Pharmacological Mechanisms of Clinically Favorable Properties of a Selective β1‐Adrenoceptor Antagonist,Nebivolol

Nebivolol is a racemic mixture of d‐ and 1‐enantiomers. The drug is characterized by β₁‐adrenoceptor selectivity and long‐acting β₁‐blockade exerted predominantly by d‐enantiomer. Nebivolol is devoid of intrinsic sympathomimetic activity and has no relevant membrane stabilizing action. Antiproliferative properties of nebivolol were demonstrated in endothelial and smooth muscle cell cultures. Infusion of nebivolol causes a vasodilation in all vascular beds by endothelial‐dependent mechanism involving stimulation of β₃‐adrenoceptors as well as by endothelial‐independent mechanism. Nebivolol possesses not only direct vasodilator properties but also augments the action of endothelium‐dependent vasodilators. The antioxidant property of nebivolol can at least in part explain why treatment with this drug enhances eNOS activity and minimizes the reperfusion‐induced myocardial injury. The systemic effects of nebivolol in humans have an unusual hemodynamic profile. In contrast to traditional β‐adrenoceptor antagonists, nebivolol reduces preload and afterload due to systemic vasodilation and improves arterial distensibility. At 5 mg daily nebivolol effectively reduces systolic and diastolic blood pressure over a 24‐h period. During treatment with nebivolol arterial pressure follows the natural circadian rhythm. Trough‐to‐peak ratio for nebivolol is 0.9. It has been demonstrated in numerous placebo‐controlled studies that exercise tolerance is not reduced during nebivolol therapy. By chronic administration to patients with left ventricular dysfunction nebivolol increases myocardial contractility. Nebivolol produced no significant changes in lipid levels, insulin sensitivity or glucose tolerance. These findings make nebivolol a promising therapeutic tool for the treatment of arterial hypertension and chronic heart failure.     

Improvement of left ventricular diastolic function induced by β-blockade: a comparison between nebivolol and metoprolol

Objectives

Enhanced adrenergic drive is involved in the development of left ventricular (LV) diastolic dysfunction observed in metabolic syndrome (MS). Thus, β-blockers might improve LV dysfunction observed in MS, but whether this occurs is unknown.

Methods

We assessed in Zucker fa/fa rats the effects of short- (5 days) and long-term (90 days) metoprolol (‘pure’ β-blockade; 80 mg/kg/day) or nebivolol (β-blocker with vasodilating properties; 5 mg/kg/day) treatment on LV hemodynamics and remodeling, as well as the long-term effects on coronary and peripheral endothelial dysfunction.

Results

At identical degree of β₁-receptor blockade, metoprolol and nebivolol decreased heart rate to the same extent and preserved cardiac output via increased stroke volume. None of the β-blockers, either after long- or short-term administration, modified LV end-systolic pressure-volume relation. Both β-blockers reduced, after long-term administration, LV end-diastolic pressure, Tau and end-diastolic pressure-volume relation, and this was associated with reduced LV collagen density, but not heart weight. Similar hemodynamic effects were also observed after short-term nebivolol, but not short-term metoprolol. These short-term effects of nebivolol were abolished by NO synthase inhibition. At the vascular level, nebivolol, and to a lesser extend metoprolol, improved NO dependent coronary vasorelaxation, which was abolished by NO synthase inhibition.

Conclusions

In a model of MS, the β-blockers metoprolol and nebivolol improve to the same extent LV hemodynamics, remodeling and diastolic function, but nebivolol prevent more markedly endothelium dependent vasorelaxation involving a more marked enhancement of NO bio-availability.     

Valsartan Improves Endothelial Dysfunction in Hypertension: A Randomized,Double‐Blind Study

Endothelial dysfunction can predict cardiac outcomes in hypertension and reversing this abnormality has become an attractive therapeutic objective. We tested the hypothesis that blocking the angiotensin type 1 (AT₁) receptor with valsartan in comparison with amlodipine would lead to an improvement in forearm resistance artery endothelial dysfunction. In total, 25 hypertensive subjects (mean age 60 years, SD 8) with a mean daytime ambulatory blood pressure (BP) of 154 (10)/97 (6) mmHg were randomized following a 3‐week placebo run‐in period to a double‐blind, crossover trial of 16‐week treatment periods with either valsartan or amlodipine, separated by a 3‐week washout period. Intra‐arterial infusions of acetylcholine (ACh) and N^G‐monomethyl‐L‐arginine (L‐NMMA) were used to assess stimulated and basal endothelium‐dependent nitric oxide (NO) release, respectively. Coinfusion of ACh and L‐NMMA was employed to investigate the existence of an NO‐independent vasodilatory pathway. Valsartan and amlodipine each lowered the clinical BP to the same extent (139 [7]/87 [6] and 139 [11]/89 [4] mmHg, respectively). The vasodilatory response to ACh was significantly increased with valsartan (maximal percentage change in forearm blood flow (max. ΔFBF%) 301 [47] vs. 185 [34], mean [SEM]; P < 0.05) as compared with placebo, but remained unchanged with amlodipine. Both valsartan and amlodipine similarly increased the vasoconstrictive response to L‐NMMA (max. ΔFBF%–43 [5], ?42 [5], respectively, vs. –26 [3] baseline; P < 0.001). The vasodilatory response after coinfusion of ACh and L‐NMMA was significantly (P < 0.05) enhanced only with valsartan. Valsartan reserved peripheral endothelial dysfunction through both NO‐dependent and ‐independent pathways, while for the same degree of BP control, amlodipine had only a partial effect on NO bioactivity.     

