Role of endothelium-formed nitric oxide on vascular responses

Ru–NO and Ru–NO2bonding linkage isomerism in cis-[Ru(NO)(NO)(bpy)2]2+/+complexes – a theoretical insight

Calculated energy profile (kcal mol⁻¹) for linkage isomers relative to the ground state structure (GS)1aprior the monoelectronic reduction.

Thrombospondin-1 supports blood pressure by limiting eNOS activation and endothelial-dependent vasorelaxation

AIMS

Thrombospondin-1 (TSP1), via its necessary receptor CD47, inhibits nitric oxide (NO)-stimulated soluble guanylate cyclase activation in vascular smooth muscle cells, and TSP1-null mice have increased shear-dependent blood flow compared with wild-type mice. Yet, the endothelial basement membrane should in theory function as a barrier to diffusion of soluble TSP1 into the arterial smooth muscle cell layer. These findings suggested that endothelial-dependent differences in blood flow in TSP1-null mice may be the result of direct modulation of endothelial NO synthase (eNOS) activation by circulating TSP1. Here we tested the hypothesis that TSP1 inhibits eNOS activation and endothelial-dependent arterial relaxation.

METHODS AND RESULTS

Acetylcholine (ACh)-stimulated activation of eNOS and agonist-driven calcium transients in endothelial cells were inhibited by TSP1. TSP1 also inhibited eNOS phosphorylation at serine(1177). TSP1 treatment of the endothelium of wild-type and TSP1-null but not CD47-null arteries inhibited ACh-stimulated relaxation. TSP1-null vessels demonstrated greater endothelial-dependent vasorelaxation compared with the wild type. Conversely, TSP1-null arteries demonstrated less vasoconstriction to phenylephrine compared with the wild type, which was corrected upon inhibition of eNOS. In TSP1-null mice, intravenous TSP1 blocked ACh-stimulated decreases in blood pressure, and both intravenous TSP1 and a CD47 agonist antibody acutely elevated blood pressure in mice.

CONCLUSION

TSP1, via CD47, inhibits eNOS activation and endothelial-dependent arterial relaxation and limits ACh-driven decreases in blood pressure. Conversely, intravenous TSP1 and a CD47 antibody increase blood pressure. These findings suggest that circulating TSP1, by limiting endogenous NO production, functions as a pressor agent supporting blood pressure.

Endothelial dysfunction: how can one intervene at the beginning of the cardiovascular continuum?

Endothelial dysfunction, characterized by impaired nitric oxide activity, constitutes an early step in the pathogenesis of atherosclerotic disease. Prospective studies have shown that impaired endothelium-dependent vasorelaxation and the vasodilatory response of coronary arteries to acetylcholine predict cardiovascular events. Microalbuminuria and estimated glomerular filtration rate, which are both deeply influenced by renal nitric oxide activity, are predictors of cardiovascular outcome and total mortality but develop at a later stage of renal impairment. Endothelial dysfunction reflects early stage renal involvement in the atherosclerotic processes. The Telmisartan versus Ramipril in renal ENdothelium DYsfunction (TRENDY) trial examined endothelial function of the renal vasculature as a therapeutic target in patients with hypertension and type 2 diabetes, but without albuminuria. The rationale was that blockade of the renin-angiotensin system (RAS) is cardio- and renoprotective at later stages of the disease, but the impact of blockade of the RAS at earlier stages of disease is unknown. The results of TRENDY indicate that the endothelial function, as assessed by basal nitric oxide activity, can be improved after RAS blockade. These data complement the results of the Diabetics Exposed to Telmisartan And enalaprIL (DETAIL) trial, which demonstrated that telmisartan and enalapril similarly decelerate the progression of overt diabetic nephropathy. The results of TRENDY are in accordance with the observed changes in peripheral circulation. Endothelium-dependent vasorelaxation could be improved with angiotensin II receptor blockers, but not with diuretics or beta-blockers, in hypertensive patients. Intervention at the beginning of the renal and cardiovascular continuum offers the opportunity to prevent the fatal development towards renal and cardiac failure.

Nitric oxide in subarachnoid haemorrhage and its therapeutics implications

BACKGROUND

After the discovery that nitric oxide (NO) plays a major role in the regulation of vascular tone, this substance moved into the focus of interest with regard to vasospasm after subarachnoid haemorrhage (SAH). A multitude of interactions were discovered and some concepts of therapeutic intervention were developed.

METHOD

The present review is based on a Medline search with the terms "nitric oxide" and "subarachnoid haemorrhage".

FINDINGS

SAH and particularly liberated oxyhaemoglobin sequestrate the physiologically produced NO. Reactivity to NO appears to be principally preserved. As other types of injury, SAH leads to induction of inducible NO synthase (iNOS). The NO produced by this pathway cannot compensate for the lack of the physiological NO and may even lead to tissue damage by oxidative stress. Experimental therapeutic attempts use stimulation of NO production and delivery of NO donors. NO donors were also used in some small clinical trials. A final assessment of efficacy and safety is not yet possible.

CONCLUSION

NO physiology and pathophysiology are important in the genesis of vasospasm after subarachnoid haemorrhage. NO directed therapeutic strategies enlarge the spectrum of available instruments, but complete elimination of the problem of vasospasm cannot be expected.

Defective acute inflammation in Crohn's disease: a clinical investigation

BACKGROUND

The cause of Crohn's disease has not been mechanistically proven. We tested the hypothesis that the disease is a form of immunodeficiency caused by impaired innate immunity.

METHODS

We investigated inflammatory responses in patients and controls by quantifying neutrophil recruitment and cytokine production after acute trauma, interleukin 8 secretion by cultured monocyte-derived macrophages after exposure to inflammatory mediators, and local inflammatory and vascular changes in response to subcutaneous injection of heat-killed Escherichia coli.

FINDINGS

In patients with Crohn's disease, trauma to rectum, ileum, or skin led to abnormally low neutrophil accumulation (differences from healthy individuals of 79%, n=8, p=0.0003; 57%, n=3, p=0.05; 50%, n=13, p<0.0001, respectively) and lower production of proinflammatory interleukin 8 (63%, n=7, p=0.003; 63%, n=3, p=0.05; 45%, n=8, p<0.0001) and interleukin 1beta (50%, n=8, p=0.0005). Interleukin 8 secretion by cultured macrophages was reduced after exposure to acute wound fluid (38%, n=50, p<0.0001), C5a (48%, n=41, p=0.0005), or tumour necrosis factor alpha (52%, n=27, p<0.0001). Local inflammatory reaction to inoculation with E coli was attenuated, as quantified by changes in bloodflow (ileal disease 50%, n=6, p=0.01; colonic disease 77%, n=6, p=0.0003). This response was mediated by nitric oxide in controls, was increased by sildenafil in patients, and was not related to CARD15 genotype.

INTERPRETATION

In Crohn's disease, a constitutionally weak immune response predisposes to accumulation of intestinal contents that breach the mucosal barrier of the bowel wall, resulting in granuloma formation and chronic inflammation. Polymorphisms in CARD15 do not underlie this phenotype, but incapacitate the NOD2 pathway that can compensate for impairment of innate inflammation. Current treatment of secondary chronic inflammation might exaggerate the underlying lesion and promote chronic disease.

Effects of high sodium intake diet on the vascular reactivity to phenylephrine on rat isolated caudal and renal vascular beds: Endothelial modulation

High salt intake is involved in the genesis of hypertension and vascular changes in salt-sensitive patients. Although many mechanisms have been proposed, the underlying mechanisms of these alterations in healthy rats are not completely elucidated. The aim of this study was to investigate if male Wistar rats fed a high salt diet, NaCl 1.8% in drinking water for 4 weeks, develop changes in the pressor reactivity of isolated tail and renal vascular beds. Salt treatment increased mean arterial pressure (SALT = 124 +/- 2.2 vs. CT = 111 +/- 3.9 mmHg; p < 0.01) and urinary sodium excretion in the absence of changes in sodium plasma levels. Pressor reactivity was generated in isolated tail and kidney vascular beds as dose-response curves to phenylephrine (PHE = 0.01 to 300 microg). SALT increased the reactivity (E(max): SALT = 378 +/- 15.8 vs. CT = 282 +/- 10 mmHg; p < 0.01) without changing the sensitivity (pD(2)) to PHE in the tail vascular bed. However, these parameters did not change in the renal bed. In subsequent studies on the isolated caudal vascular bed, we found that endothelial damage, but not L-NAME (100 microM) or indomethacin (10 microM), abolished the increment in E(max) to PHE induced by SALT. On the other hand, losartan (100 microM) reduced E(max) in SALT to CT values. Additionally, local angiotensin-converting enzyme activity in segments from tail artery increased by 95%. In conclusion, 4 weeks of high salt diet increases blood pressure and induces specific territorial vascular changes in response to PHE. Results also suggest that the increment in E(max) in the tail vascular bed from SALT rats was endothelium-dependent and was mediated by the activation of the local renin-angiotensin system.

