Selective depression of prefeeding corticosterone peak in rat by sodium pentobarbital injection

Dependency of prefeeding corticosterone peak on the time of meal supply and effects of an anesthetic, sodium pentobarbital, on both prefeeding and light-entrainable circadian hormone peaks were examined in rats. The prefeeding hormone peak which developed under restricted feeding was more prominent when rats had access to meal in the evening than in the morning. However, the increment of the hormone level above the baseline was greater in the morning than in the evening. An intraperitoneal injection of pentobarbital depressed the prefeeding hormone peak to the baseline level of circadian excursion at both times of day, but did not affect the light-entrainable circadian rise of the hormone level. It is concluded that the magnitude of prefeeding corticosterone peak under restricted feeding depends on the time of day and the mechanism behind the hormone peak was different from that underlying the light-entrainable circadian rhythm in that the former is sensitive to pentobarbital while the latter is insensitive to it.