Physiologic effects of prazosin HCl: consequences of diuretic combination therapy.

The physiologic action of prazosin in man was studied in 23 patients including 10 treated with prazosin plus polythiazide. Responders to prazosin alone (blood pressure fell greater than 10 mm Hg) had a decrease in peripheral resistance (p less than 0.02) and no significant change in plasma volume, while nonresponders' plasma volume rose significantly (p less than 0.02). 10 patients treated with prazosin and polythiazide (blood pressure not normalized on prazosin alone) were analyzed at baseline (Rx 0), after prazosin (Rx 1), and after prazosin plus polythiazide (Rx 2). Mean supine blood pressure fell from 184/118 +/- 8/5 (SE) mm Hg at Rx 0 to 161/106 +/- 7/4 mm Hg at Rx 1 (p less than 0.005) and 129/89 +/- 4/4 mm Hg at Rx 2 (p less than 0.001). Supine renin increased in each group, but the increase with prazosin alone was not significant. Stimulated renin activity increased significantly after Rx 2 (p less than 0.0025). Cardiac output fell, plasma volume returned to baseline values, and peripheral resistance fell by 467 dyn s/cm-5 during thiazide treatment (p less than 0.025).