Regulation of the adrenomedullary catecholaminergic system after mild, acute stress.

The time course of regulation of rat adrenomedullary phenylethanolamine N-methyltransferase (PNMT) and tyrosine hydroxylase (TH) activity was studied after a single episode of 20-min restraint stress. Significant increases in PNMT and TH activity were observed 18 h after the beginning of the stress. The time course of acute stress-induced regulation of PNMT and TH was examined for the influence of neural and hormonal input. Unilateral denervation was performed, and the animals were exposed to a single episode of restraint. PNMT activity increased similarly in both the innervated and denervated adrenals, with a significant increase observed at 36 h after the stress. TH activity was similar in both denervated and innervated adrenals, with a significant increase observed at 24 and 36 h after stress. Finally, suppression of endogenous corticosterone with dexamethasone delayed the stress-induced increase in activity of PNMT but not TH. The present study indicates that increases in catecholamine biosynthetic enzymes can be observed after a single episode of mild, acute stress. In addition, glucocorticoids appear to be important in the time course of the stress-induced increase in PNMT but not TH activity, whereas neural input does not seem to affect the time course of these increases.