Endothelial regulation of vascular tone and growth

Potential role of endothelin and nitric oxide in physiology and pathophysiology of the lower urinary tract

Endothelium-derived vasoactive mediators (endothelin-1 with its vasoconstrictive and mitogenic properties and nitric oxide with its vasodilatory and antiproliferative properties) play an important role in the regulation of vascular smooth muscle tone and cellular proliferation. Several recent studies have now demonstrated the presence of these vasoactive agents in the urinary tract where they are thought to play a prominent role in urinary tract physiology and disease. This article reviews the synthesis, localisation and actions of endothelin and nitric oxide in the lower urinary tract and examines the possible role of these mediators in disease.

Panax quinquefolium L. inhibits thrombin-induced endothelin release in vitro

Endothelial cell damage is considered to be the initial step in the genesis of thrombosis and arteriosclerosis, the common precursors of cardiovascular disorders. In this study, we evaluated the protective effects of American ginseng or Panax quinquefolium L. extracts on endothelial cell injury, and investigated effects of ginseng extracts on thrombin-induced endothelin release using cultured human umbilical vein endothelial cells. We observed that when endothelial cells pretreated with 1, 10, and 100 micrograms/ml of Panax quinquefolium L. extracts were incubated for 4 and 24 hr with thrombin, the concentration of endothelin was significantly decreased in a concentration dependent, time related manner (at 4 hr, IC50 = 5.1 micrograms/ml; at 24 hr, IC50 = 6.2 micrograms/ml). We further evaluated the effects of NG-nitro-L-arginine (NLA), a nitric oxide (NO) synthetase inhibitor, on the activity of Panax quinquefolium L. extracts. Following pretreatment of cultured endothelial cells with NLA, the inhibition of thrombin-induced endothelin release by Panax quinquefolium L. was significantly reduced (P < 0.05). This result suggests that the pharmacological action of Panax quinquefolium L. is, at least partially, due to NO release. Our data demonstrate that American ginseng may play a therapeutic role in facilitating the hemodynamic balance of vascular endothelial cells.

Effects of quercetin on the release of endothelin, prostacyclin and tissue plasminogen activator from human endothelial cells in culture

Quercetin and related flavonoids are naturally occurring polyphenolic compounds with multiple pharmacological activities. Using cultured human umbilical vein endothelial cells, we investigated the effects of quercetin on endothelin (ET-1) and tissue plasminogen activator (t-PA) release induced by thrombin. We observed that when endothelial cells pretreated with 5 or 50 microM of quercetin were incubated for 4 and 24 h with thrombin, ET-1 concentration-dependently decreased (n = 6, P < 0.01, at 4 h IC50 = 1.54 microM, at 24 h IC50 = 2.78 microM). Under the same experimental conditions, quercetin significantly increased t-PA (n = 6, P < 0.01, at 4 h EC50 = 0.71 microM and at 24 hrs EC50 = 0.74 microM). In the same preparation, we evaluated prostacyclin (PGI2) release, induced by thrombin activated platelets, as determined by a 6-Keto-PGF1alpha radioimmunoassay. Following the treatment of cultured endothelial cells with activated platelets, the concentration of 6-Keto-PGF1alpha was significantly increased (P < 0.01). Quercetin (1, 5, and 20 microM) inhibited PGI2, in a concentration-dependent manner (n = 6, P < 0.05). Our data indicate that quercetin modulates the release of ET-1, t-PA, and PGI2 from vascular endothelial cells.

Effects of age, gender and metabolic factors on endothelium-dependent vasodilation: a population-based study

OBJECTIVES

A progressive decline in endothelium-dependent vasodilation (EDV) in the human forearm with age has previously been reported. The aim of this study was to evaluate the interplay between age, gender and metabolic factors on EDV in healthy subjects in a population-based study.

SETTING

Tertiary university hospital.

SUBJECTS AND DESIGN

Thirty-six healthy men and 30 women, aged 20-69 years, underwent measurements of forearm blood flow (FBF) at rest and during local infusions of 2 and 4 microg min-1 of metacholine (evaluating EDV) and 5 and 10 microg min-1 of sodium nitroprusside (evaluating endothelium-independent vasodilation, EIDV) and during reactive hyperaemia by venous occlusion plethysmography.

