ABSTRACT
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.
Subject(s)
Adrenal Cortex Hormones/pharmacology , Circadian Rhythm/drug effects , Animals , Cricetinae , Dexamethasone/pharmacology , Male , Mesocricetus , Models, Biological , Motor Activity/drug effects , PhotoperiodABSTRACT
The objective of this study was to determine if the ingestion of snow contaminated with Chlamydomonas nivalis causes diarrhea. The design was a single-blind crossover. Subjects were seven healthy volunteers, aged 24-56 who ingested 500 g of snow contaminated with C. nivalis. Outcome was measured by stool and diarrhea frequency. No differences in stool or diarrhea frequency were noted between treatment and placebo groups. The conclusion is that in this pilot study, there was no evidence supporting the concern that ingestion of "red snow" causes diarrhea.
