Influence of Phentolamine on the centrally induced Renal effects of Norepinephrine and Dopamine in the Rabbit

Ko, Kwang Hoo

Abstract

It has recently been reported that both norepinephrine and dopamine elicit antidiuresis when given intracerebroventricularly. But no inference has been made as to their mechanisms. As dopamine is the immediate precursor of norepinephrine in the biosynthesis of catecholamine, it might be possible that dopamine might act indirectly through increased level of norepinephrine in the brain tissue. To certify whether the dopamine-induced antidiuresis is related to norepinephrine, the influence of phentolamine, a specific alpha-adrenergic blocking agent, on the centrally induced antidiuresis of both norepinephrine and dopamine was investigated in this study. Norepinephrine and dopamine given intraventricularly elicited maximal antidiuresis in doses of 10ug and 500ug, respectively. Phentolamine, administered intravenously in dose of 2mg/kg, abolished the renal effect of norepinephrine given intraventricularly, but did not influence the antidiuresis induced by dopamine. It is suggested that both norepinephrine and dopamine produce antidiuresis when given intracerebroventricularly but their actions are mediated by different mechanisms, and that norepinephrine does not participate in the renal action of dopamine.