Oxidative Stress Impairs Endothelial Function in Nondipper Hypertensive Patients

Aims: Essential hypertension, as well as other established cardiovascular risk factors, is associated with endothelial dysfunction. Hypertensive patients with a nondipper circadian pattern have a greater risk of cerebrovascular and cardiovascular complications in comparison with those with a dipper circadian pattern. In this study, we evaluated the association between nondipper pattern and endothelial function in patients with essential hypertension. Methods: We evaluated the forearm blood flow (FBF) response to intraarterial acetylcholine (ACh), an endothelium‐dependent vasodilator, and sodium nitroprusside (SNP), an endothelium‐independent vasodilator, infusions in 190 hypertensive patients stratified according to dipper and nondipper status. The FBF was measured by strain‐gauge plethysmography. Effects of oxidative stress on FBF were evaluated by intraarterial infusion of vitamin C. Ambulatory BP monitorings were obtained by a validated oscillometric device (SpaceLabs 90207 Monitor Inc., Issaquah, WA, USA). Results: Systolic and diastolic blood pressures were higher during daytime and lower during night‐time in dipper subjects than in nondippers. The peak percent increase in ACh‐stimulated FBF was higher in dippers than in nondippers (473% vs. 228%, P < 0.001). The FBF responses to SNP were similar in dipper and nondipper patients. The FBF response to ACh during coinfusion of vitamin C was higher in nondippers rather than in dipper hypertensives. Conclusions: Present data demonstrate that endothelium‐dependent vasodilation is impaired in patients who have nondipper hypertension. The effects of vitamin C on impaired ACh‐stimulated vasodilation support the hypothesis that oxidative stress contributes to endothelial dysfunction of nondipper hypertensive patients.     

Long-term treatment with eicosapentaenoic acid improves exercise-induced vasodilation in patients with coronary artery disease.

We have previously shown that long-term treatment with eicosapentaenoic acid (EPA) improves endothelium-dependent vasodilation of the atherosclerotic arteries in both animals and humans. The aim of the present study was to examine whether EPA treatment also improves metabolic vasodilation evoked by exercise in patients with coronary artery disease (CAD). Forearm blood flow (FBF) was measured by strain gauge plethysmography in 10 patients with stable CAD, before and 3 months after oral treatment with EPA (1,800 mg/kg). FBF was measured at rest and during intra-arterial infusion of acetylcholine or sodium nitroprusside, before and after intra-arterial infusion of NG-monomethyl-L-arginine (L-NMMA, an inhibitor of nitric oxide (NO) synthesis). A rhythmic handgrip exercise was also performed for 3 min before and after L-NMMA, and FBF was measured for 3 min just after the handgrip exercise. These protocols were repeated after the long-term treatment with EPA for 3 months. The long-term treatment with EPA significantly improved the FBF responses to acetylcholine (p < 0.01), which was significantly reduced by acute administration of L-NMMA (p < 0.01). By contrast, the EPA treatment did not affect the endothelium-independent responses to sodium nitroprusside. Metabolic increases in FBF caused by the handgrip exercise were not significantly decreased by L-NMMA before the EPA treatment. The EPA treatment significantly augmented the exercise-induced increases in FBF (p < 0.05) and L-NMMA acutely abolished this augmentation (p < 0.01). These results indicate that long-term treatment with EPA improves both endothelium-dependent and exercise-induced forearm vasodilations in patients with CAD and that NO is substantially involved in the EPA-induced improvement of the FBF responses in patients with CAD.     

