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To investigate whether differences exist in peripheral alpha 2-adrenoceptors between normotensive and hypertensive subjects, we determined platelet alpha 2-adrenoceptor density in 10 (7 males) untreated essential hypertensives (mean age of 51.1 years, range of 44-59 years) and in 10 age- and sex-matched normotensive controls. Moreover, in hypertensive patients, we examined the relationship between receptor density and cardiovascular reactivity to mental arithmetic, static handgrip, and bicycle exercise, to verify the hypothesis that alpha 2-adrenoceptors might play a role in modulation of hemodynamic response to sympathetic stimuli. alpha 2-Adrenoceptor density, as calculated by binding of [3H]yohimbine to platelets, was significantly higher in essential hypertensives (314.8 +/- 38.7 fmol/mg) than in normotensive subjects (213.6 +/- 34.7 fmol/mg) (p less than 0.05), whereas receptor affinity was similar in both groups (4.0 +/- 0.5 nM hypertensives, 4.3 +/- 0.5 nM normotensives; p greater than 0.05). Mental arithmetic increased mean arterial pressure (MAP) by 21.5% from basal values and heart rate (HR) by 13.2%. During isometric exercise, MAP increased by 38.1% and HR by 24.7%, while during bicycle ergometry, mean increases in MAP and HR from baseline were of 27.2 and 54.3%, respectively. No correlation was found between platelet alpha 2-adrenoceptor density and percent changes in MAP induced by all tests, or between adrenoceptors and absolute basal and peak MAP values. Our findings suggest that in hypertensive patients, peripheral alpha 2-adrenoceptors are increased with respect to matched normotensives, but these receptors seem not to be involved in the modulation of cardiovascular adaptation to enhanced sympathetic activity.

The antihypertensive effect of a drug should be present not only at rest, but also during usual daily activities and pressor stimuli. In our study, we tested the impact of a new formulation of sustained-release (SR) verapamil (240-mg tablets), given once or twice daily, on 24-h ambulatory blood pressure (BP) and on pressor response to isometric exercise (handgrip). Fourteen mildly to moderately essential hypertensive patients were included in a single-blind placebo-controlled trial. The mean titrated dose of verapamil required to normalize office BP was 430 +/- 28 mg/day. Mean 24-h waking (7 a.m.-11 p.m.) and sleeping (11 p.m.-7 a.m.) blood pressures were significantly lower after verapamil than after placebo. The absolute levels of BP achieved at peak of handgrip (30% of maximal voluntary contraction for 3 min) were significantly reduced by verapamil with respect to placebo. However, due to the lower starting values, the pressor increment to the isometric work was not significantly modified by the active treatment. In conclusion, SR verapamil seems to provide a blood pressure lowering effect during all times of the day. It attenuates the surges in BP associated with handgrip exercise.