MECHANISM OF EPINEPHRINE INHIBITION OF THE MILK EJECTING RESPONSE TO OXYTOCIN

¹ Department of Biochemistry, Cornell University Medical College, New York, N. Y.

The mechanism of epinephrine inhibition of milk ejection was studied in reserpinized lactating rabbits. Epinephrine and norepinephrine inhibited the milk ejecting response to oxytocin. Isoproterenol also had strong inhibitory activity whereas angiotensin had none when comparable pressor doses were injected. Alpha- and -adrenergic blockade abolished the vascular responses to epinephrine but had no effect on its milk ejection inhibitory activity. The inhibitory activity of epinephrine was also demonstrated in the isolated mammary strip. These findings indicate that the milk ejection inhibitory activity of epinephrine is an intrinsic activity of the hormone acting directly on the mammary tissue and is not the result of its vasoconstrictor activity preventing oxytocin from reaching the mammary gland as has hitherto been supposed.

Studies on other sympathomimetic amines suggest that the catechol nucleus is important to the milk ejection inhibitory activity of these amines. The N-alkyl group also influences this inhibitory activity.