Effects of insulin and glucagon on plasma glucose levels and glycogen content in organs of the freshwater teleost Pimelodus maculatus.

Mammalian insulin (350 IU/kg) and glucagon (2.5 mg/kg) were injected intraperitoneally into Pimelodus maculatus, a South American teleost. Extent of carbohydrate regulation was estimated through determination of plasma glucose levels, liver-somatic index, and liver and muscle glycogen contents. The effects of insulin administration, examined 6, 12, 24, 48, and 72 hr after injection, were manifested as a depletion of liver glycogen content after 12 hr and severe decrease in plasma glucose content after 24 hr; insulin had no effect on muscle glycogen or liver-somatic index. The effects of glucagon administration, examined 5, 15, 30, 90, and 360 min after injection, were a small increase in liver glycogen content after 15 min, and hyperglycemia, apparent after 30 min. Glucagon did not affect muscle glycogen or liver-somatic index. Control animals were injected intraperitoneally with saline solution. These results suggest that insulin and glucagon regulate the carbohydrate metabolism of P. maculatus by hormonal mechanisms similar to those operating in other teleost species and in mammals.