Chronopharmacologic aspects of hexobarbital oxidation rate in rats.

Circadian variations of hexobarbital oxidation rate in rat liver and the relationship to serum corticosterone levels were determined in 324 animals subjected to different lighting regimen and feeding schedules.--Rats maintained under standard light/dark conditions and with free access to food showed a significant circadian hexobarbital oxidase rhythmicity. Inversion of the light/dark cycle and time feeding was followed by significant changes of the 24-h means of hexobarbital oxidation rate as well as of the shape and phasing of the circadian pattern. The animals' response to the experimentally altered environmental conditions did not reveal a predictable relationship between the shape and phasing of the rhythmic patterns of liver hexobarbital oxidase activity and of corticosterone levels in blood serum; the rats subjected to timed feeding showed decreased levels of corticosterone whereas the hexobarbital oxidation rate of the liver was increased.