Acute action of guanfacine on peripheral circulation in hypertensive patients: measurements of arterial flow of the calf and of the forefoot, of venous capacity of the calf, of the blood pressure and of the heart rate.

1. The acute action of an intravenous infusion (5 min) of guanfacine in doses of 0.01, 0.02 and 0.04 mg/kg on peripheral circulation was studied in five hypoertensive patients and compared with a placebo in a randomized study. The observations were combined for 2 h after drug administration. 2. Two phases of drug action were seen during and immediately after the administration of guanfacine; a dose-dependent decrease in blood flow mainly of the forefoot but also in the calf was combined with an increase in systolic and diastolic blood pressures and a decrease in heart rate. Peripheral resistance was increased in this phase. Later, an increase in blood flow to the foot combined with a tendency towards a decrease in blood pressure were observed. 3. These preliminary results show that this second phase of action of guanfacine is dependent on the dose given.