Influence of corticosterone on the stress-induced elevation of phenylethanolamine- N-methyl transferase activity in the avian adrenal

Abstract

The mechanism of adrenal phenylethanolamine- N-methyl transferase (PNMT) elevation occurring in the avian stress response was evaluated in 8- to 9-wk-old White Leghorn cockerels. The nonspecific stressor used in this study was a single 3-hr period of immobilization. The following physiological parameters were measured: (1) plasma and adrenal concentrations of epinephrine (E) and norepinephrine (NE); (2) plasma concentration of corticosterone (B); and (3) adrenal PNMT activity. It was found that if an inhibitor of B biosynthesis (Metopirone) was administered prior to the restraint period, the elevation in adrenal PNMT activity normally occurring with immobilization was prevented. The Metopirone-treated group also showed significantly smaller adrenal and plasma levels of E after restraint as compared to the non-drug-treated group. In contrast there was no significant difference between the restrained control group and the restrained group given Metopirone in their plasma and adrenal levels of NE. Puromycin given prior to immobilization was also effective in preventing the increased PNMT activity seen with immobilization. The administration of a large dose of B did not alter the blocking action of puromycin on PNMT elevation. The plasma concentrations of E and NE were also significantly smaller in the restrained group given puromycin as compared to the non-drug-treated restrained group. It is concluded that B does cause an increase in PNMT activity during the avian stress response and that this increase in activity provides a means for replenishing the adrenal with E under the condition of stress. The regulation of PNMT activity by B appears to be by enzyme induction.