Metabolic vasodilation in the human forearm is preserved in hypercholesterolemia despite impairment of endothelium-dependent and independent vasodilation

OBJECTIVE: Hypercholesterolemia has been shown to impair endothelium-mediated, nitric oxide (NO)-dependent responses to acetylcholine (ACh), serotonin, substance P and flow-mediated dilation. We have recently shown that NO contributes to metabolic vasodilation in the human forearm. We sought to determine whether metabolic vasodilation is impaired in healthy subjects with hypercholesterolemia. METHODS: We compared the forearm blood flow (FBF) responses to isotonic exercise, ACh and the endothelium-independent vasodilator sodium nitroprusside in young, otherwise healthy volunteers with hypercholesterolemia and controls before and after the NO inhibitor NG-monomethyl-L-arginine (L-NMMA). FBF was measured using venous occlusion plethysmography. Hypercholesterolemic (n = 20) and control (n = 20) subjects were age- and gender-matched. RESULTS: Total cholesterol (6.9 +/- 0.3 vs. 4.6 +/- 0.1 mmol/l, P < 0.0001), low density lipoprotein (4.9 +/- 0.4 vs. 2.7 +/- 0.1 mmol/l, P < 0.001) and triglyceride (1.3 +/- 0.2 vs. 0.8 +/- 0.1 mmol/l, P = 0.005) levels were higher in the hypercholesterolemic group. Basal FBF and resistance were similar in the two groups. Hypercholesterolemia impaired the peak FBF response to ACh (11.1 +/- 1.9 vs. 17.6 +/- 2.2 ml/100 ml/min, P = 0.03), and reduced the peak response to sodium nitroprusside (6.0 +/- 0.4 vs. 8.1 +/- 0.6 ml/100 ml/min, P < 0.01). However, hypercholesterolemia did not affect peak hyperemic FBF (13.1 +/- 1.0 vs. 13.2 +/- 1.0 ml/100 ml/min, P = 1.0) or the FBF volume repayment during the 1 or 5 min after exercise. Resting FBF was reduced by L-NMMA to a similar degree (by 33% vs. 40%, P = 0.17) in both groups. Although L-NMMA reduced peak hyperemic FBF (by 16% vs. 17%, P = 0.93) and the volume repaid after exercise in both groups, there were no differences between the two groups. CONCLUSIONS: Exercise-induced metabolic vasodilation is in part dependent on NO release. Hypercholesterolemia impairs NO-mediated vasodilation, but is not associated with a reduction in exercise-induced hyperemia. This may indicate that multiple compensatory mechanisms are operative in skeletal muscle metabolic vasodilation.     

Nebivolol Effects on Nitric Oxide Levels,Blood Pressure,and Renal Function in Kidney Transplant Patients

In hypertensive kidney transplant recipients, the effects of nebivolol vs metoprolol on nitric oxide (NO) blood level, estimated glomerular filtration rate (eGFR), and blood pressure (BP) have not been previously reported. In a 12‐month prospective, randomized, open‐label, active‐comparator trial, hypertensive kidney transplant recipients were treated with nebivolol (n=15) or metoprolol (n=15). Twenty‐nine patients (nebivolol [n=14], metoprolol [n=15]) completed the trial. The primary endpoint was change in blood NO level after 12 months of treatment. Secondary endpoints were changes in eGFR, BP, and number of antihypertensive drug classes used. After 12 months of treatment, least squares mean change in plasma NO level in the nebivolol kidney transplant recipient group younger than 50 years was higher by 68.19% (99.17% confidence interval [CI], 13.02–123.36), 69.54% (99.17% CI, 12.71–126.37), and 66.80% (99.17% CI, 12.95–120.64) compared with the metoprolol group younger than 50 years, the metoprolol group 50 years and older, and the nebivolol group 50 years and older, respectively. The baseline to month 12 change in mean arterial BP, eGFR, and number of antihypertensive drug classes used was not significantly different between the treatment groups. In hypertensive kidney transplant recipients, nebivolol use in patients younger than 50 years increased blood NO.     

Effect of AT1 receptor blockade on endothelial function in essential hypertension

BACKGROUND: Angiotensin II adversely affects endothelial function and NO availability. We analyzed the effect of AT(1) receptor blockade on endothelium-dependent vasodilation and basal nitric oxide (NO) production and release in hypertensive patients. METHODS AND RESULTS: Sixty patients (53 +/- 10 years) with essential hypertension were randomized to 6 weeks of double-blind therapy with either valsartan (80 mg), hydrochlorothiazide (HCTZ) (25 mg), or placebo once daily. Basal NO production and release was assessed by measuring forearm blood flow (FBF) in response to intra-arterial infusion of N(G)-monomethyl-L-arginine (L-NMMA), and endothelium-dependent vasodilation by measuring FBF in response to intra-arterial administration of acetylcholine, respectively. Intra-arterial infusion of noradrenaline and sodium nitroprusside was used to assess endothelium-independent changes in FBF. Blood pressure (BP) similarly decreased with active treatments (P < .001). After valsartan treatment, the decrease of FBF in response to L-NMMA was augmented (4 micromol/min L-NMMA, -1.3 +/- 1.2 after v -0.5 +/- 1.1 mL/min/100 mL before therapy, P < .02; 8 micromol/min L-NMMA: -1.7 +/- 1.3 after v -1.1 +/- 1.2 mL/min 100 mL before therapy, P < .05). No improvement was found after placebo or HCTZ treatment. Changes in L-NMMA-induced decrease of FBF with valsartan treatment were not related to BP changes. Neither drug substantially modified the response of FBF induced by intra-arterial infusion of acetylcholine, noradrenaline, and sodium nitroprusside. CONCLUSIONS: The AT(1) receptor blockade with valsartan improved basal NO production and release. The effect seems to be BP independent, as BP reduction with HCTZ failed to increase NO availability.     

