The action of insulin in normal young rabbits

Abstract

Groups of litter-mate rabbits, 6-10 weeks old, were starved for 24 hrs. They were killed by a blow on the head, blood was collected from the heart (for sugar determination according to the MacLean method), the liver was excised, the hind legs skinned and the gastrocnemii removed for glycogen determinations by means of the Pfluger method. The group receiving insulin was given 0.5 units once or repeatedly. In many instances convulsions occurred. The rabbits were killed one to several hours after the first injection or died in convulsions. The average liver glycogen content of 12 controls was 50 mgm., the individual variability being comparatively insignificant. In 12 in-sulinized rabbits, the average liver glycogen content was 237 mgm.; in many of these animals the blood sugar concentration was zero. The muscle glycogen in controls and insulinized rabbits showed marked individual variability. Epinephrine did not prevent the accumulation of liver glycogen after insulin injection though it relieved the hypoglycemia. During ether narcosis insulin did not bring about the usual increase of liver glycogen. Strychnine in convulsive doses also prevented the accumulation of glycogen in the liver, which otherwise took place after insulin injection. In 2 non-fasting rabbits the liver glycogen after insulin was once higher and once lower than in 2 controls. In one of these rabbits, in which convulsions intervened, the liver contained 9.9% of glycogen. The conclusion is reached that the fasting animal keeps up its blood sugar by absorption from the gut and by gluconeogenesis from protein and fat. Insulin under these conditions blocks the release of carbohydrates from the liver, but offers no obstruction to absorption and gluconeogenesis. The result is an increase in liver glycogen.