Steroid Induction of Phenylethanolamine-N-methyl Transferase

Unilateral explants of rat adrenal medullas grown in the anterior chamber of the eye contained very low phenylethanolamine-Nmethyl transferase (PNMT) activity. When animals were treated with dexamethasone for 7 days, PNMT activity rose more than 10-fold. These findings suggest that the increase in PNMT activity produced by glucocorticoids does not require an intact adrenal innervation. (Endocrinology 86: 1466, 1970) THE ABILITY of the adrenal medulla to secrete epinephrine depends upon both neural and hormonal factors. The secretory process, per se, is under direct neural control: it is triggered by impulses from sympathetic cholinergic nerves that terminate adjacent to the adrenal chromaffin cells (1-3). In contrast, the chemical composition of the secreted material is regulated by hormonal inputs: the ratio of epinephrine to norepinephrine in adrenal venous blood is variable and depends on the concentration of glucocorticoids perfusing the chromaffin cells (4). The conversion of norepinephrine to epinephrine is catalyzed by phenylethanolamine-N-methyl transferase (PNMT) (5, 6), an enzyme induced by natural Received December 15, 1969. or synthetic glucocorticoids (7-9). The concentrations of glucocorticoids needed to maintain optimal PNMT activity are high (9); these concentrations are, however, available to the medulla by virtue of a portal vascular system (10) that allows adrenocortical venous blood to perfuse the medulla without prior dilution. If the preferential delivery of glucocorticoids to the medulla is interrupted [e.g., by removal of the pituitary gland (7) or by administration of low doses of dexamethasone (11), which suppress the secretion of endogenous glucocorticoids], PNMT activity declines, as do the ratios of epinephrine to norepinephrine in the adrenal gland (9) and in adrenal venous blood (4). Surgical denervation of the adrenal medulla has been reported to cause few if any characteristic changes in the histology of the Iqp~~~~~~~~~~~~ nX~~~~~~~~~~-I 1