Time Relations Among Metabolic and Morphologic 24-Hour Changes in Mouse Liver

Abstract

Phospholipid and RNA metabolism in immature mouse liver, in different cell fractions obtained by centrifugation, are 24-hour periodic. Twenty-four-hour rhythms also characterize the metabolism of DNA and mitotic activity. The established 24-hour rhythm in liver glycogen content stands out clearly under standardized circumstances of observation. Some peaks and troughs of these rhythms are dissociated in time. To the extent that radiotracer methods used herein indicate formation of the metabolic variables studied, it may be inferred that, ordinarily, in immature mouse liver, the peak formation of both phospholipid and RNA consistently leads in phase 1) peak DNA formation by 6–8 hours; 2) peak glycogen content by about 12 hours; and 3) peak mitotic activity by about 16 hours. Phase-differences among the curves describe a sequential order among certain metabolic and morphologic events at the intracellular level, as well as the time relations of these events. Since the curves for nuclear and cytoplasmic RNAs are more congruous than those for nuclear RNA and DNA metabolic rather than localized intracellular factors probably underlie this periodicity.