RESULTS

Age was inversely related to EDV (r = - 0.41, P < 0.05 in men; r = - 0.61, P < 0.01 in women) and maximal FBF during reactive hyperaemia in both men and women. EIDV was significantly related to age in an inverse way in women only. EDV was more pronounced in females than in males before menopause (48 +/- 3 SD years, 635 +/- 186 vs. 502 +/- 269% in males, P < 0.05), but similar in women and men thereafter (374 +/- 141 vs. 370 +/- 185% in men). The slope of the regression line for the relationship between age and EDV was flatter in premenopausal than in postmenopausal women (- 2.3 vs. - 6.4), whilst this slope was similar in younger and older men (- 5.5 vs. - 5.3). In multiple regression analysis, fasting blood glucose levels and the waist/hip ratio remained the only significant predictors of EDV in men (P < 0.01 for both), whilst age was the only significant independent predictor of EDV in women (P < 0.01).

CONCLUSION

The interplay between age and metabolic factors as determinants of endothelial function is different in healthy men and women.

Ursodeoxycholic acid and endothelial-dependent, nitric oxide-independent vasodilatation of forearm resistance arteries in patients with coronary heart disease

AIMS

Ursodeoxycholic acid (UDCA) has cholesterol lowering and anti-inflammatory effects and bile acids are reported to exert vasodilator effects; all of these properties might be considered desirable in a drug used in the treatment of patients with coronary heart disease. We investigated a hypothesis that UDCA may dilate arteries and the mechanism of action.

METHODS

We evaluated effects of a 6-week treatment with UDCA in 11 coronary heart disease patients on endothelium-dependent (acetylcholine-induced) and -independent (nitroprusside-induced) vasodilatations in forearm vasculature by strain-gauge plethysmography. Healthy individuals (n=14) served as baseline controls.

RESULTS

The percentage increase by acetylcholine in the flow of the infused arm relative to the non-infused arm of coronary heart disease patients during the trial remained unaltered, but vasodilatation to NG-monomethyl-l-arginine+acetylcholine was improved by 161+/-27% with UDCA vs 83+/-22% with placebo (mean difference 91% [95% CI 35%, 147%], P=0.016).

CONCLUSIONS

Six weeks' UDCA therapy improved endothelium-dependent nitric oxide-independent vasodilatation, which might maintain arterial flow in coronary heart disease patients under conditions of impaired nitric oxide production.

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.

Combination of ACE inhibitors and calcium antagonists: a logical approach

An increasing body of evidence indicates that impairment of endothelial function is crucially involved in the pathogenesis of cardiovascular disease. Injury to the endothelium precipitates atherosclerosis by causing smooth-muscle cell migration and proliferation, induction of expression of growth factors, and impairment of plasma coagulation and endogenous fibrinolysis. Angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists are widely used in patients with cardiovascular disease and have beneficial vascular effects beyond blood pressure control alone. Both exhibit a synergistic hemodynamic profile. Whereas calcium antagonists dilate large conduit and resistance arteries, ACE inhibitors inhibit the renin-angiotensin system (RAS) and reduce sympathetic outflow. Certain calcium antagonists, such as verapamil and diltiazem, reduce heart rate, whereas dihydropyridines tend to increase it. In the blood vessel wall, the local vascular effects of ACE inhibitors and calcium antagonists are complementary. ACE inhibitors diminish transformation of angiotensin I (Ang I) into angiotensin II (Ang II) and prevent degradation of bradykinin [which stimulates nitric oxide (NO) and prostacyclin formation]. Calcium antagonists inhibit the effects of Ang I and endothelin-1 (ET-1) at the level of vascular smooth muscle by reducing Ca2+ inflow and facilitating the vasodilator effects of NO. The resistance circulation is particularly dependent on extracellular Ca2+, thereby explaining why nifedipine and verapamil effectively inhibit ET-induced vasoconstriction in vitro and in vivo. In hypertension, ACE inhibitors and calcium antagonists markedly improve structural changes and increase the media/lumen ratio in resistance arteries. Long-term combination therapy with verapamil and trandolapril is particularly effective in reversing endothelial dysfunction in hypertensive animals. ACE inhibitors substantially reduce morbidity and mortality in patients with left ventricular dysfunction after myocardial infarction (MI). There is a strong trend indicating benefit with verapamil as well, but this is confined to patients with a normal left ventricular ejection fraction. Clinical studies have confirmed that calcium antagonists exhibit antiatherogenic properties. However, the clinical relevance of these findings has recently been disputed because short-acting dihydropyridines are reported to increase risk for MI. Because ACE inhibitors and calcium antagonists exhibit synergistic hemodynamic, antiproliferative, antithrombotic, and antiatherogenic properties, combination therapy provides a promising concept in patients with cardiovascular and renal disease.

