Possible intervention of insulin, cyclic AMP, and glucocorticoids in protein-sparing action of dietary carbohydrate in rats.

The present study was carried out to examine the possible intervention of some hormones in the "protein-sparing/actions of dietary carbohydrate and fat. Administration of either a carbohydrate meal or a fat meal to fasted rats caused a reduction in the urinary output of urea and total nitrogen with a concomitant decrease in rate of urogenesis in liver. as well as the activities of some amino acid-catabolizing enzymes in liver. The sparing action of carbohydrate but not that of fat was abolished in alloxan-diabetic rats. Feeding rats a carbohydrate meal caused a marked reduction in the amount of cyclic AMP in liver. The change was coincident with a reduction in the level of plasma urea and the urinary output of urea and total nitorgen. Administration of dibutyryl cyclic AMP abolished the carbohydrate-induced depression of urinary output of urea and total nitrogen as well as partially the activity of serine dehydratase in liver. Feeding a carbohydrate meal resulted in a significant reduction in the level of corticosterone in plasma. However, the possible intervention of glucocorticoids in the protein-sparing action of carbohydrate was ruled out inasmuch as the action of carbohydrate was also observed in the adrenalectomized rats. The overall results suggest that the protein-sparing action of dietary carbohydrate may be exerted in a different fashion from that of fat, that is, through depression of cyclic AMP in liver and thus the reduction of the degradation of amino acids in liver