Plasma glucagon, glucose, insulin, and motilin in rats anticipating daily meals

The circadian food entrainable oscillator (FEO) mediates an increase in act ivity preceding access to periodic meals. The FEO is anatomically independe nt of the suprachiasmatic nucleus (SCN), but its locus remains to be establ ished. Whether the FEO is located in the central nervous system (CNS) or in the periphery, it seems reasonable to assume that there is a link of commu nication between the digestive system and the CNS because only nutritive me als entrain the FEO. Subdiaphragmatic vagotomy and visceral deafferentation with capsaicin do not eliminate food-anticipatory activity (FAA), indicati ng that a neural signal is not necessary. The present study investigates th e hypothesis that humoral signals from the digestive system act upon the CN S to trigger or entrain FAA. Intact rats and rats with SCN lesions were ent rained to daily meals and then sacrificed prior to FAA or during FAA, but b efore meal access. Average plasma concentrations of glucose and insulin wer e nearly identical in both groups. Plasma and duodenal mucosal motilin conc entrations also were not different between the two times. Corticosterone wa s elevated during anticipation, but the difference was not statistically re liable. Glucagon concentration was decreased during FAA compared to concent ration prior to FAA in both intact and SCN-lesioned subjects. This differen ce was not observed in control rats fasted for the same number of hours, bu t not previously entrained to a daily meal. Although the decrease in glucag on could be a signal that initiates FAA, a causal role remains to be establ ished. (C) 1999 Elsevier Science Inc.