Bradykinin-induced vasodilation of human forearm resistance vessels is primarily mediated by endothelium-dependent hyperpolarization

Bradykinin (BK) stimulates endothelial cells to release a number of relaxing factors, such as NO, prostanoids (PGs), and an endothelium-derived hyperpolarizing factor (EDHF). However, the contributions of NO, PG, and EDHF in the vascular relaxation to BK vary with species and anatomic origin of blood vessels used. Therefore, the present study was designed to investigate the contributions of NO, PG, and EDHF in vasodilation caused by BK in human forearm resistance vessels. Forearm blood flow (FBF) was recorded with venous occlusion plethysmography in healthy nonsmoking subjects. At first, studies were performed to validate the NO clamp technique for its ability to inhibit endogenous NO generation. Brachial artery infusion of serotonin (0.6, 1.8, and 6 ng. 100 mL forearm volume [FAV](-1). min(-1)) caused significant forearm vasodilation (2.6 to 4.6 mL. 100 mL FAV(-1). min(-1)), which is known to be NO mediated. Indeed, during the NO clamp, cumulative doses of serotonin caused no vasodilation (2.4 to 2.6 mL. 100 mL FAV(-1). min(-1)), indicating that the generation of endogenous NO was completely blocked. Thereafter, the vasodilative actions of BK were investigated. Brachial artery infusion of BK (50, 100, and 200 ng. 100 mL FAV(-1). min(-1)) caused significant forearm vasodilation in all studies (from 3.1 to 20.4 mL. 100 mL FAV(-1). min(-1)). After the inhibition of cyclooxygenase and NO synthase activity through the use of aspirin and the NO-clamp technique, BK increased FBF in a similar manner (3.9 to 18.9 mL. 100 mL FAV(-1). min(-1)), indicating that the vasodilative actions of BK are independent of NO and PG generation. However, vasodilation caused by the 2 lower doses of BK were significantly attenuated after K(Ca) channel activity was blocked with tetraethylammonium chloride (0.1 mg. 100 mL FAV(-1). min(-1)), suggesting that in the lower dose range, BK mediates vasodilation through the opening of vascular potassium channels. In conclusion, BK is a potent vasodilator peptide in human forearm resistance vessels, causing vasodilation through hyperpolarization of the vascular wall independent of NO and PG production. In addition, the NO-clamp technique is a valid instrument to investigate the contribution of NO in the vasodilative response to different agents.     

Effects of central administration of insulin or l-NMMA on rat skeletal muscle microvascular perfusion

Aim: Intracerebroventricular (ICV) administration of a nitric oxide synthase (NOS) inhibitor to rats has been reported to raise blood pressure (BP) and cause insulin resistance, suggestive of a central effect of insulin that is NO dependent. Herein we test whether ICV insulin has peripheral haemodynamic and metabolic effects and whether peripheral effects of systemic insulin are affected by the ICV administration of the NOS inhibitor N^G‐methyl‐l ‐arginine (l ‐NMMA). Methods: Anaesthetized rats were fitted with an ICV cannula for insulin, artificial cerebrospinal fluid (aCSF) or l ‐NMMA infusion. Rats receiving ICV l ‐NMMA (500 µg) underwent systemic insulin clamp (10 mU/min/kg) or saline treatment for 70 min and were compared with animals receiving an equal amount of l ‐NMMA infused systemically. Results: ICV aCSF or insulin (135 mU/min/kg brain) for 70 min or systemic l ‐NMMA (500 µg) had no effect on BP, heart rate (HR), femoral blood flow (FBF), glucose infusion rate, muscle 2‐deoxyglucose uptake, microvascular perfusion or plasma insulin. However, ICV l ‐NMMA reduced systemic insulin‐mediated increases in FBF (2.05 ± 0.08 to 1.55 ± 0.15 ml/min), 2‐deoxyglucose uptake (17.7 ± 0.15 to 10.0 ± 0.03 µg/g/min) and microvascular perfusion (10.5 ± 0.5 to 6.6 ± 1.1 mol/min) (each mean ± SE, p < 0.05); plasma insulin, HR and BP were unaffected. Conclusions: Central insulin administration had no effect on skeletal muscle haemodynamics or glucose metabolism. However, systemic insulin‐mediated increases in limb blood flow, muscle microvascular perfusion and glucose uptake may be regulated by a central pathway that is NO dependent.     

