ENDOGENOUS VASOPRESSIN MODULATES THE BAROREFLEX SENSITIVITY IN RATS

The effect of endogenous vasopressin on the baroreceptor reflex has been examined by comparing baroreflex function in Brattleboro rats with hereditary hypothalamic diabetes insipidus (DI rat) with that in Long-Evans rats (LE rat). Baroreflex function was assessed in conscious unrestrained rats during increases in blood pressure with phenylephrine. The slope of the baroreflex function line in LE rats [(19.0, s.e.m. = 1.4) X 10(-4), n = 34] was significantly steeper than that in DI rats [(6.9, s.e.m. = 0.6) X 10(-4), n = 44, P less than 0.0001]. A subpressor infusion of arginine8-vasopressin (2 ng/kg per min for 2 h i.v.) and an equidose of DDAVP caused bradycardia and increased the baroreflex function slope significantly. Acute volume expansion in DI rat did not change the baroreflex sensitivity. A specific vasopressin vascular receptor antagonist, d(Ch2)5Tyr(Me)AVP, did not alter the baroreflex sensitivity in LE rats. These results suggest that endogenous vasopressin is an important physiological regulator of the baroreflex sensitivity in normal rats.