Influence of the light regimen on the circadian rhythm of serum lipids in the laboratory rat.

Young male rats of a conventional Wistar breed were adapted for several weeks (3-6) to a 12:12 h light:dark (7 a.m. - 7 p.m., 7 p.m. - 7 a.m.) regimen (LD), to inversion of this standard regimen (DL), to continuous darkness (DD) or to continuous light (LL). After adaptation, groups of animals were killed at 3-hour intervals during the day and the basic lipid fractions were determined in their serum. Under the standard light regimen the cosinor test demonstrated a rhythm in all the indicators (triacylglycerols, total cholesterol, phospholipids) except for non-esterified fatty acids. When the regimen was inverted (DL), the peaks of the circadian non-esterified fatty acid and triacylglycerol curves shifted to the antiphase. The acrophases of "free-running" serum lipid rhythm under the DD regimen of the standard regimen rhythms differed in the case of cholesterol and phospholipids. In the case of triacylglycerols and phospholipids there was disagreement between the DD and LL regimen curves. With reference to the localization of the acrophase under the DD and LD regimens it was assumed that the influence of the light regimen on the synchronization of circadian rhythms is small in the case of serum non-esterified fatty acids and triacylglycerols and that it is greater in the case of serum cholesterol and phospholipids.