Diurnal changes in calcium and phosphate metabolism in rats.

Diurnal changes in the metabolism of calcium and phosphate were studied in fasted conscious rats by use of a perfusion balance study method. On a light dark 12:12 h schedule and on a constant iv load of calcium among other nutrients, the animals exhibited a diurnal rhythm in which urinary excretion of calcium was low in the night and high in the day. This was accompanied by a reciprocal change in phosphate balance (high excretion in the night, and low in the day). The diurnal change was abolished by adrenalectomy. Thyroparathyroidectomy alone did not prevent the diurnal change. It was abolished, however, when thyroparathyroidectomy was followed by a constant infusion of parathyroid hormone (0.8 U/h). These data indicate the presence of a diurnal rhythm of calcium and phosphate metabolism in rats and the involvement of parathyroid and adrenal hormones in the genesis of the rhythms.