Redox activity associated with the maturation and capacitation of mammalian spermatozoa

As rat spermatozoa undergo epididymal maturation, they acquire the ability to exhibit a spontaneous burst of luminol-peroxidase-dependent chemiluminescence when released into a simple, defined culture medium. This activity was suppressed by inhibitors of plasma membrane redox systems such as diphenylene iodonium, p-chloromercuribenzenesulfonic acid, and capsaicin, but was resistant to inhibition by resiniferatoxin and rotenone. The luminol-peroxidase signal was dependent on the presence of bicarbonate, enhanced by the substitution of fructose for glucose, and severely suppressed by desferoxamine, superoxide dimutase, and catalase. Both L- and D-arginine were stimulatory, suggesting the involvement of *NO in this spontaneous chemiluminescence activity. The L-arginine-dependent, but not the D-arginine-dependent, activity was significantly suppressed by an inhibitor of nitric oxide synthase (N(G)-nitro-L-arginine methyl ester). L- and D-arginine could also stimulate redox activity observed in immature caput epididymal cells, but only after prolonged incubation. The inhibitory effects of uric acid and ascorbate suggested the chemiluminescence signal might be induced by peroxynitrite. This conclusion was supported by confocal imaging of the cells following treatment with 4-amino-5-methylamino-2',7'-difluorofluorescein. Stimulation or suppression of the redox activity detected by luminol-peroxidase led to corresponding changes in the ability of the spermatozoa to exhibit acrosomal exocytosis, indicating that this pathway is of fundamental biological significance.

Nitric oxide modulates pro- and anti-inflammatory cytokines in lipopolysaccharide-activated macrophages

BACKGROUND

Sepsis is a serious and life-threatening syndrome that occurs in intensive care unit patients. Lipopolysaccharide (LPS) has been implicated as one of major causes of sepsis. Nitric oxide (NO) and cytokines are involved in sepsis-induced inflammatory responses. This study is aimed at evaluating the effects of NO on the modulation of pro- and anti-inflammatory cytokines in LPS-activated macrophages and its possible mechanism.

METHODS

N-Monomethyl arginine (NMMA), an inhibitor of NO synthase, was used in this study to suppress NO production. Mouse macrophage-like Raw 264.7 cells were exposed to LPS, NMMA, or a combination of NMMA and LPS. Cell viability was determined by the colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-di-phenyltetrazolium bromide assay. The amounts of nitrite, an oxidative product of NO, in the culture medium were quantified according to the Griess reaction method. Enzyme-linked immunosorbent assay and reverse-transcriptase polymerase chain reaction were carried out to determine the expression of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta, and IL-10 in macrophages.

RESULTS

Exposure of macrophages to LPS, NMMA, and a combination of NMMA and LPS for 24 hours did not affect cell viability. LPS significantly increased the amounts of nitrite in macrophages (p < 0.01). Treatment with NMMA decreased LPS-enhanced nitrite (p < 0.01) in a concentration-dependent manner. Analyses of enzyme-linked immunosorbent assays and reverse-transcriptase polymerase chain reaction revealed that LPS significantly induced TNF-alpha, IL-1 beta, and IL-10 proteins and mRNA (p < 0.01). A combined treatment with NMMA and LPS significantly blocked LPS-induced TNF-alpha and IL-1 beta (p < 0.01), but synergistically enhanced LPS-induced IL-10 (p < 0.05) protein and RNA.

CONCLUSION

This study has shown that NO suppression can inhibit LPS-induced TNF-alpha and IL-1 beta but enhance IL-10, and the modulation occurs at a pretranslational level.

Role of endogenous endothelin on coronary flow in health and disease

The role of the endothelium in the control of coronary flow has been demonstrated. Results of recent studies, both on animals and on humans, suggest that endogenous endothelin also plays an important role in basal coronary tone. Disease processes such as ischaemia-reperfusion injury, congestive heart failure, hypertension and atherosclerosis may be contributed to by an imbalance in, or excess of, release of endothelin. With the discovery of newer endothelin antagonists and endothelin converting enzyme inhibitors, especially with fewer hepatic side effects, there is the potential for much future research into novel therapeutic management of these common cardiovascular disorders.

Diabetes and endothelial dysfunction: a clinical perspective

The main etiology for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. A hypothesis for the initial lesion of atherosclerosis is endothelial dysfunction, defined pragmatically as changes in the concentration of the chemical messengers produced by the endothelial cell and/or by blunting of the nitric oxide-dependent vasodilatory response to acetylcholine or hyperemia. Endothelial dysfunction has been documented in patients with diabetes and in individuals with insulin resistance or at high risk for developing type 2 diabetes. Factors associated with endothelial dysfunction in diabetes include activation of protein kinase C, overexpression of growth factors and/or cytokines, and oxidative stress. Several therapeutic interventions have been tested in clinical trials aimed at improving endothelial function in patients with diabetes. Insulin sensitizers may have a beneficial effect in the short term, but the virtual absence of trials with cardiovascular end-points preclude any definitive conclusion. Two trials offer optimism that treatment with ACE inhibitors may have a positive impact on the progression of atherosclerosis. Although widely used, the effect of hypolipidemic agents on endothelial function in diabetes is not clear. The role of antioxidant therapy is controversial. No data have been published regarding the effects of hormonal replacement therapy on endothelial dysfunction in postmenopausal women with type 2 diabetes.

Nitric oxide: a review for veterinary surgeons

Nitric oxide (NO) is an endogenous gas that serves as a biologic messenger in many physiologic processes including neurotransmission, blood-pressure control, the immune system's ability to kill tumor cells, and wound healing. NO is produced after oxidation of L-arginine by a family of nitric oxide synthase (NOS) enzymes. Two of the NOS enzymes are present continuously and are thereby termed constitutive NOS. One of the enzymes, inducible NOS, is not typically expressed in resting cells and is induced by various substances including endotoxin, some cytokines, and microbial products. Thus, NO often has paradoxical activities. When NO is over- or underproduced, it can result in potentiation of disease states with disastrous results. This review discusses the biochemistry of NO, its functions in normal and disease states, and therapy for modulating NO production in disease states.

Increase in neurogenic nitric oxide metabolism by endothelin-1 in mesenteric arteries from hypertensive rats

We investigated, in mesenteric arteries from hypertensive rats (SHRs), the possible changes in neurogenic nitric oxide (NO) release produced by endothelin-1 (ET-1), and the mechanisms involved in this process. The contractile response induced by electrical field stimulation (EFS; 200 mA, 0.3 ms, 1-16 Hz, for 30 s) in deendotheliumized mesenteric segments was abolished by tetrodotoxin and phentolamine. The NO synthase inhibitor N(G)-nitro-L-arginine (L-NAME, 10 microM) increased the contractions caused by EFS. ET-1 enhanced the contraction induced by EFS, which was unaltered by the subsequent addition of L-NAME. The ETA antagonist-receptor BQ-123 (1 microM) inhibited the effect of ET-1 on EFS response, whereas the ETB antagonist-receptor BQ-788 (3 microM) partially blocked it, and the subsequent addition of L-NAME restored the contractile response in both cases. SOD (25 unit/ml) decreased the response to EFS, and the subsequent addition of L-NAME increased this response. ET-1 did not modify the decrease in EFS response induced by SOD, and the addition of L-NAME increased the response. None of these drugs altered the response to exogenous noradrenaline (NA) or basal tone except SOD, which increased the basal tone, an effect blocked by phentolamine (1 microM). In arteries preincubated with [3H]NA, ET-1 did not modify the tritium efflux evoked by EFS, which was diminished by SOD. ET-1 did not alter basal tritium efflux, whereas SOD significantly increased the efflux. These results suggest that EFS of SHR mesenteric arteries releases neurogenic NO, the metabolism of which is increased in the presence of ET-1 by the generation of superoxide anions.