Nebivolol induces nitric oxide release in the heart through inducible nitric oxide synthase activation

Nebivolol is a beta1-adrenergic receptor antagonist that also reduces blood pressure by evoking endothelial NO production and vasodilation. We aimed at assessing whether nebivolol induces NO production also in the heart and delineating the molecular mechanisms involved. Using the fluorescent probe diaminofluorescein, we found that nebivolol induces a dose-dependent NO production in the heart, statistically significant already at 10(-7) mol/L. It is not an effect because of the blockade of beta1-adrenergic receptor, because this effect is not shared by another drug of the same class, atenolol. Because nebivolol has been reported to act as an agonist on other beta-adrenergic receptors, we tested NO production in the presence of receptor antagonists. Nebivolol was not able to induce NO production in presence of the beta3-antagonist SR59230A, indicating a fundamental role for beta3-adrenergic receptors in cardiac NO production by nebivolol. Moreover, inducible NO synthase inhibition abolishes NO release in the heart, indicating that nebivolol induces NO production by acting on the inducible isoform of the enzyme. The action of nebivolol on inducible NO synthase was confirmed by real-time PCR experiments, showing cardiac overexpression of inducible NO synthase but not neuronal NO synthase or endothelial NO synthase, after 5 hours of treatment with nebivolol. In conclusion, our study demonstrates that nebivolol also stimulates NO production in the heart. This action of nebivolol is exerted via a signaling pathway starting from the activation of beta3-adrenergic receptors and leading to overexpression of inducible NO synthase. Cardiac NO production by nebivolol could participate in the cardiovascular effects of nebivolol treatment in patients affected by hypertension and heart failure.     

Cardio‐selective and non‐selective beta‐blockers in chronic obstructive pulmonary disease: effects on bronchodilator response and exercise

Background: Patients with chronic obstructive pulmonary disease (COPD) often have co‐existing cardiovascular disease and may require beta‐blocker treatment. There are limited data on the effects of beta‐blockers on the response to inhaled β₂‐agonists and exercise capacity in patients with COPD. Objective: To determine the effects of different doses of cardio‐selective and non‐selective beta‐blockers on the acute bronchodilator response to beta‐agonists in COPD, and to assess their effects on exercise capacity. Methods: A double‐blind, randomized, three‐way cross‐over (metoprolol 95 mg, propranolol 80 mg, placebo) study with a final open‐label high‐dose arm (metoprolol 190 mg). After 1 week of each treatment, the bronchodilator response to salbutamol was measured after first inducing bronchoconstriction using methacholine. Exercise capacity was assessed using the incremental shuttle walk test. Results: Eleven patients with moderate COPD were recruited. Treatments were well‐tolerated although two did not participate in the high‐dose metoprolol phase. The area under the salbutamol–response curve was lower after propranolol compared with placebo (P = 0.0006). The area under the curve also tended to be lower after high‐dose metoprolol (P = 0.076). The per cent recovery of the methacholine‐induced fall was also lower after high‐dose metoprolol (P = 0.0018). Low‐dose metoprolol did not alter the bronchodilator response. Oxygen saturation at peak exercise was lower with all beta‐blocker treatments (P = 0.046). Conclusion: Non‐selective beta‐blockers and high doses of cardio‐selective beta‐blockers may inhibit the bronchodilator response to β₂‐agonists in patients with COPD. Beta‐blockers were also associated with lower oxygen saturation during exercise. The clinical significance of these adverse effects is uncertain in view of the benefits of beta‐blocker treatment for cardiovascular disease.     

The Effect of Low‐Dose Carvedilol,Nebivolol, and Metoprolol on Central Arterial Pressure and Its Determinants: A Randomized Clinical Trial

In this prospective, open‐label, randomized, controlled clinical trial the effects of low‐dose carvedilol, nebivolol, and metoprolol on central arterial pressure and augmentation index (AIx) and its heart rate–corrected value (AIx@75) were assessed. The authors randomized 75 hypertensive patients (18–70 years) to carvedilol 12.5/25 mg, metoprolol 50/100 mg, or nebivolol 2.5/5 mg daily and followed them up for 3 months. Central arterial pressure and AIx were measured with applanation tonometry at baseline and at the end of follow‐up. Analyses were restricted to 60 completers. Central systolic pressure decreased equally in all 3 treatment arms. AIx remained unchanged, while AIx@75 decreased significantly by 5.4%±2.5% in the nebivolol group. According to general linear models, individual change in heart rate was a strong predictor of change in AIx in the carvedilol group (r²=0.23, P=.03) although no similar association was found in the nebivolol group (r²=0.09). The impact of β‐blockers with vasodilator effects on pressure augmentation seems to be different with nebivolol having the largest potential of decreasing AIx@75. While AIx changes associated with carvedilol treatment are strongly driven by heart rate changes, those associated with nebivolol treatment seem to be the result of other mechanisms.     

