Effect of chlorothiazide on response of renal vascular bed to vasoactive substances.

• It seems fairly well established that chlorothiazide reduces the rise in arterial pressure produced by intravenously injected Z-epinephrine and levarterenol in the normotensive animal and in the normotensive and hypertensive human. Chlorothiazide has also been shown to increase the effectiveness of a variety of antihypertensive agents and the reduction of arterial blood pressure in the sympathectoinized hypertensive patient. However, there is no information which indicates whether the attenuation of the cateeholamine response is mediated through an effect upon cardiac output or through an effect upon blood vessels. For this reason, the acute effect of chlorotliiazide upon the response of the renal vascular bed to locally injected, naturally occurring vasoactive agents was studied in a preparation which eliminated the factor of change in blood flow. In addition, the study permitted an examination of the effect of chlorothiazide per se upon renal vascular resistance.