Circadian rhythm of serum and tissue lipids in the rat: the effect of limited access to food.

Young male Wistar rats of a conventional breed were kept 4 weeks in a separate room with a light: dark regimen of 12:12 h. Some were fed ad libitum (group C, the control), some were meal-fed from 8.30 to 10.30 a.m. (group A) and the others were meal-fed from 8.30 to 10.30 p.m. (group B). When adapted to the nutritional regimen the animals were decapitated at 3-hour intervals, starting at 8 a.m., and their serum and epididymal tissue non-esterified fatty acid values, their serum and liver triacylglycerol and total cholesterol levels and their serum phospholipid concentration were determined. Limitation of the period for which they had access to food at different times of the day significantly synchronized the circadian oscillations of their serum and tissue lipid levels. The most pronounced differences in the form of the antiphase position of the maxima of the curves in groups A and B, or A and C, were recorded in the oscillations of the serum and white adipose non-esterified fatty acid values, in serum triacylglycerol levels and in liver cholesterol levels. It is reasonable to assume that the synchronizing role of timed meal-feeding will be subject to the influence of seasonal factors.