Carmine Cardillo

Role of endothelin in the increased vascular tone of patients with essential hypertension

We investigated the possible role of endothelin in the increased vasoconstrictor tone of hypertensive patients using antagonists of endothelin receptors. Forearm blood flow (FBF) responses (strain-gauge plethysmography) to intraarterial infusion of blockers of endothelin-A (ETA) (BQ-123) and endothelin-B (ETB) (BQ-788) receptors, separately and in combination, were measured in hypertensive patients and normotensive control subjects. In healthy subjects, BQ-123 alone or in combination with BQ-788 did not significantly modify FBF (P=0.78 and P=0.63, respectively). In hypertensive patients, in contrast, BQ-123 increased FBF by 33+/-7% (P<0.001 versus baseline), and the combination of BQ-123 and BQ-788 resulted in a greater vasodilator response (63+/-12%; P=0.006 versus BQ-123 alone in the same subjects). BQ-788 produced a divergent vasoactive effect in the two groups, with a decrease of FBF (17+/-5%; P=0.004 versus baseline) in control subjects and transient vasodilation (15+/-7% after 20 minutes) in hypertensive patients (P<0.001, hypertensives versus controls). The vasoconstrictor response to endothelin-1 was slightly higher (P=0.04) in hypertensive patients (46+/-4%) than in control subjects (32+/-4%). Our data indicate that patients with essential hypertension have increased vascular endothelin activity, which may be of pathophysiological relevance to their increased vascular tone. In these patients, nonselective ETA and ETB blockade seems to produce a greater vasodilator effect than selective ETA blockade.

Insulin Stimulates Both Endothelin and Nitric Oxide Activity in the Human Forearm

BACKGROUNDnThe mechanism of the hemodynamic effect of insulin in the skeletal muscle circulation has not been fully elucidated. The purpose of this study was to assess whether the hemodynamic response to insulin involves the concurrent release of endothelin (ET-1) and nitric oxide (NO), 2 substances with opposing vasoactive properties.nnnMETHODS AND RESULTSnBioactivity of ET-1 and NO was assessed without insulin and during insulin infusion in the forearm circulation of healthy subjects by use of blockers of ET-1 receptors and by NO synthesis inhibition. In the absence of hyperinsulinemia, ET-1 receptor blockade did not result in any significant change in forearm blood flow from baseline (P=0.29). Intra-arterial insulin administration did not significantly modify forearm blood flow (P=0. 88). However, in the presence of hyperinsulinemia, ET-1 receptor antagonism was associated with a significant vasodilator response (P<0.001). In the presence of ET-1 receptor blockade, the vasoconstrictor response to NO inhibition by N(G)-monomethyl-L-arginine was significantly higher after insulin infusion than in the absence of hyperinsulinemia (P=0.006).nnnCONCLUSIONSnThese findings suggest that in the skeletal muscle circulation, insulin stimulates both ET-1 and NO activity. An imbalance between the release of these 2 substances may be involved in the pathophysiology of hypertension and atherosclerosis in insulin-resistant states associated with endothelial dysfunction.

Vascular Effects of Estrogen and Cholesterol-Lowering Therapies in Hypercholesterolemic Postmenopausal Women

BACKGROUNDnLipoproteins affect endothelium-dependent vasomotor responsiveness. Because lipoprotein effects of estrogen and cholesterol-lowering therapies differ, we studied the vascular responses to these therapies in hypercholesterolemic postmenopausal women.nnnMETHODS AND RESULTSnWe randomly assigned 28 women to conjugated equine estrogen (CE) 0.625 mg, simvastatin 10 mg, and their combination daily for 6 weeks. Compared with respective baseline values, simvastatin alone and combined with CE reduced LDL cholesterol to a greater extent than CE alone (both P<0.05). CE alone and combined with simvastatin raised HDL cholesterol and lowered lipoprotein(a) to a greater extent than simvastatin alone (all P<0.05). Flow-mediated dilation of the brachial artery (by ultrasonography) improved (all P<0.001 versus baseline values) on CE (4.0+/-2.6% to 10.2+/-3.9%), simvastatin (4.3+/-2.4% to 10.0+/-3.9%), and CE combined with simvastatin (4.6+/-2.0% to 9.8+/-2.6%), but similarly among therapies (P=0.507 by ANOVA). None of the therapies improved the dilator response to nitroglycerin (all P>/=0.184). Only therapies including CE lowered levels of plasminogen activator inhibitor type 1 and the cell adhesion molecule E-selectin (all P<0. 05 versus simvastatin).nnnCONCLUSIONSnAlthough estrogen and statin therapies have differing effects on lipoprotein levels, specific improvement in endothelium-dependent vasodilator responsiveness is similar. However, only therapies including estrogen improved markers of fibrinolysis and vascular inflammation. Thus, estrogen therapy appears to have unique properties that may benefit the vasculature of hypercholesterolemic postmenopausal women, even if they are already on cholesterol-lowering therapy.