Endothelin-stimulated nitric oxide production in the isolated Kupffer cell

Endothelin (ET) is a potent peptide mediator exhibiting a wide variety of effects in both the parenchymal and nonparenchymal hepatic cells. In the Kupffer cell, ET activates several transmembrane signaling pathways to generate numerous second messengers including the phospholipase C-generated products inositol-1,4,5-trisphosphate and diacylglycerol and the cyclooxygenase product prostaglandin E2 via specific ETB-type receptors. In addition to these findings, we have now demonstrated that endothelin stimulates the production of nitric oxide (NO) in the Kupffer cell in a time- and concentration-dependent manner. Western blot analysis indicates that ET-stimulated NO production occurs though activation of the inducible form of the nitric oxide synthase enzyme. These findings have important implications as the stimulation of NO production by ET may be part of the physiological response to inflammation or infection. Elevated levels of ET and NO have been found to be associated with numerous hepatic pathophysiological conditions that may contribute to derangements in the vascular system seen in these conditions.

Vascular effects of cyclosporin A and acute rejection in canine heart transplantation

BACKGROUND

Alteration of coronary vascular regulation during acute rejection may induce graft dysfunction and promote the occurrence of coronary atherosclerosis in transplant recipients. We studied the effects of treated and untreated acute rejection on coronary vascular regulation.

METHODS

Two groups of mongrel dogs (n = 7) underwent heterotopic heart transplantation (cervical position) and received either no treatment (group 1) or cyclosporin A (CyA), 10 mg.kg-1.day-1 (group 2). On day 7, recipient native and transplanted hearts were harvested and studied in organ chambers for coronary vascular reactivity.

RESULTS

Transplanted hearts from group 1 displayed grade IV histologic rejection, whereas those from group 2 displayed grade IIIA to IV rejection. Intimal hyperplasia was found in the coronary arteries of both groups. Immunoperoxidase staining revealed the presence of factor VIII and of immunoglobulin M and G antibodies on the endothelium of both groups. Coronary relaxation to thrombin was impaired in transplanted hearts compared with native hearts (p < 0.05), and this was not influenced by CyA treatment. Conversely, endothelium-dependent relaxation to 5-hydroxytryptamine was enhanced in both CyA-treated (p < 0.01) and untreated groups (p < 0.05). A facilitating effect of CyA on 5-hydroxytryptamine also was seen in transplanted hearts in group 1 versus group 2 (p < 0.05), suggesting an intrinsic effect of CyA. Endothelium-independent relaxation to sodium nitroprusside and the contractile response to prostaglandin F2 alpha were not affected.

CONCLUSIONS

In our model, acute rejection did not specifically impair cyclic guanosine monophosphate-mediated relaxation, but it did affect, in a receptor-specific manner, endothelium-dependent relaxation. Cyclosporin A appeared to enhance coronary endothelial sensitivity to 5-hydroxytryptamine.

