Age-related changes in the response of hepatic succinic dehydrogenase activity to thyroxine and thiourea in lizards.

Intraperitoneal injection of thyroxine (T4; 1 microgram/g body weight on alternate days, seven doses) to male garden lizards of three different age groups caused a stimulation of hepatic succinic dehydrogenase activity, the degree of response being higher in the old (63%) than in middle-aged (39%) and young (31%). Percent inhibition of enzyme activity following thiourea treatment (0.05 mg/g body weight on alternate days, three doses) was higher in middle-aged lizards (24%) than in young (10%) and old (12%) ones.