BILATERAL LESIONS OF THE SUPRACHIASMATIC NUCLEUS ENHANCE GLUCOSE TOLERANCE IN RATS

Abstract

Rats with or without lesions of the suprachiasmatic nucleus (SCN) were kept under a 12-h light (0800-2000) and 12-h dark (2000-0800) cycle, and oral and intravenous glucose tolerance tests were performed in the light period (at 1000) and dark period (at 2200). In control rats, glucose tolerance was higher in the dark period than in the light period in both tests, though increase in plasma insulin was significantly higher in the dark period than in the light period only in the intravenous test. Lesions involving the bilateral SCN markedly increased glucose tolerance and insulin secretion after oral and intravenous glucose loads in both the light and the dark period, and there was no difference between the results of either test in the light and the dark period. These findings suggest that in rats, glucose tolerance shows a daily rhythm and that the SCN may be involved in generation of this rhythm through photoperiodic control of insulin secretion.