Serum calcium and phosphate concentrations and parathyroid morphology in rats treated with vitamin D metabolites.

The serum concentrations of calcium and phosphate and parathyroid morphology were studied in rats treated with vitamin D metabolites. Twenty hours after a single injection of 1.25-dihydroxycholecalciferol (1.25-DHCC) or 25-hydroxycholecalciferol (25-HCC) the serum calcium and phosphate concentrations were not significantly altered in any group, but the 1.25-DHCC treated rats exhibited an increased number of dark chief cells and occurrence of a few atrophic chief cells. Four to eight weeks after daily injections of the vitamin D metabolites the 1.25-DHCC treated rats exhibited significantly increased serum calcium concentrations and parathyroid glands composed of atrophic and dark chief cells in solid and follicular arrangement, whereas the rats treated with 25-HCC showed unaffected serum calcium concentrations and parathyroid glands composed of solid sheets of light chief cells, often with vacuolated cytoplasm, a few dark chief cells, but no atrophic cells. The findings suggest a direct or indirect suppressive influence of 1.25-DHCC on parathyroid activity in rats.