Aspects of circadian periodic changes in phosphorus metabolism in mice

¹ Division of Neurology, University of Minnesota Medical School, Minneapolis, Minnesota

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.

Key Words: intermediary phospholipid metabolism • brain inorganic phosphate • liver phosphate metabolism • plasma • inorganic phosphate turnover

Submitted on August 31, 1962