Effect of Hypophysectomy and Insulin on Lipogenesis in Cockerels

Abstract

Hypophysectomy increases hepatic lipogenesis in cockerels. In an attempt to find the possible hormonal mechanism for this we have examined the effects of hypophysectomy, insulin and pituitary homogenates on hepatic lipogenesis.

Insulin (5 U/kg) injected intravenously, simultaneously with glucose-¹⁴C tracer, increased the amount of ¹⁴C found in liver lipids at 30 min after the injection. Similarly, insulin injected 5 min before killing, increased the incorporation of glucose-¹⁴C and acetate-¹⁴C by liver slices during a 30 min incubation. Hypophysectomy increased lipogenesis within 24 hours. The effect of insulin was most pronounced in hypophysectomized cockerels. The activity of the lipogenic enzyme, acetyl CoA carboxylase was similarly affected.

A homogenate of chicken pituitaries added to the medium reduced lipid synthesis from glucose-¹⁴C by liver slices. This effect was larger in liver slices in which lipogenesis had been stimulated by insulin.

The increased rate of hepatic lipogenesis in hypophysectomized cockerels may be caused partly by increased hepatic sensitivity to the lipogenic action of insulin or by the removal of a direct inhibition by pituitary hormones.

Key words

Hypophysectomy - Lipogenesis - Fatty Acids - Acetyl CoA Carboxylase - Insulin - Pituitary Homogenate