The kidney in blood pressure regulation and development of hypertension

Systemic arterial pressure is a dynamic and responsive physiologic parameter that can be influenced by many different factors. In particular, short-term changes in arterial pressure are caused by a myriad of mechanisms that affect cardiac output, total peripheral resistance, and cardiovascular capacitance. In the long run, however, most of these actions can be buffered or compensated by appropriate renal adjustments of sodium balance, ECFV, and blood volume. As long as the mechanisms regulating sodium excretion can maintain sodium balance by appropriately modulating the sensitivity of the pressure-natriuresis relationship, normal arterial pressure can be sustained. Derangements that compromise the ability of the kidneys to maintain sodium balance, however, can result in the kidney's need for an elevated arterial pressure to reestablish net salt and water balance.

Cyclooxygenases and the central nervous system

Prostaglandins (PGs) were first described in the brain by Samuelsson over 30 years ago (Samuelsson, 1964). Since then a large number of studies have shown that PGs are formed in regions of the brain and spinal cord in response to a variety of stimuli. The recent identification of two forms of cyclooxygenase (COX; Kujubu et al., 1991; Xie et al., 1991; Smith and DeWitt, 1996), both of which are expressed in the brain, along with superior tools for mapping COX distribution, has spurred a resurgence of interest in the role of PGs in the central nervous system (CNS). In this review we will describe new data in this area, focusing on the distribution and potential role of the COX isoforms in brain function and disease.

Is there a rationale for combining angiotensin-converting enzyme inhibitors and calcium antagonists in cardiovascular disease?

Coronary artery disease and its sequelae remain the most important cause of morbidity and mortality in Western countries. Because the pathophysiologic characteristics of coronary artery disease are multifactorial, impairment of endothelial function featuring enhanced vasoconstriction, increased platelet vessel wall interaction, adherence of monocytes, migration and proliferation of vascular smooth muscle cells are crucially involved. Endothelial cells release numerous vasoactive substances regulating function of vascular smooth muscle and trafficking blood cells such as nitric oxide (NO), which is a potent vasodilator also inhibiting cellular growth and migration. In addition, NO possesses antiatherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. These effects are counterbalanced by endothelial vasoconstrictors such as angiotensin II and endothelin-1. In the blood vessel wall, the local vascular effects of angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists are synergistic. ACE inhibitors diminish the conversion of angiotensin I into angiotensin II and the inactivation of bradykinin. Calcium antagonists counteract angiotensin II and endothelin-1 at the level of vascular smooth muscle by reducing Ca2+ inflow and facilitating the vasodilator effects of NO. In hypertensive animals, long-term combination therapy with verapamil and trandolapril is particularly effective in reversing endothelial dysfunction. Further, ACE inhibitors and calcium antagonists exert beneficial vascular and complementary hemodynamic effects. Whereas ACE inhibitors inhibit the renin-angiotensin system and reduce sympathetic outflow, calcium antagonists dilate large conduit and resistance arteries. Because small vessels appear to be more dependent on extracellular Ca2+ than larger vessels, nifedipine and verapamil effectively inhibit endothelin-induced vasoconstriction in vitro and in vivo in the resistance circulation. Long-term treatment with ACE inhibitors substantially reduces morbidity and mortality rates in patients with left ventricular dysfunction after myocardial infarction; beneficial effects of verapamil in secondary prevention are confined to patients with normal left ventricular ejection fraction. In summary, long-term combination therapy of ACE inhibitors and calcium antagonists might provide beneficial effects in cardiovascular disease because they exert synergistic hemodynamic, antiproliferative, antithrombotic, and antiatherogenic properties.

Single LDL apheresis improves endothelium-dependent vasodilatation in hypercholesterolemic humans

BACKGROUND

Although long-term lipid-lowering therapy improves endothelium-dependent vasodilatation in humans, it remains unknown whether the short-term removal of LDL per se ameliorates endothelial dysfunction.

