Role of digital artery adrenoceptors in Raynaud's disease

Raynaud's disease is characterized by excessive cutaneous vasoconstriction in response to ambient cold. A functional disturbance in the local regulation of digital vasomotion has been proposed. The purpose of this study was to determine whether there is an alteration in the postjunctional adrenergic receptors in the digital circulation of patients with Raynaud's disease. Furthermore, we sought to determine whether this abnormality was responsible for the excessive cold-induced vasoconstriction in these patients. Finger blood flow was measured by strain-gauge venous occlusion plethysmography in 10 patients with Raynaud's disease and in 10 normal volunteers in a 22 degrees C room. Measurements of finger blood flow and mean systemic arterial pressure were made during intra-arterial infusions of the alpha 1-adrenergic antagonist, prazosin, or the alpha 2-adrenergic antagonist, yohimbine, at room temperature and during local cooling of the hand. Basal finger blood flow in normal subjects was significantly greater than that of patients (8.6 +/- 2.7 vs 1.7 +/- 0.5 ml/100 ml per min; normal vs Raynaud's subjects; p < 0.05). In normal subjects, either prazosin or yohimbine induced dose-dependent increases in finger blood flow. The maximal increase in finger blood flow induced by prazosin was significantly greater than that in response to yohimbine (29.2 +/- 10.1 vs 2.8 +/- 2.1 ml/100 ml per min; prazosin vs yohimbine; p < 0.05). By contrast, in the Raynaud's patients, prazosin or yohimbine induced maximal increases in finger blood flow that were not significant (7.1 +/- 1.8 vs 5.0 +/- 2.2 ml/100 ml per min; prazosin vs yohimbine; p = NS). The response to prazosin in Raynaud's patients was significantly less than that of the normal volunteers (p < 0.05). In normal subjects, during intra-arterial infusion of vehicle alone, cooling induced a 52.6 +/- 5.8% reduction in finger blood flow. This cold-induced vasoconstriction was blunted, but not qualitatively altered, by either adrenergic antagonist. In the Raynaud's patients, during the intra-arterial infusion of the vehicle, cooling induced a 68.2 +/- 7.8% reduction in finger blood flow. Infusion of either adrenergic antagonist blunted, but did not qualitatively alter, the response to cold. Finger blood flow is less in patients with Raynaud's disease than in normal subjects when studied in a 22 degrees C room. In normal subjects, postjunctional alpha 1-adrenergic receptors appear to predominate in the control of digital vasoconstriction. Postjunctional alpha 1- and alpha 2-adrenoceptors play an equal role in adrenergic regulation of finger blood flow in patients with Raynaud's disease. In both normal and Raynaud's subjects, selective antagonism of alpha 1- or alpha 2-adrenergic receptors does not abolish local cold-induced vasoconstriction. Therefore, it is likely that a nonadrenergic mechanism contributes to local cold-induced vasoconstriction.

Estradiol therapy combined with progesterone and endothelium-dependent vasodilation in postmenopausal women

BACKGROUND

Epidemiological studies indicate that estrogen replacement therapy decreases the risk of cardiovascular events in postmenopausal women. Estrogen may confer cardiovascular protection by improving endothelial function because it increases endothelium-dependent vasodilation. It is not known whether progesterone attenuates the beneficial effects of estrogen on endothelial function.

METHODS AND RESULTS

Seventeen postmenopausal women with mild hypercholesterolemia were enrolled in a placebo-controlled, crossover trial to evaluate the effect of transdermal estradiol, with and without vaginal micronized progesterone, on endothelium-dependent vasodilation in a peripheral conduit artery. Brachial artery diameter was measured with high-resolution B-mode ultrasonography. To assess endothelium-dependent vasodilation, brachial artery diameter was determined at baseline and after a flow stimulus induced by reactive hyperemia. To assess endothelium-independent vasodilation, brachial artery diameter was measured after administration of sublingual nitroglycerin. During estradiol therapy, reactive hyperemia caused an 11.1+/-1.0% change in brachial artery diameter compared with 4. 7+/-0.6% during placebo therapy (P<0.001). Progesterone did not significantly attenuate this improvement. During combined estrogen and progesterone therapy, flow-mediated vasodilation of the brachial artery was 9.6+/-0.8% (P=NS versus estradiol alone). Endothelium-independent vasodilation was not altered by estradiol therapy, either with or without progesterone, compared with placebo. There was a modest decrease in total and LDL cholesterol during treatment both with estradiol alone and when estradiol was combined with progesterone (all P<0.001 versus placebo). In a multivariate analysis that included serum estradiol, progesterone, total and LDL cholesterol concentrations, blood pressure, and heart rate, only the estradiol level was a significant predictor of endothelium-dependent vasodilation.