Nitric oxide generation in a rat model of acute portal hypertension

OBJECTIVE

To document blood nitric oxide concentrations in the portal vein and systemic circulation in a rat model of acute portal hypertension and compare values with a control group and a sham surgical group.

ANIMALS

30 rats; 10 controls (group 1), 10 sham surgical (group 2), and 10 rats with surgically induced acute portal hypertension (group 3).

PROCEDURE

Following induction of anesthesia, catheters were placed surgically in the carotid artery, jugular, and portal veins of group 2 and 3 rats and in the carotid artery and jugular vein of group 1 rats. Baseline heart and respiratory rates, rectal temperature, and vascular pressure measurements were obtained, and blood was drawn from all catheters for baseline nitric oxide (NO) concentrations. Acute portal hypertension was induced in the group 3 rats by tying a partially occluding suture around the portal vein and a 22-gauge catheter. The catheter was then removed, resulting in a repeatable degree of portal vein impingement. After catheter placement, all variables were remeasured at 15-minute intervals for 3 hours.

RESULTS

Blood nitric oxide concentrations were greater in all vessels tested in group 3 than in group 2 rats.

CONCLUSIONS AND CLINICAL RELEVANCE

Acute portal hypertension in this experimental model results in increased concentrations of NO in the systemic and portal circulation. On the basis of information in the rat, it is possible that increased NO concentrations may develop in dogs following surgical treatment of congenital portosystemic shunts if acute life-threatening portal hypertension develops. Increased NO concentrations may contribute to the shock syndrome that develops in these dogs.

Role of K+ channels and sodium pump in the vasodilation induced by acetylcholine, nitric oxide, and cyclic GMP in the rabbit aorta

The endothelium-dependent relaxation caused by acetylcholine (ACh) in rabbit aorta segments was reduced by the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methyl ester and by blockade of: Na+ pump with ouabain, large-conductance Ca2+-activated K+ (BK(Ca)) channels with charybdotoxin (ChTx), or voltage-dependent K+ (Kv) channels with 4-aminopyridine (4-AP). ACh relaxation was unaltered by glibenclamide, apamin, and Ba2+, blockers of ATP-sensitive K+ channels, small-conductance Ca2+-activated K+ channels, and inward rectifier K+ channels, respectively. The relaxation induced by exogenous NO and 8-bromocyclic GMP (8-BrcGMP) was similar in intact and endothelium-denuded segments, and it was reduced or unaltered by the same drugs used in the case of ACh. However, a 4-AP concentration 20-fold higher was necessary to reduce exogenous NO relaxation. These data suggest a resemblance in the mechanisms implicated in the relaxation elicited by ACh, exogenous NO, and 8-BrcGMP. Therefore, the relaxation caused by ACh is mainly mediated by endothelial NO, which in turn, enhances cGMP levels; this messenger appears to be the major one responsible for the smooth muscle cell hyperpolarization in the relaxation elicited by ACh, which is mediated by activation of the Na+ pump and ChTx- and 4-AP-sensitive K+ channels, likely BK(Ca) and Kv channels.

Impairment of endothelial relaxations by glycosylated human oxyhemoglobin depends on the oxidative state of the heme group

While nanomolar met- or cyanomethemoglobin, either non-glycosylated or glycosylated, did not alter endothelial function, glycosylated oxyhemoglobin induced contractile responses and caused an impairment of endothelium-dependent relaxations in rat aortic segments. The vascular effects induced by glycosylated oxyhemoglobin were prevented by superoxide dismutase. Furthermore, glycosylated oxyhemoglobin produced higher amounts of superoxide anions than other hemoglobin derivatives. These results suggest that glycosylated hemoglobin requires the existence of a functional heme group containing iron in ferrous state to interfere with the endothelial function at nanomolar concentrations. This effect is mediated by generation of superoxide anions.

Effect of age on the vasorelaxation elicited by cromakalim. Role of K+ channels and cyclic GMP

The objective of this study was to investigate whether age induces changes on vasodilator response induced by cromakalim, an ATP-sensitive K+ (K(ATP)) channel opener, as well as the underlying mechanism involved in this possible alteration. For this purpose, aortic segments from young (3-5 months) and old (3 years) rabbits were used, which were precontracted with noradrenaline (NA, 1 microM). The vasodilator response induced by cromakalim (0.01-100 microM) was reduced in intact segments from old rabbits, and endothelium removal reduced and did not modify this effect in young and old animals, respectively. In both groups of animals, glibenclamide (10 microM), a blocker of K(ATP) channels, significantly reduced the response elicited by cromakalim, which was not modified by the large conductance Ca2+-activated K+ channel blocker charybdotoxin (ChTX, 0.4 microM). Acetylcholine (ACh, 10 microM) and sodium nitroprusside (SNP, 100 microM) induced a lesser vasodilator effect in aortic segments from old compared with young rabbits. In segments precontracted with NA, 10 microM ACh or 100 microM SNP similarly increased cGMP levels in both groups of animals. However, basal cGMP level was reduced in segments from old rabbits. Incubation with 8-bromo-cGMP (100 microM) increased the response induced by cromakalim in both groups of animals, reaching similar maximum values in young and old rabbits. The response induced by cromakalim plus 8-bromo-cGMP was markedly decreased by glibenclamide and unmodified by ChTx in both types of animals. These results suggest that aging decreases the vasodilator response to cromakalim, mechanism in which appears to be involved the maintained low cGMP levels observed in old rabbits, and that this messenger modulates the degree of K(ATP) channel activation.

Positive inotropic, negative chronotropic, and coronary vasoconstrictor effects of acetylcholine in isolated rat hearts: role of muscarinic receptors, prostaglandins, protein kinase C, influx of extracellular ca2+, intracellular Ca2+ release, and endothelium

The involvement of nitric oxide (NO), muscarinic receptors, prostaglandins, calcium influx via slow calcium channels, Ca2+ release from intracellular stores, protein kinase C, and endothelium in the positive inotropic, negative chronotropic, and coronary vasoconstrictor effects of acetylcholine (ACh) has been investigated in isolated rat hearts. The perfusion of hearts with ACh (10(-7), 5 x 10(-7), and 10(-6) M) produced marked decreases in heart rate and coronary flow and a marked increase in contractile force. Similar effects have been observed during the perfusion of hearts with ACh in the presence of Nomega-nitro-L-arginine methyl ester (L-NAME), which is an inhibitor of NO synthesis. The positive inotropic, negative chronotropic, and coronary vasoconstrictor effects of ACh were abolished by muscarinic receptor blocker atropine. In hearts pretreated with cyclooxygenase inhibitor indomethacin, ACh significantly decreased heart rate but did not significantly affect coronary flow and contractile force. In the presence of calcium channel antagonist verapamil or protein kinase C inhibitor staurosporine, ACh produced a significant drop in heart rate but did not significantly affect coronary perfusion pressure and force of contraction. In the presence of the inhibitor of the release of Ca2+ from intracellular stores dantrolene sodium, ACh produced a significant increase in coronary perfusion pressure and a marked decline in heart rate, but did not significantly affect force of contraction. Furthermore, the disruption of endothelium by perfusing the hearts with saponin abolished the vasoconstrictor effect of ACh but did not alter negative chronotropic and positive inotropic effect. Our results suggest that ACh causes vasoconstrictor, negative chronotropic, and positive inotropic effects in isolated rat hearts. Cardiac effects of ACh are related to muscarinic receptor activation, and prostaglandins modulate ACh-induced vasoconstriction and positive inotropy. Our data also suggest that protein kinase C and calcium influx from extracellular source may be responsible for the vasoconstrictor and positive inotropic effect of ACh. The calcium release from intracellular stores may mediate the positive inotropic effect, and the vasoconstrictor effect of ACh depends on an intact endothelium.