Acute moderate-intensity exercise induces vasodilation through an increase in nitric oxide bioavailiability in humans

BACKGROUND: Long-term moderate-intensity exercise augments endothelium-dependent vasodilation through an increase in nitric oxide (NO) production. The purpose of this study was to determine the effects of different intensities of acute exercise on hemodynamics in humans. METHODS: We evaluated forearm blood flow (FBF) responses to different intensities of exercise (mild, 25% maximum oxygen consumption [VO2max]; moderate, 50% VO2max; and high, 75% VO2max; bicycle ergometer, for 30 min) in eight healthy young men. The FBF was measured by using a strain-gauge plethysmography. RESULTS: After exercise began, moderate-intensity exercise, but not mild-intensity exercise, promptly increased FBF from 2.8+/-1.1 mL/min/100 mL to a plateau at 5.4+/-1.6 mL/min/100 mL at 5 min (P<.01) and increased mean arterial pressure from 84.7+/-11.8 mm Hg to a plateau at 125.7+/-14.3 mm Hg at 5 min (P<.01). Moderate-intensity exercise decreased forearm vascular resistance (FVR) from 29.2+/-5.4 to 16.8+/-3.2 mm Hg/mL/min/100 mL tissue (P<.01). The administration of NG-monomethyl-L-arginine, an NO synthase inhibitor, abolished moderate exercise-induced augmentation of vasodilation. Although we were not able to measure FBF during high-intensity exercise because of large body motion, high-intensity exercise markedly increased mean arterial pressure from 82.6+/-12.2 to 146.8+/-19.8 mm Hg. High-intensity exercise, but not mild-intensity or moderate-intensity exercise, increased plasma concentration of 8-isoprostane, an index of oxidative stress, from 24.1+/-10.8 to 40.2+/-16.7 pg/mL (P<.05) at 10 min after the end of exercise. CONCLUSIONS: These findings suggest that acute moderate-intensity exercise induces vasodilation through an increase in NO bioavailability in humans and that high-intensity exercise increases oxidative stress.     

Role of endothelium-derived hyperpolarizing factor in human forearm circulation

Endothelium-derived hyperpolarizing factor (EDHF) contributes to endothelium-dependent relaxation of isolated arteries, but it is not known whether this also occurs in the case of humans in vivo. The present study examined the role of EDHF in human forearm circulation. Forearm blood flow (FBF) was measured by strain-gauge plethysmography in 31 healthy, normal subjects (mean+/-SE age, 23+/-2 years; 24 men and 7 women). After oral administration of aspirin (486 mg), we infused NG-monomethyl-L-arginine (8 micromol/min for 5 minutes) into the brachial artery. We used tetraethylammonium chloride (TEA, 1 mg/min for 20 minutes), a KCa channel blocker, as an EDHF inhibitor, and nicorandil as a direct K+ channel opener. TEA significantly reduced FBF (P<0.05) but did not change systemic arterial blood pressure. Furthermore, TEA significantly inhibited the FBF increase in response to substance P (0.8, 1.6, 3.2, and 6.4 ng/min, n=8) and bradykinin (12.5, 25, 50, and 100 ng/min, n=8; both P<0.001), whereas it did not affect the FBF increase in response to acetylcholine (4, 8, 16, and 32 microg/min, n=8), sodium nitroprusside (0.4, 0.8, 1.6, and 3.2 microg/min, n=8), or nicorandil (0.128, 0.256, 0.512, and 1.024 mg/min, n=8). These results suggest that EDHF contributes substantially to basal forearm vascular resistance, as well as to forearm vasodilatation evoked by substance P and bradykinin in humans in vivo.     

Involvement of NO and EDHF in flow-induced vasodilation in isolated hamster cremasteric arterioles

Flow-induced vasodilation in hamster cremasteric arterioles was investigated with special reference to the roles of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). Arterioles (approximately 60 microm resting diameter) were cannulated, and suffused with MOPS solution at 37 degrees C (mean intraluminal pressure: 80 cm H(2)O). Step increases in the perfusate flow elicited a dose-dependent vasodilation, which was almost proportional to the increases in calculated wall shear stress (WSS). N(omega)-nitro L-arginine methyl ester (L-NAME, 100 microM) reduced the flow-induced vasodilation by approximately 50%, whereas indomethacin (10 microM) produced no significant effect. In the presence of L-NAME, the residual vasodilation was eliminated by treatment with the cytochrome P-450 monooxygenase inhibitor 17-octadecynoic acid (17-ODYA, 50 microM), sulfaphenazol (10 microM), tetraethylammonium (TEA, 3 mM; a nonselective Ca(2+)-activated K(+) channel inhibitor), or charybdotoxin (ChTX, 0.1 microM; intermediate or large conductance Ca(2+)-activated K(+) channel inhibitor). In the absence of L-NAME, the dilation was also reduced by approximately 50% by treatment with 17-ODYA, TEA, or ChTX. The residual vasodilation was eliminated by additional treatment with L-NAME. The inhibitor of ATP-sensitive K(+) channels (K(ATP)), glibenclamide, also caused a significant, but partial, reduction of the flow-induced vasodilation. The residual vasodilation was completely reduced by additional treatment with 17-ODYA, but not L-NAME. These findings suggest that in hamster cremaster, higher flow rate produces NO, K(ATP), and EDHF vasodilation of the arterioles under physiological conditions.     

