The effects of subdiaphragmatic vagotomy on circadian corticosterone rhythmicity in rats with continuous or restricted food access.

Plasma corticosteroid circadian periodicity was determined in three groups of individual adult male rats. Categories were: post-subdiaphragmatic vagotomy, sham-operated, and controls. Blood was sampled every 4 hours over a 48-hour period with ad lib feeding and after a 13-day period on daytime (0930--1330) restriction of food and water availability. Plasma corticosterone circadian periodicity was normal under ad lib conditions in control, sham-operated, and vagotomized animals. Under food-restricted conditions, both the sham-operated and vagotomized animals exhibited the 12-hour shift in the circadian peak of plasma corticosterone levels that we have previously described in normal animals under such conditions. There were no differences between groups in the total amount of food and water consumed or the percentage of nocturnal food intake on an ad lib feeding schedule. Both vagotomized and sham-operated animals manifested reductions in food intake under conditions of food restriction, although vagotomized consumed less than sham-operated animals. The present data indicate that an intact vagus nerve is not necessary for the establishment of circadian periodicity of plasma corticosterone levels or the shift in the periodicity of corticosteroid secretion produced by a restricted feeding regimen.