EFFECTS OF INSULIN IN TOADFISH OPSANUS TAU

Intravenous administration of glucose (0.5 g/kg) to toadfish (Opsanus tau) produced a rise in blood glucose concentration with a return to normal levels by 6 hours. Insulin caused a reduction in glucose concentration in fish caught in the fall but not in the early summer. Fish force-fed protein for 4 days had a significantly higher level of serum immunoreactive insulin than did fasted controls, but there was no change in glucose concentration. Insulin accelerated disappearance of U-14C glucose from the blood and increased incorporation of glucose carbon label into muscle protein and glycogen. In vitro experiments also showed that insulin stimulated labeled glucose uptake into muscle glycogen. Experiments with glycine-2-14C revealed that insulin accelerated glycine incorporation into skeletal muscle protein and lipid. These findings suggest that one of the prime effects of insulin is on the incorporation of glucose and amino acids into skeletal muscle, glycogen, and protein, and that these fish have a good homeostatic mechanism for the regulation of blood glucose concentration which appears to be relatively independent of insulin levels. © 1968.