1 h after a single dose of 2 mg prazosin tachycardia and a decrease in blood pressure developed. Renin activity in the peripheral plasma (PRA) increased from 1.04 ± 0.15 to 2.64 ± 0.20 ng AgT/ml/h. A 3-day treatment with 2 mg t.i.d. prazosin of 11 patients caused no further ...