VASOPRESSIN DILATES THE RAT CAROTID-ARTERY BY STIMULATING V1 RECEPTORS

The acute effects of various vasopressor agents on the diameter of the common carotid artery were studied in halothane-anesthetized normoten sive rats. The animals were infused intravenously for 60 min with equi pressor doses of angiotensin II(10 ng/min), the alpha(1)-stimulant met hoxamine (5 mu g/min), lysine vasopressin (5 mU/min), or vehicle. The arterial diameter was measured by using a high-resolution ultra-sonic echo-tracking device. The three vasoconstrictors increased the carotid artery diameter, but this effect was significantly more pronounced wi th lysine vasopressin. Even a nonpressor dose of lysine vasopressin (1 mU/min) caused a significant increase in the arterial diameter. The l ysine vasopressin-induced vasodilatation could be prevented by the adm inistration of d(CH2)(5)Tyr(Me)AVP (10 mu g, i.v.), a selective V1-vas opressinergic receptor antagonist. These data therefore suggest that a short-term increase in blood pressure induces in rats a distention of the carotid artery. The increase in arterial diameter seems to involv e an active mechanism with lysine vasopressin caused by the stimulatio n of V1-vasopressinergic receptors.