The relaxation effects of ginseng saponin in rabbit corporal smooth muscle: is it a nitric oxide donor?

OBJECTIVE

To determine whether crude extracts of ginseng saponin (GCS), containing the active ingredients from Panax ginseng and used as an aphrodisiac in oriental countries, relax corpus cavernosal smooth muscle in the rabbit.

MATERIALS AND METHODS

Corpus cavernosal strips were prepared from rabbit penises. Isometric tension changes, recorded with a pressure transducer, in response to various drugs and electrical stimulation were assessed in an organ chamber, after active muscle tone had been induced by 10 micromol/L phenylephrine.

RESULTS

GCS (0.2-8.0 mg) relaxed the smooth muscle of rabbit corpus cavernosum (SMRCC) pre-contracted with phenylephrine in a dose-dependent manner. GCS at 0.75 mg significantly enhanced the relaxation of SMRCC induced by electrical field stimulation. The relaxation induced by 0.2-8.0 mg GCS was significantly attenuated by atropine (1 micromol/L), methylene blue (100 micromol/L) and N-omega-nitro-L-arginine methyl ester (L-NAME, 10 micromol/L). However, there was no significant difference in the attenuation of GCS-induced relaxation of SMRCC by adding vasoactive intestinal peptide antagonists or indomethacin. In addition, the decreasing rate of GCS-induced relaxation of SMRCC by methylene blue and L-NAME was greater than that by atropine. L-arginine (10 mmol/L) reversed the inhibitory effect induced by L-NAME (1 mmol/L) on the attenuation of GCS-induced relaxation.

CONCLUSIONS

These data suggest that GCS, as a nitric oxide donor, induces the relaxation of SMRCC through the L-arginine/nitric oxide pathway. For the clinical application of ginseng saponin, further studies are required to clarify the active subfraction(s) of GCS.

Role of endogenous endothelin in the regulation of basal coronary tone in the rat

1. Coronary vascular tone is a vital factor that regulates the delivery of oxygen to cardiac muscle. We tested the hypothesis that basal coronary tone may depend on the release of an endogenous vasoconstrictor peptide, endothelin (ET). 2. Using an isolated, Krebs solution-perfused rat heart we measured the changes in coronary flow following the administration over a 30 min period of the ET antagonists Ro61-0612 (mixed ETA/ETB), PD155080 (ETA) and BQ788 (ETB). 3. In a second series of experiments, hearts were randomly assigned to perfusion with plain Krebs solution, or with Krebs solution to which L-NAME and/or indomethacin had been added. The effect on coronary flow following the addition of Ro61-0612 was then measured. 4. Perfusion with Ro61-0612 (10-4 M) alone increased coronary flow by 57.8 % vs. control (P = 0.00001). PD155080 (10-4 M) increased coronary flow by 28.9 % (P = 0.009), whereas BQ788 had no effect on coronary flow. 5. In the second series of experiments, Ro61-0612 increased coronary flow by 6.6 +/- 0.8 ml min-1 in hearts perfused with plain Krebs solution, by 3.8 +/- 0.8 ml min-1 in hearts to which both L-NAME and indomethacin had been added, by 3.3 +/- 0.7 ml min-1 in hearts to which L-NAME had been added, and by 6. 9 +/- 0.5 ml min-1 in hearts to which indomethacin had been added to the Krebs buffer. 6. In hearts perfused with Krebs solution alone, nitric oxide (NO) release into the coronary sinus increased from 219. 8 to 544.9 pmol min-1 g-1 following the addition of Ro61-0612 (P = 0. 06). There was no detectable release of NO from hearts perfused with L-NAME alone or in combination with indomethacin either before or after the addition of Ro61-0612. 7. We conclude that endogenous ET plays a role in coronary tone mediated via ETA receptors. This vasodilatation is partially due to an increase in endogenous NO release. However, a significant vasodilatation is still seen following the inhibition of NO synthesis. We propose that basal coronary tone depends on a balance between the endogenous release of vasodilators such as NO and vasoconstrictors such as ET.

Evidence that angiotensin II, endothelins and nitric oxide regulate mitogen-activated protein kinase activity in rat aorta

We measured the activity of mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, in rat aortic strips with or without endothelium, and examined effects of angiotensin receptor antagonists, endothelin receptor antagonists and nitric oxide (NO)-related agents. Endothelium removal produced an activation of MAP kinase activity in the strips, whereas the enzyme activity was not affected in the adventitia. The MAP kinase activation was inhibited by either the angiotensin AT1 receptor antagonist losartan or the endothelin ETA receptor antagonist BQ 123. The combination of both antagonists caused an additive inhibition. The angiotensin AT2 receptor antagonist PD 123,319 and the endothelin ETB receptor antagonist BQ 788 did not affect the MAP kinase activation. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) caused an activation of MAP kinase in the endothelium-intact aorta and the MAP kinase activation was inhibited by losartan or BQ123. The NO releaser nitroprusside inhibited the MAP kinase activation induced by endothelium removal or angiotensin II. These results suggest that even in isolated arteries, NO of endothelial origin tonically exert MAP kinase-inhibiting effects and endogenous angiotensin II and endothelins in the media are tonically released to cause MAP kinase-stimulating effects in medial smooth muscle.

Investigations into the role of nitric oxide and the large intracranial arteries in migraine headache

Previous studies suggest that nitric oxide (NO) is involved in headaches induced by i.v. infusion of the vasodilator and NO donor glyceryl trinitrate (GTN) in healthy subjects. Extending these studies to sufferers of migraine without aura, it was found that migraineurs experienced a stronger headache than non-migraineurs. In addition, most migraineurs experienced a delayed migraine attack at variable times (mean 5.5 h) after GTN provocation. This biphasic headache response in migraineurs may be linked to hypersensitivity in the NO-cGMP pathway. Thus, compared to controls, migraineurs were found to be more sensitive to GTN-induced intracranial arterial dilatation, which is known to be mediated via liberation of NO and subsequent synthesis of cGMP Furthermore, histamine infusions in migraineurs induced headache responses and intracranial arterial responses resembling those induced by GTN in migraineurs. Histamine is known to liberate NO from the endothelium via stimulation of the H1 receptor, which is present in the large intracranial arteries in man. Because both immediate histamine-induced headache and intracranial arterial dilatation and delayed histamine-induced migraine are blocked by H1-receptor blockade, a likely common pathway for GTN and histamine-induced headaches/migraines and intracranial arterial responses may be via activation of the NO-cGMP pathway. The delay in the development of these experimental migraines may reflect activation of multiple physiological processes. The intracranial arteries of migraineurs were found supersensitive to the vasodilating effect of GTN (exogenous NO). This relates to clinical findings suggesting dilatation of the large intracranial arteries on the headache side during spontaneous migraine attacks. The function of arterial regulatory mechanisms involving NO in migraine was therefore studied. In peripheral arteries, no endothelial dysfunction of NO was found and cardiovascular and intracranial arterial sympathetic function was normal. A mild parasympathetic dysfunction may be involved and may, via denervation supersensitivity, be responsible for the observed supersensitivity to NO. Another possibility is that NO initiates a perivascular neurogenic inflammation with liberation of vasoactive peptides. NO also mediates a variety of other physiological phenomena. One of these, the pain-modulating effect observed in animals, was evaluated in a human study using GTN infusion and measurements of pain thresholds. No definite effects of GTN were demonstrated. The precise mechanisms involved in NO-triggered migraines and which part of the NO-activated cascade that is involved remain to be determined. The possibilities for pharmacological stimulation and/or inhibition of several steps of the NO-activated cascade increase rapidly and soon may be available for human studies.

Impaired blood flow response following pressure load in diabetic patients with cardiac autonomic neuropathy

OBJECTIVE

An impaired blood flow response is associated with an increased risk of developing decubitus ulcers. This study investigated whether diabetic patients with autonomic neuropathy show an impaired blood flow response following pressure load, compared with healthy controls.

DESIGN

Before-after trial.

SETTING

University hospital.