CONCLUSIONS

The addition of micronized progesterone does not attenuate the favorable effect of estradiol on endothelium-dependent vasodilation. The vasoprotective effect of hormone replacement therapy may extend beyond its beneficial actions on lipids.

Aging progressively impairs endothelium-dependent vasodilation in forearm resistance vessels of humans

Studies in experimental models suggest that endothelium-derived nitric oxide is reduced with aging, and this circumstance may be relevant to atherogenesis. The aim of this study was to determine whether increasing age resulted in altered endothelium-dependent vasodilation in the forearm resistance vessels of healthy humans. Forearm blood flow was measured in 119 healthy subjects, aged 19 to 69 years, by venous occlusion plethysmography. Brachial artery infusions of methacholine chloride (0.03 to 10.0 microgram/min) were used to assess endothelium-dependent vasodilation and of sodium nitroprusside (0.03 to 10.0 microgram/min) to assess endothelium-independent vasodilation. The slope of the dose-blood flow response relation was calculated in each subject for each drug. Univariate and multiple stepwise regression analyses were used to relate vascular reactivity to selected variables, including age, lipids, and blood pressure. Endothelium-dependent vasodilation was progressively impaired with increasing age, assessed as a reduction in slope from 2.25 +/- 0.16 to 0.34 +/- 0.11 (mL/100 mL tissue per minute)/(microgram/min) (P <.001). The decline in endothelium-dependent vasodilation was already evident by the fourth decade (age 30 to 39 years). Endothelium-independent vasodilation did not change with age. Age, total cholesterol, and low-density lipoprotein cholesterol were univariate predictors of endothelium-dependent vasodilation. Age remained the most significant predictor of endothelium-dependent vasodilator responses by multiple stepwise regression analysis. From these observations, it can be concluded that endothelium-dependent vasodilation declines steadily with increasing age in healthy human subjects. Age is a strong univariate and multivariate predictor of endothelium-dependent vasodilation. This finding may be a marker for more widespread endothelial dysfunction.

Vitamin C improves endothelium-dependent vasodilation in patients with non-insulin-dependent diabetes mellitus

Endothelium-dependent vasodilation is impaired in humans with diabetes mellitus. Inactivation of endothelium-derived nitric oxide by oxygen-derived free radicals contributes to abnormal vascular reactivity in experimental models of diabetes. To determine whether this observation is relevant to humans, we tested the hypothesis that the antioxidant, vitamin C, could improve endothelium-dependent vasodilation in forearm resistance vessels of patients with non-insulin-dependent diabetes mellitus. We studied 10 diabetic subjects and 10 age-matched, nondiabetic control subjects. Forearm blood flow was determined by venous occlusion plethysmography. Endothelium-dependent vasodilation was assessed by intraarterial infusion of methacholine (0.3-10 micrograms/min). Endothelium-independent vasodilation was measured by intraarterial infusion of nitroprusside (0.3-10 micrograms/min) and verapamil (10-300 micrograms/min). Forearm blood flow dose-response curves were determined for each drug before and during concomitant intraarterial administration of vitamin C (24 mg/min). In diabetic subjects, endothelium-dependent vasodilation to methacholine was augmented by simultaneous infusion of vitamin C (P = 0.002); in contrast, endothelium-independent vasodilation to nitroprusside and to verapamil were not affected by concomitant infusion of vitamin C (P = 0.9 and P = 0.4, respectively). In nondiabetic subjects, vitamin C administration did not alter endothelium-dependent vasodilation (P = 0.8). We conclude that endothelial dysfunction in forearm resistance vessels of patients with non-insulin-dependent diabetes mellitus can be improved by administration of the antioxidant, vitamin C. These findings support the hypothesis that nitric oxide inactivation by oxygen-derived free radicals contributes to abnormal vascular reactivity in diabetes.

