Pancreatic Hormones and Plasma Glucose: Regulation Mechanisms in the Goose under Physiological Conditions - III. Inhibitory Effect of Insulin on Glucagon Secretion

Abstract

Previous studies had pointed to 1) glucose-glucagon and 2) glucose-insulin feedback mechanisms operating under physiological variations of plasma glucose concentration. The present series of experiments was designed to see if insulin exerted a direct effect on glucagon secretion.

Small doses of insulin, at 3 different concentrations, were infused or injected IV into 47 fasted geese and peripheral blood samples taken shortly afterwards. Insulin and GLI were measured using radioimmunological techniques. The non-specific glucagon antibody used measured mainly pancreatic glucagon in the fasting Goose. While an infusion of saline over one hour was ineffective, 2.5 mU/kg of insulin over 10 minutes provoked a significant drop in GLI at the 6th minute. A drop in glycaemia was observed only later and explained the return of the glucagonaemia to normal.

With 5 mU/kg/min over 10 minutes, this phenomenon was exaggerated. The inhibitory effect was still evident at 10 minutes, despite a glycaemia significantly lower than at zero time.

A rapid injection of 200 mU insulin gave similar results, but after 10 minutes the resulting hypoglycemia restored the GLI above basal level and masked the inhibitory effect of insulin.

It was concluded that insulin inhibits glucagon secretion in the Goose, this effect being secondarily masked by the hypoglycemia.

Key words

Goose - Physiological Conditions - Inhibitory Effect - Insulin - Glucagon