PATIENTS

Eighteen patients with type I diabetes and autonomic neuropathy, and 15 healthy volunteers.

RESULTS

The blood flow response starts with a latency period, followed by a temperature increase (described by the "time constant"). The blood flow response in both groups showed significant (p < .01) differences. In diabetic patients, the latency time was 312 +/- 221 sec, the time constant was 339 +/- 149 sec, and the recovery time was 538 +/- 184 sec. In controls, latency time was 83 +/- 47 sec, time constant was 79 +/- 69 sec, and recovery time was 162 +/- 103 sec. The velocity of the blood flow response decreased with increasing duration of diabetes mellitus (p = .02).

CONCLUSIONS

Diabetic patients with autonomic neuropathy show an impaired blood flow response after pressure relief. This finding suggests that these patients have an increased risk of developing decubitus ulcers.

Role of vascular nitric oxide in physiological and pathological conditions

This review describes the ability of certain diseases, such as essential hypertension, atherosclerosis, angina, and vasospasm, to reduce vascular nitric oxide (NO) formation or to increase its metabolism. In contrast, others, such as hypotension, sepsis, stroke, myocardial depression, and inflammatory responses, increase NO synthesis. The mechanism implicated in the changes in the formation and metabolism of NO are described. To prevent or treat these pathological processes, in which a deficiency in vascular NO formation plays a causative role, NO may be provided through methods such as direct NO administration or indirect NO supply through either NO donors or L-arginine, which facilitates NO formation.

Inhibition of nitric oxide does not affect reperfusion-induced myocardial injury, but it prevents lipid peroxidation in the isolated rat heart

To examine if inhibition of nitric oxide (NO) synthesis influences myocardial ischemia-reperfusion injury, male Sprague Dawley rats were administered the NO synthesis inhibitor N -nitro-L-arginine methyl ester (L-NAME, 10 mg/kg, i.p.) or saline 6 hours prior to excising the heart and aorta. Aortic ring contractile response to norepinephrine (NE) was more pronounced and relaxation in response to acetylcholine was abolished in L-NAME-treated group (P<0.05 vs. saline-treated group), indicating inhibition of NO synthesis in the vascular tissues. In the isolated perfused Langendorff hearts, force of cardiac contraction (FCC) and coronary perfusion pressure (CPP) were higher and coronary flow was lower in the L-NAME-treated group, again suggesting inhibition of NO synthesis. Global ischemia (40 min) followed by reperfusion (30 min) resulted in a decrease in FCC and coronary flow and an increase in CPP in all hearts. Myocardial CK also decreased similarly in all hearts. However, ischemia-reperfusion-induced decline in myocardial superoxide dismutase (SOD) activity and increase in malondialdehyde were prevented in the L-NAME-treated group (P<0.01 vs. saline-treated hearts). Thus treatment with L-NAME with resultant inhibition of NO synthesis does not affect ischemia-reperfusion-induced cardiac dysfunction and injury in the isolated rat hearts, although the reduction in SOD activity and the rise in lipid peroxidation following reperfusion are attenuated.

A possible role for nitric oxide in the regulation of human ureteral smooth muscle tone in vitro

There is ample evidence that nitric oxide (NO) is an important neurotransmitter in many tissues of the urogenital tract. The aim of the present study was to examine the possible role of NO in ureteral relaxation. Human ureteral rings were mounted in organ bath chambers and precontracted in KCl. Increasing doses of the NO donor linsidomine (SIN-1) were added with and without prior blockade of the NO/cGMP pathway by methylene blue and protein kinase (PK) inhibitors Rp-8-pCPT-cGMPS and RP-8-CPT-cAMPS. Electrical filed stimulation (EFS) was done before and after incubation with L-NOARG (NG-nitro-L-arginine) and TTX (tetratodoxin). For detection of neuronal NO synthase (NOS), ureters were stained immunohistochemically. Ureteral strips were dose dependently relaxed by SIN-1; preincubation with methylene blue and protein kinase G inhibitor significantly reduced the SIN-1-induced relaxations. No effects of L-NOARG and TTX on EFS-induced tone alterations were found. NOS-positive neuronal axons and nerve-ending-like structures were found in the muscular layers. Our in vitro findings suggest that ureteral relaxation may involve the NO pathway.

The mechanism of relaxation induced by atrial natriuretic peptide in the porcine renal artery

1. The mechanisms underlying the relaxation of the porcine renal artery induced by atrial natriuretic peptide (ANP) were investigated, using front-surface fluorimetry with fura-2 and receptor-coupled permeabilization by alpha-toxin. 2. ANP decreased the cytosolic Ca2+ concentration ([Ca2+]i) and tension during the contraction induced by a high external K+ solution, in a concentration-dependent manner. This ANP-induced decrease in [Ca2+]i during the contraction induced by high K+ solution was composed of two phases, an initial rapid phase, followed by a maintenance phase. The initial rapid decrease in [Ca2+]i, but not the maintained decrease in [Ca2+]i, was inhibited when the tissue was treated with thapsigargin, a selective Ca2+ pump inhibitor of the sarcoplasmic reticulum. When the tissues were treated with thapsigargin and external Ca2+ was replaced by Ba2+, which cannot be transported by the Ca2+ pump, ANP did not induce a decrease in [Ba2+]i, even though the elevation of tension induced by Ba2+ was strongly inhibited. 3. In the absence of extracellular Ca2+, ANP inhibited the release of Ca2+ from the intracellular store induced by noradrenaline (NA). 4. The [Ca2+]i (abscissa scale)-tension (ordinate scale) relationship observed during the contraction induced by various concentrations of high external K+ solution was shifted downwards by the addition of 10(-8) M ANP, indicating that, at any given [Ca2+]i, the tension generated by high K+ solution was considerably inhibited by the addition of 10(-8) M ANP. The [Ca2+]i-tension curve of the contraction obtained by the cumulative application of external Ca2+ (0-3.75 mM) during depolarization with 118 mM K+ solution was shifted to the left by 3 x 10(-7) M NA. This NA-induced [Ca2+]i-tension relationship was shifted to the right by 10(-8) M ANP, indicating that the ANP-induced reduction of Ca(2+)-sensitivity operates during the contraction induced by NA. 5. In alpha-toxin-permeabilized preparations, ANP induced relaxation of tissues precontracted with a mixture of 3 x 10(-7) M Ca2+, 10(-5) M guanosine 5'-triphosphate (GTP) and 10(-6) M NA. Thus a component of ANP-induced relaxation took place by way of a reduction in the Ca2+ sensitivity of the myofilaments, independent of changes in [Ca2+]i. 6. These results indicate that ANP induces relaxation of the porcine renal artery by: (1) reducing [Ca2+]i mainly via the activation of the Ca2+ pumps located on the sarcoplasmic reticulum and sarcolemma, as well as via inhibition of agoinist-induced release of Ca2+ from the intracellular store; and (2) decreasing the Ca(2+)-sensitivity of the contractile elements.

Increasing nitric oxide production improves survival in experimental hemorrhagic shock

The purpose of this study was to evaluate the importance of nitric oxide (NO) upon outcome following hemorrhagic shock. L-Arginine, an NO precursor, and L-NMMA, an inhibitor of NO synthesis, were added to resuscitation in a prospective, randomized, and double-blinded experimental model, and the effects upon blood pressure and survival were measured.

METHODS

60 Sprague-Dawley rats were anesthetized and subjected to phlebotomy to induce hemmorrhagic shock. After a 45 min shock period, animals were resuscitated with either lactated Ringer's alone (control), L-NMMA in lactated Ringer's or L-arginine in lactated Ringer's. Blood pressure was monitored, and animals were observed for survival. As an additional control experiment, 15 additional animals underwent the same protocol, but underwent sham shock, i.e. were not haemorrhaged.

RESULTS

L-NMMA increased blood pressure transiently following sham shock, but increased blood pressure to a greater extent and for a longer duration following hemorrhage. However, L-NMMA had no effect upon survival. L-Arginine had no measurable effect upon blood pressure, but significantly increased survival.

