Carbohydrate Oxidation in Hypophysectomized Rats

Abstract

It was noted that rats hypophysectomized∗ for 6 to 8 weeks, with metabolic rates 70% of those of normal controls (as determined gravimetrically by the Haldane method), frequently showed high respiratory quotients (R.Q.) after a fasting period of 24 hours. Values as high as 0.78 to 0.81 were sometimes observed, the average of a series of 19 observations being 0.75, while the average of 19 controls was 0.72. If the hypophysectomized rats were fasted longer than 30 hours, the R.Q. usually dropped to 0.73, though in a few instances it remained high for nearly 40 hours. Changes in the acid-base equilibrium were apparently not responsible for the high R.Q., as shown by determinations of the CO₂ content of the blood. Glycogen determinations after a 24-hour fast showed that the hypophysectomized animals contained considerably less muscle and liver glycogen than did normal controls. Hypoglycemia was always present, the blood sugar being around 50 mg. %.

These findings suggested that the regulatory mechanism which leads to the preservation of glycogen during fasting is disturbed after hypophysectomy. The low glycogen reserves and the tendency to hypoglycemia in hypophysectomized animals might be due, among other factors, to the removal of an inhibitory influence on carbohydrate oxidation. In order to test this assumption, a standard amount of glucose (500 mg. per 100 gm. of body weight) was fed to normal and hypophysectomized rats after a fasting period of 24 hours, the aim being to determine (a) how much glucose was oxidized in the first few hours during the period of active absorption and (b) what length of time was required for the complete disposal of the ingested sugar by oxidation.