Effect of fasting on the circulating glucose and insulin levels after glucose, arginine, pyruvate and palmitate administration in the rat.

Abstract

The effect of glucose, arginine, pyruvate and palmitate administration on levels of circulating glucose and RIA-insulin was studied in fed and 48 h-fasted rats. The rise in blood glucose level after oral glucose load was greater in fasted than in fed rats, whereas plasma insulin level increase was similar in both groups. When glucose was given intravenously, plasma RIA-insulin rose only in the fed animals. Arginine administration produced minor changes in these parameters in both fed and fasted rats. Oral pyruvate produced greater enhancement in blood glucose concentration in fasted than in fed animals while plasma insulin levels rose only in the fed rats. After palmitate load, blood glucose levels increased only in the fed animals in which there was also an increase in plasma insulin levels following intravenous administration of fatty acid. These results suggest that none of the metabolites used except glucose has a physiological role in insulin secretion in the fed or fasted animals; in the latter group sensitivity to glucose stimulus was greatly reduced while the release of insulinotropic gastrointestinal factors after administration of oral glucose appeared less affected. The changes in blood glucose levels observed after addition of pyruvate or palmitate are discussed in terms of the role of pyruvate as a gluconeogenetic substrate and of the effect of palmitate on glucose metabolism.