CONCLUSION

NO may play an important role following hemorrhage. The effectiveness of L-NMMA as a pressor suggests that NO contributes to hypotension following hemorrhage. However, reversing hypotension with L-NMMA did not improve survival in this model. In contrast, L-arginine did not further lower blood pressure, but had significant survival benefit. This suggests a possible protective effect of NO after hemorrhage, perhaps by improving the distribution of capillary blood flow and/or by decreasing platelet aggregation and leukocyte adhesion within the microcirculation.

Alpha-atrial natriuretic peptide-induced attenuation of vasoconstriction in the fetal circulation of the human isolated perfused placenta

In order to examine the effect of alpha-ANP on fetal placental vascular tone, single placental lobules were bilaterally perfused and fetal inflow pressure recorded. The placental vasculature was sub-maximally pre-constricted by infusion of the nitric oxide synthase inhibitor N omega-nitro-L-arginine (NOLA) or the thromboxane A2-mimetic U46619. In the presence of continuous infusion of 59.3 mumol/l NOLA, producing a mean pressure increase of 43.7 +/- 1.7 mmHg (n = 8, mean +/- SEM), alpha-ANP (10.7 to 325 nmol/l) produced significant pressure decreases (P < 0.05). In separate experiments (U46619 was either infused at concentrations (4.8 to 21.4 nmol/l) to produce a mean pressure increase (50.1 +/- 2.6 mmHg, n = 10) similar to that produced by NOLA infusion or was infused at a concentration (28.5 nmol/l) that produced a significantly higher pressure increase (104 +/- 15 mmHg), infusion of 1 mumol/l alpha-ANP significantly reduced perfusion pressure. However, 100 nmol/l alpha-ANP or less had no significant effect (n = 4-7). These results indicate that alpha-ANP attenuates NOLA-induced and U46619-induced vasoconstriction in the human placenta, but at concentrations higher than those in fetal or maternal plasma.

Influence of age on the relaxation induced by nifedipine in aorta from spontaneously hypertensive and Wistar Kyoto rats

1. Nifedipine induces relaxation in aortic segments from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) of 5-week-, 3-month-, 6-month- and 1.5-year-old precontracted with 50 mM K+ or 0.1 microM noradrenaline (NA). 2. In WKY rat segments precontracted with K+, nifedipine relaxation was reduced at 1.5 years. However, in SHR segments, the greatest relaxation was observed at 1.5 years. The relaxation elicited by nifedipine in segments from WKY of 6-month and 1.5-year-old precontracted with NA was higher than that reached at 5-week- and 3-month-old. However, the relaxation induced in SHR of 6-month and 1.5-year-old was only higher than that obtained at 5-week-old. 3. Relaxations elicited by nifedipine in segments from WKY precontracted with K+ were smaller than those observed in age-matched SHR segments. 4. The endothelium positively and negatively modulates the relaxation to nifedipine in segments from SHR and WKY rats of different ages precontracted with K+, respectively. However, in segments of both strain precontracted with NA, endothelium removal did not alter the relaxations obtained at different ages. 5. These results suggest that the relaxation elicited by nifedipine: (1) depends on the strain, with a tendency to be greater in the hypertensive strain; (2) is negatively and positively modulated by endothelium in WKY and SHR, respectively, and (3) is influenced by age, and this influence depends on both the contractile agent and the strain.

Age-related changes in vascular responses: a review

Normal aging is associated with different changes in the cardiovascular system that lead to an increase in pathological processes, such as hypertension, coronary artery disease, heart failure, and postural hypotension with enhancement of both morbidity and mortality. The vascular alterations consist of changes in the function and structure of the arteries, and increasing vascular stiffness, mainly when atherosclerosis is present, whose incidence is increased with age. The arteries accumulate lipids, collagen, and minerals. Cerebral perfusion may be reduced in the elderly, mainly regional cerebral blood flow, which leads to a deterioration of mental and physical functions. The degree of deterioration is increased when aging is associated with hypertension. Aging alters endothelial cells, which play an important role in vascular tone regulation. Such a process tends to reduce endothelium-dependent relaxations, and clearly reduces the vasodilation elicited by beta-adrenoceptor agonists. The contractions induced by different agents, such as 5-hydroxytryptamine, histamine, high potassium and angiotensin are barely affected with aging, whereas those elicited by noradrenaline or endothelin are usually reduced. However, plasma noradrenaline levels are increased with age, mainly due to a reduction in the sensitivity of presynaptic alpha 2-adrenoceptors and also of noradrenaline uptake. Sodium pump activity, that controls cellular ionic homeostasis, may be altered depending on animal species. Finally, vascular Ca2+ regulation appears to be altered and the extracellular Ca2+ dependence of contractile responses elicited by agonists is increased, which justifies the enhanced sensitivity to Ca2+ antagonists in senescence.

Influence of endothelium on cultured vascular smooth muscle cell proliferation

The endothelium exerts a large influence on the underlying vascular smooth muscle, not only by the release of both contracting and relaxing factors but also by its ability to synthesize a large number of molecules that influence vascular smooth muscle growth. In addition to well-characterized growth promoters or growth inhibitors, some endothelium-derived factors, originally described as vasoactive compounds, seem to possess growth-regulatory properties. The vasoconstrictor endothelin-1 elicited a dose-dependent increase of cultured vascular smooth muscle cell DNA synthesis with a maximal effect of 57 +/- 14% over basal levels, whereas vasodilators such as prostacyclin, sodium nitroprusside, and 8-bromoguanosine 3':5'-cyclic monophosphate reduced DNA synthesis by 19 +/- 5%, 22 +/- 2%, and 31 +/- 3%, respectively. Medium conditioned by cultured bovine aortic endothelial cells markedly stimulated both DNA synthesis and proliferation of smooth muscle cells. When medium was conditioned in the presence of the endothelin-converting enzyme inhibitor phosphoramidon, the mitogenic effect was significantly reduced, thus indicating a role for endothelin in the stimulation of smooth muscle cell growth by endothelial cells. However, when both cell types were maintained in a coculture system, a 13 +/- 2% decrease of DNA synthesis was observed in smooth muscle cultures. The addition of the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester, the cyclooxygenase inhibitor indomethacin, or both during the coculture period did not revert the antiproliferative effect of endothelial cells in coculture, thereby indicating it is not likely due to these unstable endothelium-derived vasorelaxant molecules.

Intercellular signaling in neuronal-glial networks

Glial cells have recently been found to exhibit electrophysiological and metabolic responses to many neurotransmitters and neuromodulators. These findings have focused attention on the possibility that active signaling between neurons and glia could represent an important form of intercellular communication within the brain. Since glial and neuronal networks are both physically and metabolically interlinked, such intercellular signaling may represent a mechanism for inducing collective changes in the cellular physiology of neuronal and glial cell populations. Within the nervous tissue of both vertebrate and invertebrate organisms, glial cells are known to secrete extracellular signal molecules, modulate carbohydrate metabolism, and control the volume and ionic composition of extracellular space. In this paper, the roles that cytoplasmic [Ca2+] transients may play in regulating these glial cell functions are reviewed. Mechanisms by which intracellular Ca oscillations and intercellular Ca waves may be generated in neurotransmitter-stimulated glial cells are also discussed. In addition, it is proposed that rhythmic glial cell contractions and shape changes, which have been observed for many decades, are linked to Ca-induced secretion of ions, water, and neuroactive compounds. These activities represent mechanisms by which Ca-induced changes in glial cell physiology could potentially alter the excitability of neuronal networks.

Role of nitric oxide on the endothelium-dependent vasodilation in newborn piglet cerebral arteries

1. The present study was undertaken to determine whether endothelial nitric oxide (NO) is involved in the endothelium-dependent vasodilation elicited by bradykinin (BK) in rings of newborn (1-7-day-old) piglet cerebral arteries precontracted with KCl (25 mM). 2. In these rings, BK (10(-10)-10(-6) M) induced concentration-dependent relaxation. The preincubation with the precursor of NO synthesis, L-arginine (10(-4) M), reduced KCl-induced contraction and increased the BK relaxation. However, preincubation with the NO synthase inhibitor, NG-nitro-L-arginine-methyl ester (L-NAME; 3 x 10(-5) M), increased KCl contraction and basal tone, and inhibited BK relaxation. 3. These results suggest that the endothelium of these arteries possesses the ability to produce NO, either basal or stimulated by agents like BK.

