ACTH INCREASES ADRENAL-MEDULLARY PNMT ACTIVITY IN NEONATAL RATS

Levels of plasma corticosterone and the activities of adrenomedullary dopamine-.beta.-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) were measured in the 7-day-old rat following the administration of adrenocorticotropic hormone (ACTH) for 7 consecutive days beginning with day 1. ACTH led significant adrenal hypertrophy and a concomitant elevation (10 to 15 fold) of plasma corticosterone concentration. Whereas DBH activity remained unchanged, adrenal PNMT activity was increased significantly following ACTH-induced elevation of plasma corticosterone levels. These results indicate that the pituitary-adrenocortical-adrenomedullary axis is functional in the neonatal rat. Furthermore, since the transsynaptic control mechanisms are known to be non-functional or immature in the 7-day-old rat, our data suggest that neontal rat adrenal catecholamine biosynthesis may be largely controlled by the pituitary-adrenocortical axis via glucocorticoids.