Effect of adrenalectomy on glucose homeostasis in rats fed a high-protein, carbohydrate-free diet.

1. The effect of adrenalectomy on the adjustments of carbohydrate metabolism to fasting was studied in rats fed a high-protein, carbohydrate-free (HP) diet. 2. Fasting for 24 h induced a 20% decrease of blood glucose levels in intact rats on the balanced, control (C) diet, but did not affect the blood glucose levels of rats adapted to the HP diet. After adrenalectomy, HP rats lost their capacity to maintain constant blood glucose levels during fasting, but the reduction in blood glucose (30% after 24 h) took longer to appear and was 50% smaller than in adrenalectomized C-rats. 3. Intact rats on the control diet responded to fasting with increased in vitro hepatic gluconeogenic capacity as well as increased phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase activities. Adrenalectomized C-rats also responded to fasting with increased gluconeogenesis and PEPCK activity. In contrast, for both intact and adrenalectomized HP-fed rats, liver gluconeogenesis and PEPCK activity, which were already high in the fed state, did not change or even decreased slightly after fasting. 4. After food restriction, the rates of glucose replacement by adrenalectomized rats on the control diet were higher than those of intact animals on the same diet. This effect was not observed in HP-fed rats, in which the rates of glucose replacement were even slightly lower in adrenalectomized than in intact animals. 5. These data suggest that the mechanism of fasting-induced hypoglycemia after adrenal removal is different for HP and control rats.(ABSTRACT TRUNCATED AT 250 WORDS)