Treatment with the anabolic steroid, nandrolone, reduces vasoconstrictor responses in rabbit arteries

The objective of this study was to analyze the effect of chronic treatment of rabbits for 4, 8 and 12 weeks with the anabolic steroid, nandrolone, on the contractile responses induced by different agents in segments of thoracic aorta and mesenteric and femoral arteries. In the three types of arteries, the contractions elicited by noradrenaline, 5-hydroxytryptamine and angiotensin II were increased by endothelium removal. The treatment reduced the contractions elicited by the three agents (mainly those caused by 5-hydroxytryptamine) in aorta, and only those caused by 5-hydroxytryptamine in mesenteric arteries. Ca(2+)-free medium containing 0.1 mM ethylene glycol bis (beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) reduced the responses elicited by 1 microM noradrenaline, 10 microM 5-hydroxytryptamine and 0.1 microM angiotensin II in aorta segments from control rabbits. Addition of CaCl2 to this medium restored the initial responses elicited by the three agents in normal medium, both in arteries from control and treated rabbits. In aorta, the contractions elicited by phorbol 12,13-dibutyrate (PDB), an activator of protein kinase C, were reduced by the treatment. Staurosporine, an inhibitor of protein kinase C, reduced the responses evoked by PDB. Likewise, the contractions caused by noradrenaline, 5-hydroxytryptamine and especially by angiotensin II were also reduced by staurosporine. These results suggest that the thoracic aorta is the most affected by the treatment, and that the reduction of contractile responses appears to be due to changes in protein kinase C activity and/or in a mechanism situated beyond protein kinase C activation.

Chronic treatment with the anabolic steroid, nandrolone, inhibits vasodilator responses in rabbit aorta

The effect of chronic treatment of rabbits for 4, 8 and 12 weeks with the anabolic steroid, nandrolone, on vasodilator responses was studied in segments of different arteries. The treatment abolished endothelium-dependent relaxation caused by acetylcholine and the Ca(2+)-ionophore, A23187, in thoracic aorta, and reduced endothelium-independent relaxations induced by exogenous nitric oxide (NO) or sodium nitroprusside. The inhibitor of NO synthesis, NG-monomethyl-L-arginine, abolished vasodilator responses to acetylcholine and A23187. In contrast, relaxation induced by acetylcholine, NO or sodium nitroprusside in mesenteric and femoral arteries was unaltered by nandrolone treatment. Bioassay experiments using donor segments and endothelium-denuded bioassay rings from thoracic aorta show that acetylcholine, applied either through control or treated (12 weeks) donor segments, produced similar relaxation in bioassay rings from control rabbits, but this relaxation was markedly reduced in rings from treated rabbits. The increases of cyclic GMP levels induced by acetylcholine or sodium nitroprusside in segments from thoracic aorta were abolished by nandrolone treatment. These results suggest that the treatment with nandrolone reduces NO-mediated relaxation only in thoracic aorta by inhibition of guanylate cyclase, endothelial NO production and vasodilator machinery being unaltered.

Neurogenic component of ouabain-evoked contractions is modulated by the endothelium

The influence of endothelium on the neurogenic component of ouabain-induced contractions in isolated perfused guinea pig carotid arteries was analyzed. Ouabain (0.1 mumol/L to 0.1 mmol/L) evoked concentration-dependent increases of perfusion pressure. Phentolamine (0.3 to 10 mumol/L) and prazosin (30 nmol/L to 10 mumol/L) (nonselective antagonist of alpha-adrenergic receptors and selective antagonist of alpha 1-adrenergic receptors, respectively) induced a concentration-dependent relaxation in segments precontracted with ouabain (0.1 mmol/L). When the arteries were preincubated with those blockers (both at 3 mumol/L) or the animals were pretreated with reserpine, the contractions to the glycoside were diminished, indicating that they are partially mediated by norepinephrine release from adrenergic nerve endings. De-endothelialization abolished the effect of adrenergic blockade on ouabain-induced contractions. On the other hand, de-endothelialization did not modify significantly the effect of the adrenergic blockade on norepinephrine-induced contractions. The nitric oxide blocker oxyhemoglobin, at concentrations (10 mumol/L) that abolished endothelium-dependent relaxations induced by 3 mumol/L acetylcholine; or the cyclooxygenase blocker indomethacin (10 mumol/L) did not modify the relaxation caused by phentolamine. In bioassay experiments, 30 mumol/L phentolamine induced a relaxation on the ouabain-elicited contraction only when the glycoside was added through a donor segment with endothelium. Ouabain-induced tritiated norepinephrine release was significantly reduced by the removal of endothelium but not by 1 mumol/L oxyhemoglobin or 1 mumol/L indomethacin. These results suggest that the endothelium modulates the neurogenic component involved in contractions evoked by the glycoside by a diffusible factor (or factors) whose nature is unknown; however, the factor is neither nitric oxide nor a cyclooxygenase-related compound.

Endothelium-dependent noradrenaline-induced relaxation of rat isolated cerebral arteries: pharmacological characterization of receptor subtypes involved

1. The endothelium-dependence of catecholamine-induced relaxation of rat cerebral arteries was investigated in vitro. 2. In the basilar artery (BA), the maximal relaxant response was most pronounced with noradrenaline (NA), less with isoprenaline (Iso), and only very little with terbutaline. Methoxamine and the alpha 2-adrenoceptor selective agonists BHT 933 and clonidine, had no relaxant effect. 3. In BA, the relaxation by NA or Iso was markedly attenuated by N omega-nitro-L-arginine (L-NOARG) 10(-4) M. Short term perfusion of the vessels by Triton X 100 (1:1,000) suppressed the NA-induced relaxation. 4. The relaxation induced by NA or Iso was markedly reduced in presence of L-NOARG in the posterior, medial and anterior cerebral artery. 5. In BA, NA-induced relaxation was non-competitively inhibited by propranolol, atenolol, and the beta 1- and beta 2-adrenoceptor selective antagonists, CGP 20712 A and ICI 118551. 6. The relaxant NA-effect was not affected by prazosin but was non-competitively blocked by phentolamine. 7. The Iso-induced relaxation was competitively blocked by propranolol, whereas atenolol, CGP 20712 A and ICI 118551 caused a non-competitive inhibition. 8. The experiments indicate that the catecholamine-induced relaxation in rat isolated cerebral arteries depends upon the endothelium. They suggest that the NA-induced relaxation of BA is mediated by different alpha- and beta-adrenoceptors and that the Iso-induced relaxation is mediated by different beta-receptors. The findings would also be compatible with the idea of a receptor type which cannot be characterized by the pharmacological tools that we have used.

Effects of the new anti-ulcer drug ecabet sodium (TA-2711) on pepsin activity. I. Inactivation of enzyme protein

To investigate the mechanism of the anti-peptic action of ecabet sodium (TA-2711) observed in pylorous-ligated rats, effects of this drug on the peptic activity of rat gastric juice, purified hog pepsin and pepsinogen were studied in vitro. After incubation with or without ecabet at acidic pH, the reaction mixture was centrifuged, and the peptic activity of the supernatant was measured. Ecabet depressed the peptic activity of pepsin and pepsinogen in parallel with a decrease in the protein concentration of the respective supernatant. Depression was greatest with pepsinogen (97% at 2.5 mg/ml of the drug) followed by gastric juice (about 60% at 10 mg/ml), and inhibition of the peptic activity of pepsin was weakest (about 10% at 10 mg/ml). When a fraction of the rat gastric juice containing substances with molecular weights below 10,000 was added to the pepsin solution, the anti-peptic activity of ecabet was potentiated. These results suggest that oral dosing of ecabet reduces the peptic activity of gastric juice by precipitating pepsin, which is facilitated by an unknown component(s) of gastric juice, and that the inactivation of pepsinogen may also contribute to the anti-peptic activity of ecabet.

