was increased (P<0.05) at all time points. Spiro cotreatment attenuated (P<0.05) urinary and fecal Ca2+ and Mg2+ excretion, prevented the fall in [Ca2+]o and [Mg2+]o, rescued bone mineral density and strength, and prevented Ca2+ overloading of PBMCs and cardiomyocytes.

CONCLUSIONS

In aldosteronism, Ca2+ and Mg2+ losses lead to a fall in [Ca2+]o and [Mg2+]o with secondary hyperparathyroidism and bone resorption. Ca2+ overloading of PBMCs and cardiac tissue leads to oxi/nitrosative stress and a proinflammatory phenotype.

Contribution of endogenous endothelin in the enhanced coronary constriction in DOCA-salt hypertensive rats

OBJECTIVE

The present study was performed to evaluate the hypersensitivity to vasoconstrictors in coronaries from uninephrectomized hypertensive rats (HTR), after a 2-week deoxycorticosterone acetate (DOCA)-salt treatment, in comparison with uninephrectomized age-matched normotensive rats (NTR).

DESIGN AND METHODS

Coronary resistance was recorded from isolated Langendorff hearts perfused at a constant flow rate.

RESULTS

Cumulative dose-response curves to vasopressin, angiotensin II and endothelin in HTR showed an enhanced maximal response, in comparison with NTR (P< 0.05). In contrast, the sensitivity to U-46619, a thromboxane-mimetic agonist, was reduced in HTR in comparison with NTR (P< 0.05). In the presence of ET(A)/ET(B)-receptor antagonists, LU-302 872 (10 micromol/l) and PD-142 893 (0.1-1 micromol/l), cumulative dose-response curves to vasopressin and angiotensin II showed a reduced maximal response in HTR compared with NTR (P< 0.05). LU-302 872 did not change the responsiveness to U-46619 in both groups. Perfusion of hearts from NTR with a subpressor concentration of endothelin-1 (10 pmol/l) potentiated the responsiveness to vasopressin and angiotensin II, but not that of U-46619 (P< 0.05). Hypertension did not alter the dose-response curves obtained with phorbol 12-myristate 13-acetate, an activator of protein kinase C, Bay K 8644, a L-type calcium-channel activator, and KCl. Measurement of endothelin release by radioimmunoassay in the coronary effluent, before and during dose-response curves to vasopressin, angiotensin II and U-46619, showed no significant increase by the vasoconstrictors, although basal endogenous endothelin was increased in HTR (P< 0.05).

CONCLUSION

Two-week DOCA-salt hypertension is associated with enhanced coronary vasoconstrictor effects of endothelin, vasopressin and angiotensin II. An increased basal release of endogenous endothelin in coronaries from HTR, along with an enhanced responsiveness of the coronary smooth muscle to endothelin, may contribute to the potentiated response to vasoconstrictors. L-type calcium-channels and protein kinase C are not involved in this increased coronary reactivity to vasoconstrictors in HTR.

Decreased endothelin binding and [Ca2+]i signaling in microvessels of DOCA-salt hypertensive rats

OBJECTIVES AND DESIGN

The deoxycorticosterone acetate (DOCA)-salt model of hypertension is characterized by elevated vascular endothelin-1 (ET-1) and by reduced contraction to ET-1 in isolated mesenteric small arteries. The decreased contraction to ET-1 may be a compensatory mechanism caused by elevations in ET-1 and arterial pressure. The present study was designed to determine whether down-regulation of endothelin receptors or altered Ca2+ signaling contribute to the decreased contraction to ET-1.

METHODS AND RESULTS

Contraction to ET-1 (10 to 10 mol/l) was significantly reduced in isolated mesenteric small arteries (87-286 microm intraluminal diameter) from DOCA-salt rats compared with placebo rats. Membrane protein was obtained for measurement of [125I]ET-1 receptor binding and ET receptor expression. Maximum binding was significantly reduced in vascular membranes from DOCA-salt rats (670 +/- 71 fmol/mg protein) compared with placebo rats (1165 +/- 75 fmol/mg protein), but binding affinity was unchanged. Conversely, ETA receptor protein was increased in DOCA-salt rat vessels. To assess Ca2+ signaling, freshly dissociated mesenteric small artery smooth muscle cells were loaded with fura-2 for measurement of the average myoplasmic free Ca2+ concentration ([Ca2+ ] ). The ET-1 (10 mol/l) induced increase in [Ca2+ ] was significantly less in cells from DOCA-salt rats compared with from placebo rats. This effect was not due to a loss of L-type Ca2+ channels since expression was increased in membrane protein from DOCA-salt rats compared with placebo rats, as measured by Western blot analysis.

