Effects of water restriction on circadian rhythms of corticosterone, growth hormone and thyroid stimulating hormone in adult male rats.

The effects of acute and chronic water restriction on the circadian rhythms of corticosterone, growth hormone (GH), and thyroid stimulating hormone (TSH) were studied in adult male rats. Water restricted rats were allowed to drink between 9:00 and 9:30 a.m. only. Chronic water restriction but not one day of such treatment altered the circadian pattern of corticosterone so that a peak of this hormone appeared before water presentation. In contrast, neither acute nor chronic water restriction altered the qualitative patterns of circadian GH and TSH rhythms although both treatments depressed the secretion of the two hormones, the depression being greater in chronic than in acute water restricted rats. These results indicate that water restriction did not resynchronize the GH and TSH circadian rhythms. It appears that reduced secretion of GH and TSH observed in water restricted rats would be due to the concomitant reduction in food intake.