Inhibitory Effect of L-Dihydroxyphenylalanine on the Adrenal Venous 17-Hydroxycorticosteroid Response to Surgical Stress in Dogs

Abstract

The effect of intravenous L-dihydroxyphenylalanine (L-dopa) on the adrenal venous 17-hydroxycorticosteroid (17OHCS) output in response to laparotomy and intestinal manipulation was studied in pentobarbital-anesthetized dogs. L-Dopa, 50 mg/kg but not 10 nag/kg, markedly decreased the 17OHCS response to surgical stress. The catecholamines, norepinephrine and dopamine, administered intravenously, did not have this inhibitory effect on 17OHCS output. The effect of L-dopa in inhibiting the 17OHCS response to stress was not dependent on the increase in blood pressure that it produced, since prior treatment of dogs with the α-adrenergic blocking agent, phenoxybenzamine, prevented the pressor response to L-dopa without altering the effect on 17OHCS output. The minimum effective dose of L-dopa that inhibited the 17OHCS response to stress was decreased by the monoamine oxidase inhibitor, pargyline, and increased by the catecholamine synthesis inhibitor, α-methyl-ptyrosine. These data support the hypothesis of a central adrenergic neural system which inhibits ACTH secretion in dogs. (Endocrinology88: 1404, 1971)