Prazosin produces a sustained and reflex-mediated increase in renal sympathetic nerve activity in anesthetized dogs

Prazosin (1 mg/kg i.v.) produced a decrease in blood pressure associated with an increase in renal sympathetic nerve activity in anesthetized dogs. The sympathetic baroreflex curve was shifted to the left. Prazosin (10 micrograms/kg into the vertebral artery) did not change the blood pressure but increased renal sympathetic discharges. The baroreflex curve was not altered. Prazosin (100 micrograms/kg into the vertebral artery) induced a decrease in blood pressure and an increase in sympathetic discharges. Prazosin (1 mg/kg i.v. or 100 micrograms/kg i.c.) induced a fall in blood pressure without any change in sympathetic nerve activity in barodenervated dogs. Restoration of the resting blood pressure by angiotensin II infusion (10-20 ng/kg per min) restored the baroreflex curve in anesthetized dogs given prazosin (1 mg/kg i.v.) to close to the initial position. Prazosin, (1 mg/kg i.v.) did not change the sympathoinhibitory effect of clonidine (injected into the vertebral artery) and the reversal effect of piperoxan in barodenervated dogs. In conclusion, prazosin reduces blood pressure by blockade of peripheral alpha 1-adrenoceptors. The shift to the left of the sympathetic baroreflex curve is due to the hypotensive effect of prazosin. No evidence was found for a central sympathoinhibitory effect of prazosin.