Vasopressin is not involved in the catecholamine-induced release of ACTH, alpha-MSH and beta-endorphin from the rat pituitary gland

The effect of catecholamines on plasma levels of immunoreactive ACTH (ACTHi), alpha-MSH (alpha-MSHi), beta-endorphin (beta-ENDi), arginine-vasopressin (AVPi) and of corticosterone (B) was studied in female rats. Intravenous infusion of the specific beta-adrenoceptor-stimulating agent l-isoproterenol in Wistar rats under pentobarbital anesthesia resulted in a dose-dependent (dose range: 10-100 ng/kg . min) increase in plasma B. At higher concentrations, l-isoproterenol also caused a dose-dependent increase in plasma AVPi (dose range: 100-1,000 ng/kg . min). In addition to isoproterenol, also intravenous infusion of l-epinephrine caused a dose-dependent increase of plasma B (dose range: 100-1,000 ng/kg . min), whereas l-epinephrine was without effect on plasma AVPi, even at the highest dose tested (1,000 ng/kg . min). The effect of l-epinephrine or l-isoproterenol on plasma B was associated with a parallel and dose-related increase in plasma ACTHi, beta-ENDi and alpha-MSHi. The increase of plasma ACTHi, B and beta-ENDi in response to l-isoproterenol (300 ng/kg . min) was identical in Wistar, Long Evans and Brattleboro rats (Long Evans rats with a hereditary lack of vasopressin). Also the responses to l-epinephrine (1,000 ng/kg . min) were identical in Wistar and Brattleboro rats. We conclude that vasopressin does not mediate the catecholamine-induced release of ACTH, beta-endorphin and alpha-MSH.