METHODS AND RESULTS

To examine the effects of a single session of LDL apheresis on endothelial function in patients with hypercholesterolemia, we measured forearm blood flow (FBF) by strain-gauge plethysmography before and after single LDL apheresis while infusing acetylcholine (ACh; 4 to 24 micrograms/min) and sodium nitroprusside (SNP; 0.2 to 1.2 micrograms/min). The single session of LDL apheresis reduced total LDL (from 142.2 +/- 15.0 to 32.6 +/- 5.0 mg/mL, P < .0005) and oxidized LDL (from 111.6 +/- 22.8 to 30.0 +/- 5.4 ng/mL, P < .005). Although ACh and SNP increased FBF dose-dependently before and after LDL apheresis, the endothelium-dependent vasodilatation responses to ACh were significantly augmented (P < .01) after the single session of LDL apheresis without changes in the endothelium-independent vasodilatation responses to SNP. The plasma levels of total and oxidized LDL correlated with the degree of ACh-induced vasodilatation. Furthermore, the local production of nitrate/nitrite, metabolites of NO, during ACh infusion was significantly (P < .05) augmented by LDL apheresis, and there was a significant correlation between the degree of ACh-induced vasodilatation and the production in nitrate/nitrite (r = .99, P < .0005).

CONCLUSIONS

We demonstrated that even a single session of LDL apheresis with the reduction of total LDL and oxidized LDL improved endothelial function. Our results suggest that total LDL and/or oxidized LDL may directly impair endothelial function in the human forearm vessel.

The relaxation responses to corticotropin-releasing factor in rat aorta are endothelium dependent and gestationally regulated

OBJECTIVE

Our purpose was to examine the hypothesis that the relaxant response to corticotropin-releasing factor is endothelium dependent and changes during pregnancy.

STUDY DESIGN

Relaxant responses to cumulative concentrations of corticotropin-releasing hormone were measured in rings of thoracic aorta, precontracted with phenylephrine, from pregnant and nonpregnant female rats. Each group consisted of 5 to 10 rats.

RESULTS

The relaxation induced by corticotropin-releasing factor in aortic rings from nonpregnant rats decreased after deendothelization and treatment with N omega-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor), LY-83,583 (a guanylate cyclase inhibitor), or alpha-helical corticotropin-releasing factor 9-41 (a corticotropin-releasing factor antagonist). The percent decrease in relaxation at 1 nmol/L of corticotropin-releasing factor was about 88% with deendothelization, 100% with N omega-nitro-L-arginine methyl ester, 76% with LY-83,583, and 100% with alpha-helical corticotropin-releasing factor 9-41. The responses to corticotropin-releasing factor in intact rings from rats in early pregnancy were not significantly different from those in the nonpregnant female rats, but the responses were decreased during the later stages of gestation (percent decrease in relaxation at 1 nmol/L of corticotropin-releasing factor about 71% at day 20 and 98% at term). The relaxation induced by corticotropin-releasing factor during pregnancy was also inhibited by deendothelization, N omega-nitro-L-arginine methyl ester, or LY-83,583.

CONCLUSIONS

The relaxant response to corticotropin-releasing factor in the rat aorta is endothelium dependent and is mediated by the nitric oxide-cyclic guanosine monophosphate pathway. The receptor involved in this effect is alpha-helical corticotropin-releasing factor 9-41 sensitive. This inhibitory response is unchanged during early pregnancy but reduced toward the end of gestation.

Plasma endothelin-1 concentrations during cold exposure in essential acrocyanosis

