Mechanism for the cardiovascular action of intracerebroventricularly administered vasoactive intestinal polypeptide in rats.

It was investigated whether the secretion of epinephrine, norepinephrine, and arginine vasopressin from the adrenal medulla, sympathetic nerve endings, and posterior pituitary gland, respectively, was involved in the mediation of the pressor effect of intracerebroventricular (icv) administration of vasoactive intestinal polypeptide (VIP) in anesthetized rats. Icv administration of 1 microgram VIP increased mean blood pressure by 21% and heart rate by 17% in Wistar rats although the lesser dose was effective only for increasing heart rate. Simultaneously with the change in blood pressure and heart rate, the concentrations of plasma epinephrine and norepinephrine rose 4 and 10 min after VIP administration. After adrenalectomy, the action of VIP on mean blood pressure or heart rate was unchanged or partially reduced, respectively. Although the cardiovascular action of VIP was observed in control Long-Evans rats as well as in Brattleboro rats homozygous or heterozygous for diabetes insipidus, which hereditarily lacked vasopressin completely or partially, the increase in mean blood pressure after icv administration of VIP was more marked in homozygous than heterozygous rats or Long-Evans rats. These results suggest that the cardiovascular action of centrally administered VIP is mediated by increased sympathetic nerve outflows including stimulation of adrenal epinephrine secretion and is enhanced by the chronic absence of vasopressin secretion from the posterior pituitary gland.