CONCLUSIONS

These findings indicate that decreases in receptor binding and Ca2+ signaling contribute to the impaired contraction to ET-1 in DOCA-salt hypertensive rats. However, these changes are not due to reduced expression of ETA receptors or L-type Ca2+ channels.

Gender differences in vascular expression of endothelin and ET(A)/ET(B) receptors, but not in calcium handling mechanisms, in deoxycorticosterone acetate-salt hypertension

We determined if the increased vascular responsiveness to endothelin-1 (ET-1) observed in male, but not in female, DOCA-salt rats is associated with differential vascular mRNA expression of ET-1 and/or ET A/ET B receptors or with functional differences in Ca2+ handling mechanisms by vascular myocytes. Uninephrectomized male and female Wistar rats received DOCA and drinking water containing NaCl/KCl. Control rats received vehicle and tap water. Blood pressure and contractile responses of endothelium-denuded aortic rings to agents which induce Ca2+ influx and/or its release from internal stores were measured using standard procedures. Expression of mRNA for ET-1 and ET A/ET B receptors was evaluated by RT-PCR after isolation of total cell RNA from both aorta and mesenteric arteries. Systolic blood pressure was higher in male than in female DOCA rats. Contractions induced by Bay K8644 (which activates Ca2+ influx through voltage-operated L-type channels), and by caffeine, serotonin or ET-1 in Ca2+-free buffer (which reflect Ca2+ release from internal stores) were significantly increased in aortas from male and female DOCA-salt compared to control aortas. DOCA-salt treatment of male, but not female, rats statistically increased vascular mRNA expression of ET-1 and ET B receptors, but decreased the expression of ET A receptors. Molecular up-regulation of vascular ET B receptors, rather than differential changes in smooth muscle Ca2+ handling mechanisms, seems to account for the increased vascular reactivity to ET-1/ET B receptor agonists and higher blood pressure levels observed in male DOCA-salt rats.

Role of ET-1 receptor binding and [Ca(2+)](i) in contraction of coronary arteries from DOCA-salt hypertensive rats

Hypertension is associated with an increase in coronary artery disease, but little is known about the regulation of coronary vascular tone by endothelin-1 (ET-1) in hypertension. The present study evaluated the mechanisms mediating altered contraction to ET-1 in coronary small arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. DOCA-salt rats exhibited an increase in systolic blood pressure and plasma ET-1 levels compared with placebo rats. Contraction to ET-1 (1 x 10(-11) to 3 x 10(-8) M), measured in isolated coronary small arteries maintained at a constant intraluminal pressure of 40 mmHg, was largely reduced in vessels from DOCA-salt rats compared with placebo rats. To determine the role of endothelin receptor binding in the impaired contraction to ET-1, (125)I-labeled ET-1 receptor binding was measured in membranes isolated from coronary small arteries. Maximum binding (fmol/mg protein) and binding affinity were similar in coronary membranes from DOCA-salt rats compared with placebo rats. Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured in freshly dissociated coronary small artery smooth muscle cells loaded with fura 2. ET-1 (10(-9) M) produced a 30 +/- 9% increase in [Ca(2+)](i) in smooth muscle cells from placebo rats, but had no effect on cells from DOCA-salt rats (2 +/- 2%). In summary, the ET-1-induced coronary artery contraction and increase in [Ca(2+)](i) are impaired in DOCA-salt hypertensive rats, whereas endothelin receptor binding is not altered. These results suggest endothelin receptor uncoupling from signaling mechanisms and indicate that impaired [Ca(2+)](i) signaling contributes to the decrease in ET-1-induced contraction of coronary small arteries in DOCA-salt hypertensive rats.

