THE EFFECTS OF INSULIN AND SOMATOTROPHIN ON THE GROWTH OF HYPOPHYSECTOMIZED RATS

Abstract

Growth induced by exogenous insulin in hypophysectomized rats on an unrestricted diet is similar to that stimulated by somatotrophin. Both hormones promote skeletal growth and produce an increase in weight that is due to an increase in total body protein, fat, and water. However, insulin-treated animals consume more food, produce more fat, retain less water, and exhibit less skeletal growth than comparable rats treated with somatotrophin. Insulin and somatotrophin promote the synthesis of similar amounts of protein under our experimental conditions. Insulin-induced growth is enhanced and the disproportionate increase in fat is prevented by the simultaneous administration of somatotrophin. Insulin cannot stimulate protein anabolism in hypophysectomized rats restricted to the amount of food consumed prior to treatment. When the insulin-treated animals are allowed to consume glucose in addition to their basal ration there is a marked increase in the amount of ingested nitrogen retained. A comparable reduction in nitrogen excretion cannot be achieved when the carbohydrate supplement is replaced by fat. The results also indicate that under the experimental conditions described, the protein sparing action of glucose is dependent upon an adequate supply of insulin.