Xanthine Oxidase Inhibition With Oxypurinol Improves Endothelial Vasodilator Function in Hypercholesterolemic but Not in Hypertensive Patients

Hypercholesterolemic and hypertensive patients have impaired endothelium-dependent vasorelaxation because of decreased nitric oxide activity, but the mechanism underlying this abnormality is unknown. This study sought to determine whether an increased breakdown of nitric oxide by xanthine oxidase-generated superoxide anions could participate in these forms of endothelial dysfunction. We studied vascular responses to intrabrachial infusion of acetylcholine (an endothelium-dependent vasodilator, 7.5 to 30 microg/min) and sodium nitroprusside (a direct smooth muscle dilator, 0.8 to 3.2 microg/min) by strain-gauge plethysmography before and during the combined administration of oxypurinol (300 microg/min), a xanthine oxidase inhibitor, in 20 hypercholesterolemic patients, 20 essential hypertensive patients, and 20 normal subjects. The vasodilator response to acetylcholine was blunted in hypercholesterolemic (highest flow, 8.2+/-8 mL x min(-1) x dL(-1)) and hypertensive (8.5+/-4 mL x min(-1) x dL(-1)) patients compared with control subjects (13.8+/- 6.6 mL x min(-1) x dL(-1)) (both P<.001); however, no differences were observed in the response to sodium nitroprusside. Oxypurinol did not change the response to acetylcholine in control subjects (P=.26) and improved, but did not normalize, its vasodilator effect in hypercholesterolemic patients (P<.01). Oxypurinol did not affect the response to acetylcholine in hypertensive patients (P=.34) and did not modify the response to sodium nitroprusside in any group. These results suggest that xanthine oxidase-generated superoxide anions are partly responsible for the impaired endothelial vasodilator function of hypercholesterolemic patients. In contrast, this mechanism does not appear to play a significant role in essential hypertension.

Selective Defect in Nitric Oxide Synthesis May Explain the Impaired Endothelium-Dependent Vasodilation in Patients With Essential Hypertension

BACKGROUNDnPatients with essential hypertension have impaired endothelial NO activity, but the mechanism underlying this abnormality is unknown.nnnMETHODS AND RESULTSnTo investigate whether the endothelial dysfunction of hypertensive patients is related to a selective defect in NO synthesis, we studied the forearm blood flow responses to intra-arterial infusion of acetylcholine (7.5 to 30 microg/min), an endothelial agonist linked to NO synthase through the Ca2+ signaling pathway, and isoproterenol (50 to 200 ng/min), a beta-adrenoceptor agonist that stimulates NO production by increasing intracellular cAMP, in 12 normotensive subjects and 12 hypertensive patients. The infusion of isoproterenol was repeated during the concurrent blockade of NO synthesis by NG-monomethyl-L-arginine (L-NMMA; 4 micromol/min). The vasodilator response to acetylcholine was significantly reduced in hypertensives compared with normotensives (maximum blood flow: 10.4+/-4.6 versus 14.4+/-3.7 mL x min[-1] x dL[-1]; P=.008). However, the vasodilator effect of isoproterenol was similar in normotensives and hypertensives (maximum blood flow: 14.4+/-5.4 versus 13.5+/-5 mL x min[-1] x dL[-1]; P=.56) and was significantly (both P<.01) and equally blunted by L-NMMA in both groups (maximum blood flow: 11+/-3 mL x min[-1] x dL[-1] in normotensives versus 10.8+/-3.9 mL x min[-1] x dL[-1] in hypertensives; P=.77). The vasodilator response to sodium nitroprusside (0.8 to 3.2 microg/min), an exogenous NO donor, was similar in both groups and was not modified by L-NMMA.nnnCONCLUSIONSnHypertensive patients have impaired endothelium-dependent vasodilation in response to acetylcholine but preserved NO activity in response to beta-adrenergic stimulation. These findings suggest that the endothelial dysfunction in essential hypertension is due to a selective abnormality of NO synthesis, probably related to a defect in the phosphatidylinositol/Ca2+ signaling pathway.