Role of cyclic AMP in promoting the thromboresistance of human endothelial cells by enhancing thrombomodulin and decreasing tissue factor activities

1. The effects of forskolin, prostaglandin E1 (PGE1), dibutyryl cyclic AMP (db cyclic AMP), dibutyryl cyclic GMP (db cyclic GMP) and 3-isobutyl-l-methyl-xanthine (IBMX) were investigated on the expression of tissue factor and thrombomodulin activities on the surface of human saphenous vein endothelial cells (HSVEC) in culture. 2. Forskolin (10(-6) to 10(-4) M), PGE1 (10(-7) to 10(-5) M) and db cyclic AMP (10(-4) to 10(-3) M) caused a concentration-dependent decrease of cytokine-induced tissue factor activity. 3. Similar concentrations of forskolin, PGE1 and db cyclic AMP enhanced significantly constitutive thrombomodulin activity and reversed the decrease of this activity caused by interleukin-1 (IL-1). 4. IBMX (10(-4) M) decreased tissue factor activity and enhanced the effect of forskolin on tissue factor and thrombomodulin activities. 5. Forskolin (10(-4) M) decreased the IL-1-induced tissue factor mRNA and increased the thrombomodulin mRNA level. IL-1 did not change the thrombomodulin mRNA level after 2 h of incubation with HSVEC in culture. 6. Dibutyryl cyclic GMP (10(-4) M to 10(-3) M) did not influence tissue factor or thrombomodulin activity. 7. Our data suggest that elevation of intracellular cyclic AMP levels may participate in the regulation of tissue factor and thrombomodulin expression, thus contributing to promote or restore antithrombotic properties of the endothelium.

Endothelial role in ouabain-induced contractions in guinea pig carotid arteries

The influence of endothelium on the direct contractile effects of ouabain in vascular smooth muscle was analyzed in isolated perfused guinea pig carotid arteries. After blocking the neurogenic component of the glycoside contraction with alpha-adrenergic receptor blocking drugs or treating the animals with reserpine, ouabain-induced contractions were markedly reduced in vessels with intact endothelium. However, removal of the vascular endothelium from reserpinized carotid arteries resulted in ouabain-induced contractions similar to those observed in control arteries. These effects were not mimicked by the inhibitor of nitric oxide NG-monomethyl L-arginine or by the cyclooxygenase blocker indomethacin. Bioassay experiments suggested that these endothelial effects are mediated by diffusible factors. Uptake of 86Rb to measure sodium pump activity was significantly reduced by removal of the endothelium. These results suggest the existence of an inhibitory modulation by the endothelium of contractions induced by ouabain, likely mediated by a diffusible factor (or factors) released from these cells. The nature of this substance is unknown, but it is neither related to prostaglandins nor a nitric oxide-related compound. Its mechanism of action could be the stimulation of vascular sodium pump activity, the antagonism of the pump's inhibition by ouabain, or both.

Characterization of inhibitory neurotransmission in the isolated corpus cavernosum from rabbit and man

1. NG-nitro-L-arginine (L-NOARG, 10(-4) M), an inhibitor of nitric oxide (NO) synthesis, had no contractile effect on isolated preparations of rabbit and human corpus cavernosum at baseline tension, but increased tension in preparations contracted by noradrenaline (rabbit 10(-5) M, man 3 x 10(-7)-3 x 10(-6) M) or K+ (rabbit 60 mM). 2. Electrical field stimulation (supramaximal voltage, 0.8 ms pulses, 5 s train duration, 0.5-35 Hz) of rabbit and human corpus cavernosum preparations contracted by noradrenaline (rabbit 10(-5) M, man 3 x 10(-6) M) or endothelin-1 (rabbit 10(-8) M) produced relaxations that were sensitive to tetrodotoxin (10(-6) M), and dependent on the frequency and number of pulses delivered. L-NOARG (10(-6)-10(-4) M), but not NG-nitro-D-arginine (D-NOARG, 10(-6)-10(-4) M), inhibited electrically induced relaxations in a concentration-dependent manner, and at 10(-4) M the relaxations were virtually abolished. L-Arginine (10(-3) M), but not D-arginine (10(-3) M), partly reversed the inhibitory effect of L-NOARG (10(-4) M). In rabbit corpus cavernosum preparations, as with Methylene Blue (3 x 10(-5) M), an inhibitor of the soluble guanylate cyclase, and haemoglobin (10(-5) M), sequestering NO in the extracellular space, significantly reduced electrically evoked relaxations. Scopolamine (10(-6) M) had little or no effect on relaxations induced by electrical field stimulation. 3. Preparations of rabbit and human corpus cavernosum contracted by noradrenaline (rabbit 10(-5) M, man 3 x 10(-6) M) were relaxed by carbachol (10(-9)-10(-4) M) in a concentration-dependent manner. Scopolamine (10(-6) M) and L-NOARG (10(-4) M) abolished, and Methylene Blue (3 x 10(-5) M) and haemoglobin (10(-5) M) greatly reduced, the carbachol-induced relaxation, while D-NOARG (10(-4) M) had no significant effect. 4. In rabbit corpus cavernosum preparations contracted by noradrenaline (10(-5) M), L-NOARG (10(-4) M) had no significant effect on relaxations induced by vasoactive intestinal polypeptide (10(-6) M). 5. SIN-1 (3-morpholino-sydnonimin hydrochloride, 10(-8)-3 x 10(-4) M), which spontaneously liberates NO, relaxed preparations of rabbit and human corpus cavernosum contracted by noradrenaline (rabbit 10(-5) M, man 3 x 10(-6) M) or endothelin-1 (rabbit 10(-8) M, man 3 x 10(-9) M) in a concentration-dependent way.(ABSTRACT TRUNCATED AT 400 WORDS)

Nitrergic transmission: nitric oxide as a mediator of non-adrenergic, non-cholinergic neuro-effector transmission

1. The possibility that transmission at some non-adrenergic, non-cholinergic (NANC) neuro-effector junctions is mediated by nitric oxide (NO) arose from the discoveries that NO mediated the effects of nitrovasodilator drugs and that endothelium-derived relaxing factor (EDRF) was NO or a NO-yielding substance. 2. NO donated by nitrovasodilator drugs or formed by endothelial cells activates soluble guanylate cyclase in smooth muscle and the consequent increase in cyclic guanosine monophosphate (cGMP) results in relaxation. The relaxations produced by stimulation of some NANC nerves are also due to a rise in cGMP. 3. The biosynthesis of NO by oxidation of a terminal guanidino nitrogen of L-arginine is inhibited by some NG-substituted analogues of L-arginine. These substances block EDRF formation by NO synthase and endothelium-dependent vasodilatation, and the blockade is overcome by L-arginine 4. NANC relaxations in some tissues are blocked by NG-substituted analogues of L-arginine and restored by L-arginine. Other agents that affect endothelium-dependent vasodilator responses produce corresponding changes in responses to stimulation of these NANC nerves. Such observations indicate that transmission is mediated by NO: we have termed this mode of transmission nitrergic. 5. There is evidence for nitrergic innervation of smooth muscle in the gastrointestinal tract, genito-urinary system, trachea and some blood vessels (penile and cerebral arteries). 6. The recognition of a mediator role for NO in neurotransmission calls for reconsideration of previously accepted generalizations about mechanisms of transmission. 7. Studies on nitrergic transmission will provide new insights into physiological control mechanisms and pathophysiological processes and may lead to new therapeutic developments.

Vasoconstrictive responses elicited by endothelin in bovine cerebral arteries

1. Endothelin (ET-1) induced concentration-dependent contractions, which were slowly developed in segments of bovine cerebral arteries. Furthermore, this agent produced tachyphylaxis. 2. The contractions evoked by ET-1 were markedly reduced in Ca-free medium containing 1 mM EGTA and by the Ca channel antagonist, nifedipine (1 microM), but increased by the Ca channel agonist, BAY K 8644 (10 nM). 3. The contractions caused by ET-1 were significantly reduced by the protein kinase C (PKC) inhibitor, staurosporine (1 and 10 nM). 4. These results indicate that ET-1 induced potent vasoconstrictive responses, probably mediated by PKC activation, which were mainly dependent on extracellular Ca; this Ca enters the smooth muscle cells via dihydropyridine sensitive Ca channels.