Effect of Insulin on Partially Hypophysectomized Rats

Abstract

Although much work has been done on the relation of the pituitary gland to the glucose regulatory system, the exact nature of the reaction is not yet clear. Early experiments showed an increased insulin sensitivity in hypophysectomized animals. 1 , 9 , 5 This has been assumed to indicate the complete ablation of the hypophysis. 7 Posterior lobe extracts have been shown to diminish or abolish this sensitivity and to neutralize the toxic effect of hypoglycemia. 1 , 8 Some workers have shown that the nature of the antagonism of posterior lobe extract to insulin-glucose mechanism is related to the peripheral utilization of blood glucose, 2 while others have sought to explain this antagonism, existing in over-activity of the pituitary, by changes in general carbohydrate metabolism within the animal organism. 6

Sex hormone extract from the anterior lobe of the hypophysis has produced an increased blood glucose, while the growth hormone has been shown to produce little effect. 3 Other investigators could demonstrate little or no effect of anterior lobe products on this insulin-glucose mechanism. 8

Hypophysectomy has been believed to disturb the regulatory mechanism which tends to preserve glycogen during fasting. 4 An accessory pancreatic factor has been postulated, since the complete ablation of the hypophysis in depancreatized dogs enables them to utilize carbohydrate. 8 The magnitude of fall in blood glucose values after insulin has been shown to be increased from 14% to 35 a/o by complete hypophysectomy in monkeys, while incomplete hypophysectomy produced an almost insignificant change from normal. 12

Experimental investigation in glandular physiology has been done largely on completely hypophysectomized animals. Therefore, it seemed desirable in this investigation to study the nature of insulin sensitivity of albino rats partially hypophysectomized.