To assess endothelin-1 (ET-1) response to cold stimulation in essential acrocyanosis (EA), the authors measured ET-1 plasma concentrations in 6 patients with EA (6 women, age range seventeen to thirty-seven years) and in 6 controls (5 women, 1 man, age range twenty-one to thirty-seven years) before and after cold challenge by unilateral hand immersion in water bath at 13 degrees C for five minutes. The contralateral upper limb was considered as control. Blood samples were simultaneously drawn from an antecubital vein in the cooled side and in the contralateral upper limb at baseline, at the end of cooling, and at ten and ninety minutes after cooling was begun. Plasma ET-1 was determined by a radioimmunoassay system. Results are mean +/- SD. Baseline ET-1 was higher in patients with EA (5.1 +/- 0.3 pmol/L) than in controls (1.9 +/- 0.1 pmol/L, P < 0.001). After hand cooling, ET-1 in the cold-exposed upper limb rose in patients with EA to a peak value of 7.2 +/- 0.7 pmol/L, which was greater than that observed in healthy subjects (2.7 +/- 0.4 pmol/L, P < 0.001). The absolute increase in ET-1 plasma concentrations from baseline to peak value was significantly higher in patients with EA than in controls (2.1 +/- 0.3 vs 0.8 +/- 0.2 pmol/L, respectively, P < 0.001). In patients with EA, but not in controls, the rise in ET-1 plasma concentrations was still detected ninety minutes after cooling. The same time course of the plasma ET-1 concentrations was observed in the noncooled upper limb, but the increases in ET-1 at different times after cold stimulus were smaller than in the cold-challenged upper limb in both groups (P < 0.001). In conclusion, the results demonstrate that in patients with EA, baseline plasma levels of ET-1 are enhanced and are further increased by cooling until ninety minutes after cold challenge. This rise in plasma ET-1 could contribute to potentiating and prolonging cold-induced vasoconstriction/vasospasm and/or could be a marker for endothelial damage in EA.

Regulation of endothelial nitric-oxide synthase during hypoxia

The mechanism by which nitric-oxide (NO) production increases during hypoxia is unknown. To explore the effect of hypoxia upon endothelial nitric-oxide synthase (ecNOS) activity and expression, we exposed bovine aortic endothelial cells (BAEC) to hypoxia (1% O2) for 0-24 h and measured levels of ecNOS mRNA, protein, and activity. The amount of ecNOS mRNA increases to more than twice the basal level after 6 h of hypoxia. Incubation of BAEC with actinomycin D during hypoxia prevents this increase, demonstrating that higher levels of mRNA observed during hypoxia are due to increased synthesis, not to increased stability of ecNOS mRNA. Levels of ecNOS protein increase throughout 24 h of hypoxia to more than twice normoxic levels. Although ecNOS expression increases within 2 h of hypoxia, total activity remains unchanged. To explore the transcriptional regulation of ecNOS, we constructed a reporter plasmid containing the ecNOS promoter region upstream of the luc gene and transfected this reporter plasmid into BAEC. In this system, hypoxia induces a linear increase over time in the expression of luciferase driven by the ecNOS promoter. It is concluded that hypoxia induces an increase in transcription of ecNOS in endothelial cells, activating the regulatory region of ecNOS by undefined transcription factors.

Acute effects of ethanol on responses of cerebral arterioles

BACKGROUND AND PURPOSE

Previous studies have suggested that acute exposure of large peripheral arteries to ethanol impairs endothelium-dependent relaxation. The goal of the present study was to determine the acute effects of ethanol exposure on responses of cerebral resistance arterioles in vivo.

METHODS

We prepared a cranial window in rats to expose the cerebral (pial) microcirculation. We measured the diameter of pial arterioles in vivo in response to agonists that presumably stimulate the synthesis/release of nitric oxide from the endothelium (ADP, acetylcholine, and histamine) or neurons (N-methyl-D-aspartate [NMDA]) before and after topical application of various concentrations of ethanol added to the cerebrospinal fluid (20, 40, 60, 80, and 100 mmol/L). In addition, we examined responses of pial arterioles to nitroglycerin before and 1 hour after topical application of ethanol.

RESULTS

Before application of ethanol, ADP, acetylcholine, histamine, NMDA, and nitroglycerin produced dose-related dilatation of pial arterioles. Application of the various concentrations of ethanol did not alter the baseline diameter of pial arterioles. However, application of 80 and 100 mmol/L ethanol inhibited dilatation of pial arterioles in response to agonists that stimulate the synthesis/release of nitric oxide. Dilatation of pial arterioles in response to nitroglycerin was not altered by application of ethanol.

CONCLUSIONS

The findings of the present study suggest that acute exposure of cerebral arterioles to modest-to-moderate concentrations of ethanol (20 to 60 mmol/L) does not alter responses of cerebral arterioles. In contrast, exposure of cerebral arterioles to higher concentrations of ethanol (80 and 100 mmol/L) can produce specific impairment of dilatation to agonists that stimulate the synthesis/release of nitric oxide from endothelium and neurons.