Altered cardiac endothelin receptors and protein kinase C in deoxycorticosterone-salt hypertensive rats

The aim of the present study was to assess the status of ET-1 receptor subtypes (ET(A)and ET(B)) in ventricular myocytes and fibroblasts and to determine the role of PKC-dependent pathways in ET-1-stimulated cardiac cells in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Systolic blood pressure and relative heart to body weight were significantly increased in DOCA-salt rats. In unilaterally nephrectomized (Uni-Nx) control rats, more than 90% of cardiomyocyte ET receptors were of the ET(A)subtype, whereas in fibroblasts ET(A)and ET(B)receptors were present in a 1:3 ratio. In DOCA-salt rats, the density of the ET(A)receptor subtype was reduced by 31% in cardiomyocytes and in cardiac fibroblasts only ET(B)receptor density was decreased by 29%. Affinity was unchanged. The relative expression of immunoreactive PKC alpha, gamma and epsilon was significantly increased, whereas PKC delta was not altered in cardiac extracts of DOCA-salt rats. In cardiac fibroblasts from DOCA-salt rats PKC delta was significantly increased and PKC epsilon was not translocated after ET-1 stimulation. The hearts of DOCA-salt hypertensive rats are thus characterized by: (1) decreased density of cardiomyocyte ET(A)receptors and fibroblast ET(B)receptors; (2) cell-specific enhanced expression of some PKC isoenzymes (alpha, gamma, delta and epsilon); and (3) unresponsiveness of PKC epsilon to translocate in the presence of ET-1. Together with alterations of ET-1-induced Ca(2+)handling in cardiac myocytes and fibroblasts, which we previously reported, results from the present study indicate a marked modification of the cardiac ET-1 system of DOCA-salt hypertensive rats.

The effects of short-term nifedipine treatment on responsiveness of aortic rings of cadmium-hypertensive rats

The effects of short-term antihypertensive treatment with nifedipine on blood pressure and vascular responsiveness were studied in cadmium-hypertensive and normotensive control rats. Cadmium administration caused a significant increase in mean arterial blood pressure. Endothelin-1, noradrenaline and angiotensin II produced concentration dependent contractions of aortic rings that attained a lower maximal contraction in cadmium-hypertensive rats. Responses of aortic rings to KCl did not show a significant difference between the groups. Nifedipine administered simultaneously with cadmium inhibited the induction of hypertension. Nifedipine treatment for 5 days significantly reduced the blood pressure in cadmium-hypertensive and normotensive rats. Neither inhibition of hypertension nor normalization of blood pressure in cadmium-hypertensive rats caused an alteration in contractile responses of aortic rings to vasoconstrictors which suggested that development of decreased vascular reactivity and of hypertension occurs simultaneously in cadmium-hypertensive rats but the role of decreased vascular reactivity in maintenance of hypertension is questionable in cadmium-hypertension.

Endothelin, vascular hypertrophy, and hypertension

The endothelins (ET-1, 2, and 3) constitute a family of 21 amino-acid peptides with potent biological activities. They are synthesized in several tissues, including the vascular endothelium (ET-1 exclusively) and smooth muscle cells. The production and release of endothelin is stimulated by many factors, hormonal and metabolic, and by growth factors, hypoxia, and shear stress. Released endothelin binds to the endothelin receptors ETA and ETB, the ETA receptors on vascular smooth muscle cells mediating vasoconstriction, and the ETB receptors on the endothelium linked to nitric oxide (NO) and prostacyclin release. The ETA receptors activate the PLC-IP3-DAG transduction pathway, which through an increase in cytosolic Ca2+ and protein kinase C (PKC) causes vasoconstriction and stimulation of vascular smooth muscle cell growth and proliferation. In the pathogenesis of vascular hypertrophy in hypertension, there is a complex interaction between endothelin, angiotensin II, alpha-adrenergic agonists, Ca2+, and other growth factors. In animal models of hypertension, endothelin causes vascular hypertrophy, more pronounced in deoxycorticosterone acetate (DOCA)-salt hypertension in the rat than in the spontaneously hypertensive rate. In humans there is an increase in the plasma concentration of endothelin in severe atherosclerotic disease, but not consistently in hypertension. Evidence for the role of endothelin in the vascular hypertrophy of human hypertension is scanty, but the development of nonpeptide and receptor subtype-selective antagonists will permit meaningful studies, including clinical trials of a new class of antihypertensive agents.

