Circaseptan rhythm of corticosterone and lipids in the serum of male rats.

After adaptation to standard conditions and to a 12:12 h light: dark regimen, groups of young SPF male Wistar rats were killed at 8 h on 17 consecutive days and their serum corticosterone and lipid concentrations were determined. Using a combination of a Fourier harmonic analysis and an analysis of variance, the circaseptan rhythm of corticosterone, total cholesterol and triacylglycerol oscillations was determined; it is unlikely that the nonesterified fatty acid concentration has a 7-day rhythm. The circaseptan variation of metabolic and hormonal indicators is evidently adaptive in character and its existence ought to be taken particularly into account in the evaluation of long-term experiments.