Effect of treatment with chlorthalidone and atenolol on response to dilator agents in the forearm resistance vessels of men with primary hypertension.

Abstract

1 The forearm resistance vessels of men with primary hypertension respond to verapamil with a greater than normal dilatation relative to that induced by sodium nitroprusside. 2 We have examined the effect on this functional abnormality of treatment with chlorthalidone (50 mg daily in 16 patients) and atenolol (100 mg daily in eight patients and 200 mg daily in two).3 The responsiveness of the forearm resistance vessels to local intra-arterial infusion of verapamil and sodium nitroprusside was assessed before treatment and again after a minimum of 1 month ofdrug therapy. Forearm blood flow was measured by venous occlusion plethysmography. 4 Chlorthalidone induced significant reductions in calculated mean arterial pressure, which fell from 135 ± 4 to 117 + 4 mm Hg, and the dilator response to verapamil at 5 ,ug/min, which was reduced from 2.4 ± 0.2 to 1.5 ± 0.2 ml min-' 100 ml-' forearm; the response to sodium nitroprusside at 3.2 ,ug/min was not significantly changed. 5 Atenolol induced significant reductions in mean arterial pressure, which fell from 134 + 6 to 123 ± 6 mm Hg, heart rate which fell from 72 + 3 to 55 + 2 beats/min, and response to verapamil at 5 ,ug/min which fell from 2.7 + 0.2 to 2.1 ± 0.2 ml min-I 100 ml-' forearm; the response to sodium nitroprusside was not significantly changed. 6 Both drugs caused reversion towards normal of the relative enhancement of responsiveness to verapamil that was present before treatment. Normalization of this aspect of resistance vessel function may be one component of the mechanism by which both diuretics and 18-adrenoceptor antagonists exert their antihypertensive effect.