Endothelin-1-induced contraction in isolated aortae from normotensive and DOCA-salt hypertensive rats: effect of magnesium

1. The contractile responses to endothelin-1 and the effect on these of various magnesium concentrations, were studied in isolated aortic rings from normotensive Sprague-Dawley rats and deoxycorticosterone acetate-salt (DOCA-salt) hypertensive rats. 2. Contractions induced by endothelin-1 were smaller in endothelium-denuded aortae from DOCA-salt hypertensive rats than in those from normotensive rats. The absence of calcium in the medium attenuated endothelin-1-induced contractions of aortae from both normotensive and DOCA-salt rats, but the contraction was greater in aortae from DOCA-salt hypertensive rats. Ryanodine (which inhibits the release of intracellular calcium) inhibited endothelin-1-induced contractions in aortae from DOCA-salt hypertensive rats to a greater extent than in aortae from normotensive rats. 3. A high extracellular magnesium concentration (4.8 mM) attenuated endothelin-1-induced contractions in tissues from DOCA-salt hypertensive rats but not in tissues from normotensive rats. In the absence of calcium, a high concentration of magnesium attenuated endothelin-1-induced contraction in aortae from both normotensive and hypertensive rats. In the presence of ryanodine, a high concentration of magnesium did not modify the contraction in preparations from either strain. 4. Absence of magnesium attenuated endothelin-1-induced contractions in aortae from both normotensive and DOCA-salt hypertensive rats. In the absence of calcium, removal of magnesium totally inhibited endothelin-1-induced contraction in tissues from normotensive rats but had no effect in those from hypertensive rats. In the presence of ryanodine, the lack of magnesium inhibited endothelin-1-induced contractions in aortae from DOCA-salt hypertensive rats but increased the sensitivity to endothelin-1 of aortae from normotensive rats. 5. The presence of endothelium did not modify the effect of high magnesium on endothelin-1-induced contractions in aortae from normotensive and DOCA-salt hypertensive rats. Conversely, the attenuating effect of magnesium removal on endothelin-1-induced contractions did not occur when endothelium was present. 6. In conclusion, endothelin-1-induced contraction was blunted in aortae from DOCA-salt hypertensive rats. The blunted response was related to altered calcium utilization during contraction. Changes in extracellular magnesium concentration differentially alter endothelin-1-induced contraction in aortae from normotensive and hypertensive rats, possibly by interfering with calcium utilization during contraction. Magnesium may be required for the contractile response to endothelin-1 and increasing magnesium may limit the vascular effects of endothelin-1 in blood vessels from DOCA-salt hypertensive rats.

Endothelin: potential role in hypertension and vascular hypertrophy

The endothelins are a family of 21-amino acid peptides that are powerful vasoconstrictors. They may also induce vascular hypertrophy. These peptides may participate through these two mechanisms in the pathogenesis of the elevation of blood pressure and/or in the maintenance of hypertension in both experimental animal models and human essential hypertension. This review presents evidence both in favor and against the involvement of endothelins in hypertension. Plasma levels of endothelin-1 are either normal or slightly elevated in experimental and human essential hypertension. Responses of blood vessels to endothelin-1 may be normal or depressed in many models of experimental hypertension and also in essential hypertension in humans. It has recently been demonstrated that endothelin content and mRNA are increased in blood vessels of deoxycorticosterone acetate-salt hypertensive rats. When endothelin receptor antagonists are administered chronically, elevation of blood pressure and development of vascular hypertrophy are blunted in this experimental model of hypertension. In contrast, spontaneously hypertensive rats do not exhibit any increase in either endothelin-1 mRNA or immunoreactive endothelin in blood vessels and fail to respond with lowering of blood pressure to longterm treatment with endothelin receptor antagonists. Blood pressure development in young spontaneously hypertensive rats is also unaffected by long-term administration of endothelin antagonists. Molecular genetic studies appear to support a genetic role of components of the endothelin system in Dahl salt-sensitive rats. In human essential hypertension, there is some evidence of activation of the endothelin system despite depressed responses of small arteries to endothelin-1 and normal circulating levels of endothelin-1 in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of vasoconstrictor agents on diacylglycerol content of normal and vasospastic canine basilar arteries in vitro

