Aspects of circadian periodic changes in phosphorus metabolism in mice

Abstract

Kinetic studies on the P32 content of mouse brain phosphorus fractions following the intraperitoneal injection of P32-labeled orthophosphate were performed during two selected segments of the 24-hr time scale. The results of these studies suggest that the circadian periodicity in relative specific activity of brain phospholipids is probably a consequence of a variation in the extent of P32 incorporation into brain inorganic phosphate and is not indicative of a periodicity in the rate of intermediary phospholipid metabolism. Data on the postinjection time course of the specific activities of plasma inorganic phosphate, liver inorganic phosphate, and liver phospholipid suggest a similar explanation for the circadian periodic changes in relative specific activity of liver phospholipids. A circadian rhythm of inorganic phosphate concentration in mouse plasma is demonstrated. Consideration of a mathematical model suggests that the observed within-day variation in P32 distribution and the circadian periodicity of phospholipid relative specific activity in liver and brain are a consequence of this periodicity in plasma phosphate content. A significant within-day variation in total phosphorus content of liver was observed. The disturbance of mice incident to P32 injection has a marked effect on the plasma content of inorganic phosphate and corticosterone.

Advances in understanding of phosphate homeostasis and related disorders

“…The peripheral circadian clock is also entrained by various factors, such as restricted feeding. Serum levels of phosphate have been shown to exhibit a circadian profile in both mice and humans [139,140], indicating the regulation of Pi metabolism by the circadian clock system. Sympathetic tone also displays a circadian profile and is activated by food intake, and we previously suggested that food intake-associated sympathetic activation was involved in the regulation of Pi metabolism [121].…”