Diurnal patterns of DNA synthesis in the rat: modification by diet and feeding schedule
Dallman, P.R.; Spirito, R.A.; Siimes, M.A.
Journal of Nutrition 104(10): 1234-1241
1974
ISSN/ISBN: 0022-3166 PMID: 4472065 Document Number: 70509
The diurnal pattern of DNA synthesis was studied in young rats 28 to 35 days old fed on a normal or a protein-deficient diet. All rats were exposed to a 12-h light and dark cycle. With a stock diet to appetite the incorporation of thymidine-3H into nuclear DNA in liver changed over a fivefold range with a peak at the end of the dark period, whereas incorporation into mitochondrial DNA scarcely varied. A diet containing only 3.5% protein decreased the incorporation of thymidine-3H into liver DNA but also obscured the diurnal peaks observed in animals on diet with 26% protein. The activity of thymidine kinase was depressed, but the diurnal peak was still discernible though slightly delayed. The effect of feeding schedule was then studied by restricting the feeding period of a stock diet to either the first 8 h of the dark period (close to normal feeding behaviour) or to the first 8 h of light. The 12-h difference in the feeding period resulted in a closely corresponding difference in the timing of the peak incorporation of thymidine-3H into DNA. In rats gradually adapted to a 4-h feeding schedule over a period of 10 days, there was a briefer but prominent peak of incorporation about 12 h after the onset of feeding. A smaller peak was concurrently present in the adrenals but in skeletal muscle, intestinal mucosa and bone marrow there was no clear pattern of deviation from the 24-h mean values. The results indicate that in contrast to nuclear DNA, there is no prominent diurnal peak of mitochondrial DNA synthesis in liver; the peak of nuclear DNA synthesis in liver is obscured by a protein-deficient diet; the peak follows feeding of a normal diet by about 12 h, independently of the light-dark cycle; and with the exception of the adrenals, other tissues studied did not reveal a food-dependent peak of DNA synthesis.