Restoration of corticosteroid periodicity in obese rats by limited a.m. food access.

Absence of circadian periodicity of plasma corticosteroid levels has previously been reported to occur in animals maintained under constant light and in animals with suprachiasmatic nuclear lesions. Such animals also exhibit aperiodic rather than normal nocturnal eating. Restricted a.m. access to food (09.30--11.30 h) in such animals results in appearance of circadian corticosteroid periodicity (peak at 08.00 h) similar to that seen in normal animals on a similar food restriction regimen. The present study investigated the nature of adrenal circadian periodicity in obese rats who are reported to exhibit aperiodic feeding. Such aperiodic feeding occurred in obese male, but not in obese female, animals. These obese male animals manifested absent corticosteroid circadian periodicity. Restricted a.m. access to food was associated with the appearance of such periodicity similar to that described above in the two other experimental situations. These studies indicate differences in eating behavior and corticosteroid periodicity between obese male and obese female rats. They provide additional confirmation, in animals under normal light--dark conditions and in the absence of CNS lesions, of the role of periodic feeding in the generation of adrenal circadian periodicity.