Racial Differences in Nitric Oxide–Mediated Vasodilator Response to Mental Stress in the Forearm Circulation

An abnormal hemodynamic response to stressful stimuli has been proposed as a mechanism involved in the higher prevalence of hypertension in blacks. Given the important role of nitric oxide (NO) in the regulation of cardiovascular homeostasis, we investigated the possibility of racial differences in vascular NO activity during mental stress. To test this hypothesis, we compared the forearm blood flow (FBF) response to mental stress in 14 white and 12 black healthy subjects during intra-arterial infusion of either saline or NO synthesis inhibitor N(G)-monomethyl-L-arginine (L-NMMA; 4 micromol/min). We also examined vascular responses of the two groups to intra-arterial infusion of sodium nitroprusside (0.8 to 3.2 microg/min), an exogenous NO donor. During saline infusion, the increase in FBF from baseline induced by mental stress was significantly higher in whites than in blacks (109+/-20% versus 58+/-8%; P=0.03). L-NMMA significantly reduced stress-induced increase in FBF in whites (from 109+/-20% to 54+/-11%; P=0.004) but not in blacks (from 58+/-8% to 42+/-10%; P=0.24); thus, the vasodilator effect of stress testing during L-NMMA was similar in whites and blacks (54+/-11% versus 42+/-10%; P=0.44). The vasodilator response to sodium nitroprusside was also lower in blacks than in whites (maximum flow, 6.9+/-2 versus 11.6+/-3.5 mL x min(-1) x dL(-1); P=0.001) and was not significantly modified by L-NMMA in either group. Our findings indicate that blacks have a reduced NO-dependent vasodilator activity during mental stress. This difference seems related to reduced sensitivity of smooth muscle to the vasodilator effect of NO and may play some role in the increased prevalence of hypertension and its complications in blacks.

Reduced endothelium-dependent and -independent dilation of conductance arteries in African Americans.

OBJECTIVESnThe goal of this study was to determine whether racial differences exist in the functional behavior of conduit vessels.nnnBACKGROUNDnCompared with Caucasians, African Americans have a higher prevalence of cardiovascular disease and its complications, which may be related to reduced nitric oxide (NO)-dependent and -independent vasodilation of the microvasculature. However, whether a similar impairment is also present at the level of the conductance arteries is unknown.nnnMETHODSnTo this end, we studied endothelium-dependent (posthyperemia flow-mediated dilation) and -independent (nitroglycerin) vascular responses of the brachial artery by high-resolution ultrasound imaging. There were 46 black subjects (23 men and 23 women; age 37 +/- 8 years and 38 +/- 9 years, respectively) and 46 white subjects (23 men and 23 women; age 38 +/- 11 years and 36 +/- 9 years, respectively) in this study.nnnRESULTSnBaseline diameter was similar in blacks and in whites (4.4 +/- 0.9 mm and 4.1 +/- 0.7 mm, respectively). Mean reactive hyperemia after cuff deflation was similar in the two groups (793 +/- 653% in black and 852 +/- 734% in white subjects, respectively; p = 0.5). Flow-mediated dilation was significantly lower in black compared with white individuals (4.79 +/- 3.5% vs. 8.87 +/- 4.5%, respectively; p < 0.0001). Nitroglycerin-mediated dilation was also significantly lower in black individuals compared with white individuals (10.99 +/- 4.6% vs. 14.98 +/- 5.4%, respectively; p = 0.0002).nnnCONCLUSIONSnAfrican Americans show reduced responsiveness of conductance vessels to both endogenous and exogenous NO compared with Caucasian Americans. These findings expand our understanding of racial differences in vascular function and suggest a mechanistic explanation for the increased incidence and severity of cardiovascular disease observed in African Americans.

Attenuation of Cyclic Nucleotide–Mediated Smooth Muscle Relaxation in Blacks as a Cause of Racial Differences in Vasodilator Function

