EPINEPHRINE AND NOREPINEPHRINE ELEVATE 5'-MONODEIODINASE ACTIVITY IN RAINBOW-TROUT LIVER SLICES

The 5'-monodeiodinase (5'-MDA) activity was measured in liver slices t hat were incubated for 3 hours with epinephrine (E) or norepinephrine (NE) in order to examine the influence of these catecholamine hormones on the regulation of hepatic monodeiodination of thyroxine (T-4) in r ainbow trout. Both E and NE induced a dose-dependent increase in 5'-MD A activity and in addition, E stimulated the release of T-3 into the m edium. In liver slices taken from trout that had been treated with the beta-adrenoceptor inhibitor propranolol, the response to both E and N E was attenuated. The findings provide evidence of an action of these catecholamine hormones on the peripheral regulation of T-3 production, and suggest that the control operates via the beta-adrenoceptors.