Abstract
1. After administration of reserpine to rats, the tyrosine hydroxylase (TH) and phenylethanolamine-N-methyl transferase (PNMT) activity in their adrenal glands was found to be increased under in vitro conditions.2. The increase in TH activity occurred at 12-18 h after reserpine whereas the PNMT activity increased at 30 hours. Unlike the TH, the increase in PNMT activity did not appear to be neuronally mediated since ganglion blockade by chlorisondamine failed to antagonize the reserpine-induced increase in PNMT activity. The increase in PNMT activity may be a response to increased utilization of catecholamines.3. Hypophysectomy resulted in a diminution of the activities of both enzymes; the activity of TH, but not of PNMT, could be partially restored by reserpine. ACTH restored the activities of both enzymes almost to normal.4. The differential effect of reserpine suggests that the activities of these two enzymes are controlled by different mechanisms.