BACKGROUNDnVasodilator reactivity is attenuated in normotensive blacks, and this may contribute to their enhanced susceptibility to hypertension and its complications. However, the mechanisms responsible for this phenomenon are unknown. We therefore studied nitric oxide (NO)-dependent and -independent vasorelaxation in healthy blacks and whites to investigate the nature of racial differences in vasodilator function.nnnMETHODS AND RESULTSnForearm flow responses to intra-arterial infusion of increasing doses of acetylcholine (a vasodilator that stimulates endothelial release of NO), sodium nitroprusside (an exogenous NO donor), and isoproterenol (a beta-adrenergic agonist whose vasodilator effect stems from the combination of direct smooth muscle stimulation and endothelial NO release) were studied in 18 normotensive whites and 18 blacks by use of strain-gauge plethysmography. A blunted vasodilator response to acetylcholine (7.2+/-1.1 versus 14.4+/-1.8 mL. min-1. dL-1; P<0.001) and sodium nitroprusside (8.2+/-1.1 versus 12.1+/-1.3 mL. min-1. dL-1; P<0.001) was observed in blacks compared with whites, suggesting decreased cGMP-mediated smooth muscle relaxation. The vasodilator effect of isoproterenol was lower in blacks than in whites both before (10.9+/-1.7 versus 14.9+/-1.5 mL. min-1. dL-1; P=0.006) and after NG-monomethyl-L-arginine (6.1+/-1.2 versus 10. 1+/-0.8 mL. min-1. dL-1; P<0.001), implying that cAMP-dependent vasodilator response to isoproterenol is diminished in blacks. No significant difference was observed in the hyperemic response to forearm ischemia.nnnCONCLUSIONSnCompared with whites, healthy blacks have reduced vasodilation in response to NO-dependent and -independent stimuli. This difference seems to be related to an attenuation in cyclic nucleotide-mediated vascular smooth muscle relaxation and may play a role in the increased prevalence of hypertension and its complications in blacks.

Increased activity of endogenous endothelin in patients with hypercholesterolemia

OBJECTIVEnWe sought to assess the activity of endogenous endothelin-1 (ET-1) in hypercholesterolemic patients using antagonists of ET-1 receptors.nnnBACKGROUNDnEndothelial dysfunction in hypercholesterolemic patients may contribute to their risk of premature atherosclerosis. Endothelin, a peptide released by endothelial cells, may be involved in this process by activating smooth muscle cell mitogenesis and leukocyte adhesion.nnnMETHODSnForearm blood flow (FBF) responses (strain-gauge plethysmography) to intra-arterial infusion of a selective blocker of ETA receptors (BQ-123) and, on a separate occasion, to ET-1 were measured in 12 hypercholesterolemic patients and 12 normal control subjects. In addition, on a different day, six hypercholesterolemic patients received co-infusion of BQ- 123 and BQ-788 (a selective blocker of ETB receptors).nnnRESULTSnIn normal subjects, BQ-123 did not significantly modify FBF from baseline (p = 0.78); however, in hypercholesterolemic patients, BQ-123 administration resulted in a significant vasodilator response (p < 0.001). Administration of exogenous ET-1 resulted in similar vasoconstrictor responses in patients (37%) and control subjects (35%) (p = 0.83). In hypercholesterolemic patients, the vasodilator response to selective ETA blockade was reversed by nonselective blockade of ET-1 receptors obtained by co-infusion of BQ-123 and BQ-788.nnnCONCLUSIONSnThe vascular activity of endogenous ET-1 is enhanced in hypercholesterolemic patients, whereas their sensitivity to exogenous ET-1 is unchanged. These findings suggest increased production of ET-1, which may participate in the pathophysiology of vascular disease characteristic of hypercholesterolemia.

Decreased Vasodilator Response to Isoproterenol During Nitric Oxide Inhibition in Humans

The vasodilator effect of beta-adrenergic agonists has traditionally been ascribed solely to a direct effect on vascular smooth muscle. Experimental studies, however, have suggested a role of endothelium-derived nitric oxide (NO) in beta-adrenergic-mediated vasodilation. The purpose of this investigation was to determine whether NO contributes to the vasodilator effect of beta-adrenergic stimulation in humans. We analyzed the forearm blood flow response to increasing doses of isoproterenol (50, 100, and 200 ng/min), a beta-adrenoceptor agonist, during the concomitant infusion of saline or N(G)-monomethylL-arginine (L-NMMA; 4 micromol/min), a blocker of NO synthesis, in 23 normal subjects (9 men and 14 women, aged 48 +/- 7 years). The effect of L-NMMA was also assessed during infusion of sodium nitroprusside (0.8, 1.6, and 3.2 microg/min), an exogenous NO donor. Drugs were infused into the brachial artery, and forearm blood flow was measured by plethysmography. The vasodilator effect of isoproterenol was significantly blunted during the administration of L-NMMA compared with saline (maximum flow, 7.7 +/- 4 versus 11.2 +/- 5 mL x min(-1) x dL(-1), respectively; P<.001). In contrast, the vasodilator response to sodium nitroprusside was not significantly affected by the infusion of L-NMMA (maximum flow, 8.8 +/- 3.7 mL x min(-1) x dL(-1) during L-NMMA versus 8.9 +/- 3.2 mL x min(-1) x dL(-1) during saline; P=.25). These findings indicate that NO inhibition blunts the vasodilator effect of beta-adrenergic agonists in the human forearm and suggest that an abnormal response to adrenergic stimulation may occur in conditions associated with impaired NO activity.