Arterial baroreflex regulation of blood pressure in patients with congestive heart failure

OBJECTIVES

This study was designed to determine whether arterial baroreflex control of blood pressure is altered in patients with congestive heart failure.

BACKGROUND

Arterial baroreceptor reflexes normally contribute to cardiovascular homeostasis by preserving blood pressure during changes in volume and posture.

METHODS

Arterial baroreceptor reflex function was studied in 18 patients with congestive heart failure and 18 age-matched healthy subjects. The arterial baroreceptor-blood pressure reflex was assessed by measuring the blood pressure response to perturbations in carotid sinus pressure. Carotid baroreceptors were stimulated by applying negative pressure to a custom neck chamber (-10, -20 and -30 mm Hg) and were unloaded by applying neck positive pressure (+10, +20 and +30 mm Hg).

RESULTS

Peak carotid baroreceptor-blood pressure reflex sensitivity was lower in patients with heart failure than in normal subjects (0.19 +/- 0.02 vs. 0.30 +/- 0.03 mm Hg/mm Hg, p < 0.05). During neck positive pressure, blood pressure increased less in the heart failure group than in the normal group. During neck suction, however, the decrease in blood pressure was similar in the two groups.

CONCLUSIONS

Patients with heart failure are less able than normal subjects to increase blood pressure during arterial baroreceptor unloading, but they can reduce blood pressure appropriately during baroreceptor stimulation. These observations suggest that the resting blood pressure position on the arterial baroreceptor stimulus-response curve, the operational point, is closer to the baroreceptor threshold in patients with heart failure than in normal subjects. As a result, reduced inhibitory signals from arterial baroreceptors most likely contribute to a heightened state of sympathetic activity and vasoconstriction in patients with congestive heart failure.

Impaired endothelium-dependent vasodilation in patients with insulin-dependent diabetes mellitus

BACKGROUND

Endothelium-dependent vasodilation is abnormal in experimental models of diabetes mellitus. We postulated that abnormalities of endothelial function are also present in patients with insulin-dependent diabetes mellitus and may contribute to the pathogenesis of vascular disease in these individuals.

METHODS AND RESULTS

Vascular reactivity was measured in the forearm resistance vessels of 15 patients with insulin-dependent diabetes mellitus and 16 age-matched normal subjects. No patient had hypertension or dyslipidemia. Each subject was pretreated with aspirin to inhibit endogenous production of prostanoids. Methacholine chloride (0.3 to 10 micrograms/min) was administered via the brachial artery to assess endothelium-dependent vasodilation. Sodium nitroprusside (0.3 to 10 micrograms/min) and verapamil (10 to 300 micrograms/min) were infused intra-arterially to assess endothelium-independent vasodilation; phenylephrine (0.3 to 3 micrograms/min) was administered to examine vasoconstrictor responsiveness. Forearm blood flow was determined by venous occlusion plethysmography, and dose-response curves were generated for each drug. Basal forearm blood flow in diabetic and normal subjects was comparable (2.6 +/- 0.2 versus 2.1 +/- 0.3 mL x 100 mL-1 x min-1, respectively; P = NS). The forearm vasodilative response to methacholine was less in diabetic than in normal subjects. At the highest dose of methacholine, the forearm blood flow increased 9.5 +/- 1.1 mL x 100 mL-1 x min-1 in diabetic subjects and 15.3 +/- 1.4 mL.100 mL-1 x min-1 in normal subjects (P < .01). The forearm blood flow responses to nitroprusside and verapamil and the forearm vasoconstrictor responses to phenylephrine were similar in diabetic and healthy subjects. In diabetic subjects, endothelium-dependent vasodilation correlated inversely with serum insulin concentration but not with glucose concentration, glycosylated hemoglobin, or duration of diabetes.

CONCLUSIONS

Endothelium-dependent vasodilation is abnormal in forearm resistance vessels of patients with insulin-dependent diabetes mellitus. This abnormality may be relevant to the high prevalence of vascular disease that occurs in these individuals.