Effect of beta-adrenergic blockade on hormonal responses during continuous and intermittent exercise

Summary The modifying effect on exercise performance and neuroendocrine response of the nonselective beta blocker timolol (10 mg b.i.d. for 5 days) and the beta₁-selective beta blocker metoprolol (100 mg b.i.d. for 5 days) was studied. The hormones studied were growth hormone, prolactin, cortisol, renin, epinephrine, dopamine, and norepinephrine. The response was studied during short-term maximal dynamic exercise, using two different exercise protocols; continuous (n=11) and intermittent (n=9) bicycle ergometry, in normal healthy young men. Accumulated work on placebo was nearly identical in the two studies, but was significantly reduced by 10.4% and 6.6% with timolol and by 4.7% and 6.7% with metoprolol, during continuous and intermittent exercise, respectively. During continuous exercise, accumulated work was 5.8% lower (p<0.05) with timolol than with metoprolol. The hormonal plasma concentrations of all hormones except renin were higher during continuous exercise than during intermittent exercise. Beta blockade had no effect on baseline hormonal levels, but the response was markedly changed during exercise. Maximum epinephrine, cortisol, and prolactin responses increased after beta blockade; dopamine remained nearly unchanged; while the renin responses were attenuated. Norepinephrine concentrations were slightly increased during continuous exercise by beta blockade and rose in direct proportion to the increase in workload. During intermittent exercise, maximum norepinephrine levels were significantly reduced by beta blockade compared with placebo. Thus the effect of beta₁-selective and nonselective beta receptor blockade on circulating hormones does not seem to explain the reduced exercise capacity following beta blockade.     

The Functional Consequence of the Glu298Asp Polymorphism of the Endothelial Nitric Oxide Synthase Gene in Young Healthy Volunteers

Objective—To assess the role of the endothelial nitric oxide synthase (eNOS) gene variant as a risk factor for atherosclerosis we sought to investigate whether the Glu298Asp polymorphism of the eNOS gene is associated with functional changes in the endothelium in healthy volunteers. Methods—Endothelial function was assessed in 68 normal volunteers (ages 18–44 years) by bilateral forearm venous occlusion plethysmography with intraarterial infusions of increasing doses of acetylcholine for endothelial-dependent vasodilation and, with sodium nitroprusside and verapamil for endothelial-independent vasodilation. Blood was genotyped by polymerase chain reaction and BanII digestion. Results—Asp homozygotes (TT) had a decreased vasodilatory response to acetylcholine [forearm blood flow (FBF) ratio between infused and control arm, 2.82 ± 1.10] when compared to GG variant (FBF ratio to acetylcholine, 3.97 ± 1.90, p= 0.04) and to a certain extent, the GT variant (FBF ratio to acetylcholine, 3.79 ± 2.28, p= 0.07). There was no effect of eNOS genotype on the response to the endothelial-independent vasodilators—sodium nitroprusside and verapamil. Conclusions—Our data show that carriage of the Asp298 variant of the eNOS gene is associated with a blunted endothelial-dependent vasodilation in healthy volunteers. These findings support a genetically determined modulation of endothelial dysfunction, a phenotype of early atherosclerosis in humans.     

Nitric oxide plays an insignificant role in direct vasodilator effects of calcium channel blockers in healthy humans