Structure and function of the rat basilar artery during chronic nitric oxide synthase inhibition

BACKGROUND AND PURPOSE

Nitric oxide is an important regulator of vascular tone and may also be implicated in the modulation of vascular growth and structure. This study presents the effects of chronic nitric oxide inhibition, with or without antihypertensive treatment, on the structure and function of the basilar artery in rats.

METHODS

Rats were treated for 6 weeks with N omega-nitro-L-arginine methyl ester (50 mg/kg per day) alone or in combination with verapamil (100 mg/kg per day) or with trandolapril (1 mg/kg per day). Untreated rats served as controls. The structure and reactivity of perfused and pressurized basilar arteries were analyzed in vitro using a video dimension analyzer.

RESULTS

Systolic arterial pressure increased only in the nitro-arginine-treated group, as did the media-to-lumen ratio of the basilar artery. This structural alteration, which was prevented by verapamil and trandolapril, was mainly due to remodeling and not to growth. Chronic inhibition of the L-arginine pathway increased the response of the basilar artery to serotonin, while the opposite was found for endothelin. Verapamil and trandolapril prevented these functional alterations that seemed related to the changes in the vascular structure.

CONCLUSIONS

The remodeling and functional alterations of the basilar artery seem to depend mainly on the elevation of arterial pressure with little contribution of the L-arginine pathway. Furthermore, nitric oxide does not seem to be implicated in the modulation of normal cerebral vascular growth in vivo. However, hypertension-induced changes in vascular reactivity and structure could alter cerebral blood flow and eventually contribute to the development of stroke in this model of hypertension.

Flow-mediated endothelial mechanotransduction

Mechanical forces associated with blood flow play important roles in the acute control of vascular tone, the regulation of arterial structure and remodeling, and the localization of atherosclerotic lesions. Major regulation of the blood vessel responses occurs by the action of hemodynamic shear stresses on the endothelium. The transmission of hemodynamic forces throughout the endothelium and the mechanotransduction mechanisms that lead to biophysical, biochemical, and gene regulatory responses of endothelial cells to hemodynamic shear stresses are reviewed.

Vascular actions of insulin in health and disease

Insulin has well known metabolic effects. However, depending on the magnitude and duration of the insulin stimulus, this hormone can also produce vasodilation and vascular smooth muscle growth. The association of hyperinsulinemia with the metabolic disorders of obesity and non-insulin-dependent diabetes, as well as with the cardiovascular pathologies of hypertension and atherosclerosis, has led to suggestions that perhaps elevated insulin levels are causally related to these diseases. Alternatively, insulin resistance may develop following an increase in skeletal muscle vascular resistance, with or without hypertension, such that a reduction in skeletal muscle blood flow leads to an attenuated glucose delivery and uptake. These hypotheses are explored in this review by examining the effects of insulin on vascular smooth muscle tissue during both acute and prolonged exposure. An interaction among hyperinsulinemia, hyperglycemia, and hyperlipidemia associated with the insulin resistant state is described whereby insulin resistance can be both a cause and a result of elevated vascular resistance. The association between blood flow and insulin stimulated glucose uptake suggests that therapeutic intervention against the development of skeletal muscle vascular resistance should occur early in individuals generally predisposed to cardiovascular pathology in order to attenuate, or avoid, insulin resistance and its sequelae.

Reduced contractile function after balloon denudation of rat carotid arteries

In rat carotid arteries isolated 2 weeks after balloon denudation, a significant neointima developed with little change in medial size. Associated with this neointimal hyperplasia was a marked decrease in contraction to various agents including angiotensins I and II, big endothelin-1, endothelin-1, norepinephrine, phenylephrine, and serotonin. Vasodilator responses to acetylcholine were significantly reduced. In contrast, vasodilator responses to nitroglycerin were unaffected. It is suggested that modulation of the neointimal cells to a more non-contractile phenotype may be responsible for the loss in contractile ability.