A causal or supportive relationship between 1,2-diacylglycerol (DAG) content and the maintenance of tonic vasoconstriction was sought in canine basilar arteries treated in vitro with various agents reported to increase DAG levels in other tissues (platelet-derived growth factor, vasopressin, angiotensin II, and endothelin-1) and, conversely, with agents known to activate sustained constriction (high K+, phorbol ester, hemolysate, and endothelin-1). Multiple segments from individual isolated arteries were prepared. Some segments were immediately frozen as controls and others incubated in physiological saline solution at 37 degrees C for either 5 minutes or 30 minutes in the presence or absence of different concentrations of the test materials. Segments were then quickly frozen until homogenized for lipid extraction and DAG assay. The DAG content of samples incubated up to 2 hours in physiological saline solution alone did not significantly differ from that of immediately frozen control samples. Resting DAG content expressed relative to total protein measured in each sample averaged 3.82 +/- 0.26 (standard error of the mean) pmol DAG/microgram of protein (74 samples from 37 arteries). Endothelin at 2 x 10(-7) mol/L led to a statistically significant increase in DAG content of approximately 40% of basal content at 5 and 30 minutes. A smaller increase in DAG attributable to hemolysate (approximately 25%) was statistically significant at 30 minutes, whereas vasopressin provoked a notable decrease in DAG content. The other agents had no effect. No differences in these results were noted between normal canine basilar arteries and arteries constricted in vivo by subarachnoid blood clot before isolation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chronic treatment of adult spontaneously hypertensive rats with an endothelin receptor antagonist

We previously showed that endothelin-1 expression was increased in vascular endothelium of deoxycorticosterone acetate-salt hypertensive rats, whereas in spontaneously hypertensive rats (SHR) it is similar to or less than that in normotensive rats. Treatment with the combined endothelin type A/endothelin type B receptor antagonist bosentan moderately reduced blood pressure rise and nearly completely blunted the development of vascular hypertrophy, particularly in small arteries, in the deoxycorticosterone acetate-salt hypertensive model, suggesting a paracrine role for vascular endothelin-1 in the induction of blood vessel hypertrophy in some forms of experimental hypertension. In the present study we examined the effect of chronic oral treatment for 4 weeks of 12-week-old SHR and Wistar-Kyoto rats (WKY) with 100 mg/kg per day bosentan. Blood pressure rose to hypertensive levels similarly in bosentan-treated and untreated SHR; systolic pressure of WKY was also unaffected. The wet weights of the heart, of aortic segments, and of the mesenteric arterial bed were similar in treated and untreated SHR. When coronary, renal arcuate, mesenteric, and femoral small arteries were evaluated on a wire myograph, the media width and media-to-lumen ratio were greater and the lumen diameter was smaller in vessels from SHR relative to those from WKY, except in small arteries from the renal cortex, in which the lumen was not significantly different in both strains. The media cross-sectional area of small arteries fom the four vascular beds was similar in both strains. Identical morphometric parameters were found in the four vascular beds in bosentan-treated and untreated rats of eh strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct measurements of endothelium-derived nitric oxide release by stimulation of endothelin receptors in rat kidney and its alteration in salt-induced hypertension

BACKGROUND

Stimulation of endothelin subtype B (ETB) receptors has been proposed to induce release of endothelium-derived nitric oxide (EDNO).

