Exogenous corticosteroid and shifts of circadian rhythms in hamsters.
We tested the hypothesis that glucocorticoid stimulation mediates the effect of exercise on circadian clock resetting in hamsters. We injected animals with 1 and 5 mg dexamethasone--a potent glucocorticoid agonist--at zeitgeber time (ZT) 4 and ZT6, circadian phases at which vigorous exercise induces maximal phase advances of about 3 h. Neither dose of dexamethasone induced phase shifts that were significantly larger than those induced by injections of saline vehicle at either of the phases tested. Some animals, however, showed quite large and consistent phase shifts to repeated injections whether with saline or dexamethasone, such that there was a statistically significant correlation between individuals' responses to the two treatments. The data indicate no role for increased glucocorticoid activity in mediating the effects of exercise on circadian phase shifting, but suggest a modest role for nonspecific stimulation, independent of exercise, in inducing phase shifts at ZT4-ZT6.
Janik
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Biology Department, University of Wisconsin-Eau Claire, 54702, USA. janikds@uwec.edu
Nest
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KJ
Janiga
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MA
D000305:Adrenal Cortex Hormones / Q000494:pharmacology*; D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects*; D006224:Cricetinae; D003907:Dexamethasone / Q000494:pharmacology; D008297:Male; D008647:Mesocricetus; D008954:Models, Biological; D009043:Motor Activity / Q000187:drug effects; D017440:Photoperiod
D000305:Adrenal Cortex Hormones; D003907:Dexamethasone