Several experimental studies have suggested that the vasodilatory effects of calcium channel blockers (CCBs) are due in part to an endothelium-dependent mechanism. However, it remains unknown whether CCBs directly augment liberation of endothelium-derived dilator substances such as nitric oxide (NO) in the human vasculature. The aim of this study was to examine whether CCBs of several kinds directly increase the bioavailability of NO in forearm resistance vessels. Twenty-four healthy men (mean age 30 ± 2 years) were randomly assigned to three study groups (n = 8 in each), and each group was assigned one of three first-generation CCBs (nifedipine, nicardipine, diltiazem). Subdepressor doses of CCBs [4, 8, 16, 24, and 36 (diltiazem only) nmol/min; for 2 min in each dose] were infused intra-arterially, and forearm blood flow (FBF) was determined plethysmographically. After control FBF responses to CCBs had been measured, a NO synthase inhibitor (N ^G-monomethyl-l-arginine: l-NMMA) was infused intra-arterially, and the FBF response to CCBs was again determined. Further, as a positive control for NO stimulation, acetylcholine (ACh) was also examined before and after l-NMMA in each group. Systemic blood pressure and heart rate did not change significantly during the study protocol. The FBF responses to these CCBs did not differ before and after NO synthase inhibition by l-NMMA (FBF at maximum doses: nifedipine, 8.0 ± 0.8 vs 7.3 ± 0.7; nicardipine, 7.3 ± 1.5 vs 6.5 ± 1.3; diltiazem, 5.7 ± 0.7 vs 4.2 ± 0.7 ml/min per 100 ml: all not significant), although FBF responses to ACh were significantly reduced by l-NMMA. In conclusion, direct NO liberation does not make a significant contribution to the vasodilation associated with first-generation CCBs in healthy human resistance vessels. Received: July 12, 2001 / Accepted: October 19, 2001     

Effects of Nebivolol on Aortic Compliance in Patients With Diabetes and Maximal Renin Angiotensin System Blockade: The EFFORT Study

The beneficial effects of nebivolol on arterial stiffness and endothelial dysfunction are well documented in untreated hypertensive patients and differ from nonvasodilatory β‐blockers. This study tests the hypothesis that the addition of nebivolol in predominantly African American patients with type 2 diabetes already receiving maximally tolerated doses of renin‐angiotensin system (RAS) blockers will further improve large artery compliance. Patients with type 2 diabetes and hypertension on maximal RAS blockade (n=70) were randomized to nebivolol or metoprolol succinate daily. Doses were titrated until systolic blood pressure (SBP) was <130 mm Hg. Radial artery applanation tonometry and pulse wave velocity (PWV) analysis were used to derive central aortic pressures and hemodynamic indices at repeated visits at intervals during a 6‐month period. Both metoprolol succinate and nebivolol groups demonstrated reductions in brachial SBP (−8.2±4.3 mm Hg [P=.01] and −7.8±3.7 [P=.002], respectively) and aortic DBP (−2.4±1.8 [P=.039] and −4.0±2.9 mm Hg [P=.013], respectively). Aortic SBP decreased in the nebivolol group only (125.3±8 to 121.6±8.2, P=.025). There were no between group differences in aortic SBP, DBP, augmentation index, or PWV reduction. A significant increase in hemoglobin A_1c was observed only in the metoprolol group. In patients with well‐controlled type 2 diabetes and hypertension treated with maximally tolerated RAS blockade, nebivolol does not offer significant reductions in aortic BP over metoprolol succinate but maintains a stable metabolic profile.

Nebivolol, a highly selective β₁‐antagonist, has different chemical and mechanistic properties than previously developed β‐blockers. Compared with conventional β₁‐selective adrenergic receptor antagonists such as metoprolol succinate, nebivolol exerts additional vasodilatory properties by stimulating endothelial cell nitric oxide (NO) production¹, ² mediated by β₃‐receptor activation³ and interaction with the estrogen receptor.⁴ Nebivolol decreases oxidative stress in primary hypertension and increases NO bioavailability through upregulation of endothelial NO synthase (eNOS) and reduction of circulating asymmetric dimethylarginine (ADMA).⁵, ⁶ Nebivolol administration also restores NO bioavailability in endothelial cells obtained from African Americans who have an impaired release of NO to conventional stimuli.⁷ Central pressure is also more closely associated with cardiovascular (CV) outcomes relative to brachial blood pressure (BP).⁸ Increases in pulse wave velocity (PWV) indicating stiffer vessels are associated with increases in CV risk and chronic kidney disease (CKD) progression.⁹, ¹⁰, ¹¹ Data from the Conduit Artery Function Evaluation (CAFE) trial¹² show that agents that reduce central aortic as well as peripheral pressures are associated with a lower CV risk profile compared with agents that lower only peripheral pressures. Traditional β‐blockers, eg, atenolol or metoprolol, while reducing CV risk in people with coronary disease do not affect aortic stiffness compared with blockers of the renin‐angiotensin system (RAS). Vascular compliance studies comparing traditional β‐blockers with newer vasodilating β‐blockers in patients with type 2 diabetes on maximally dosed background RAS blockade have not been performed. Given that patients with diabetes have increased pulse wave velocities compared with age‐matched patients without diabetes¹³ and that African Americans have about a 50% lower response to stimuli of NO, the present study was designed to examine the effect of nebivolol therapy compared with metoprolol succinate therapy on peripheral and aortic arterial pressure as well as aortic compliance. The null hypothesis tested states that there will be no benefit on aortic compliance with nebivolol compared with metoprolol in the presence of maximally tolerated RAS therapy in a predominantly African American population with type 2 diabetes.