METHODS AND RESULTS

To obtain direct evidence of its release and its alteration in deoxycorticosterone acetate (DOCA)-salt hypertension, EDNO released from renal vessels by ET stimulation was assayed by a highly sensitive chemiluminescence method. Kidneys were isolated from DOCA-salt and control rats, and renal perfusion pressure (RPP) and EDNO (by hydrogen peroxide-luminol chemiluminescence) in the perfusate were monitored simultaneously during perfusion of ET-1, ET-3, an ETA receptor antagonist (BQ-123), and an ETB receptor agonist (BQ-3020). In control rats, ET-1 and ET-3 dose-dependently increased both RPP and NO release. Although the vasoconstricting effects of ET-1 were greater, their NO-releasing effects were comparable. The increase in NO release by ETs was inhibited by NG-monomethyl-L-arginine. After 10(-6) mol/L BQ-123 treatment, ET-1 decreased RPP and increased NO release in control kidneys. DOCA-salt rats responded to these agents with much less NO release. BQ-3020 at up to 10(-10) mol/L caused vasodilation (RPP, 10(-11) mol/L, -5.4 +/- 1.7%, P < .01) associated with increased NO release in control kidneys (+9.0 +/- 2.7 fmol.min-1.g-1 kidney wt, P < .01). However, in DOCA-salt kidneys, BQ-3020 caused renal vasoconstriction (RPP, +5.4 +/- 2.4%, P < .01 versus control) and a much smaller NO release (+1.1 +/- 0.4 fmol.min-1.g-1 kidney wt, P < .01 versus control). Northern blot analysis revealed that renal ETB mRNA was significantly decreased in DOCA-salt rat kidneys compared with controls (0.36 +/- 0.13 versus 1.00 +/- 0.23, P < .05).

CONCLUSIONS

These results suggest that ET-1 and ET-3 release EDNO via ETB receptors in renal vessels. ETB-mediated NO release was reduced in DOCA-salt rats, which may modulate renal function and thus blood pressure regulation in DOCA-salt hypertensive rats.

Increased expression of endothelin-1 gene in blood vessels of deoxycorticosterone acetate-salt hypertensive rats

We have recently shown that the content of immunoreactive endothelin-1 is increased in acid extracts from blood vessels of deoxycorticosterone acetate (DOCA)-salt hypertensive rats compared with uninephrectomized control rats. We have also found by immunohistochemistry a significant increase in immunoreactive endothelin-1 in endothelial cells of aorta and mesenteric arteries of DOCA-salt hypertensive rats. In the present study, we investigated preproendothelin-1 gene expression in blood vessels of DOCA-salt hypertensive rats and uninephrectomized control rats. Northern blot analysis using a specific 32P-labeled complementary RNA probe for rat preproendothelin-1 of 319 base pairs revealed a fourfold to fivefold increase in abundance of preproendothelin-1 messenger RNA transcripts in both aorta and mesenteric arteries from DOCA-salt hypertensive rats. Thus, increased immunoreactive endothelin-1 content in blood vessels of DOCA-salt hypertensive rats is secondary to increased preproendothelin-1 gene expression. Exaggerated expression of the preproendothelin-1 gene in mineralocorticoid hypertension may contribute to the maintenance of elevated blood pressure.

Effect of hypertension induced by nitric oxide synthase inhibition on structure and function of resistance arteries in the rat

To determine whether inhibition of generation of endothelium-derived relaxing factor or nitric oxide (NO) resulted in elevated blood pressure and its effect on resistance arteries, rats were offered NG-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NO synthase, in their drinking water. Blood pressure (BP) rose slightly from 100 +/- 2 mmHg in controls to 130 +/- 5 mmHg with 25 mg/Kg L-NAME per day and to 173 +/- 9 mmHg with 100 mg/Kg per day for 2 1/2 to 4 weeks. Rats were studied after 1-2 weeks of hypertension (BP > 150 mmHg). The concentration of cyclic guanosine monophosphate, the intracellular second messenger of NO, was significantly depressed in aorta and in the mesenteric vascular bed in L-NAME-treated rats. Mesenteric resistance arteries studied on a wire-myograph exhibited similar external and lumen diameters, whereas media width and media/lumen ratio were greater (p < 0.01). Cross-sectional area of the media was similar. Active wall tension in response to norepinephrine tended to be greater in blood vessels from L-NAME-treated rats, while responses to vasopressin and endothelin-1 were unaltered. Sensitivity to norepinephrine was significantly enhanced in L-NAME-treated rats (p < 0.001), while that to endothelin-1 and arginine8 vasopressin was similar. In conclusion, administration of an NO synthase inhibitor produces hypertension, with exaggerated media/lumen ratio in resistance arteries and enhancement of response to norepinephrine, which together with decreased NO generation may contribute to elevation of blood pressure.