1,25-Dihydroxyvitamin D3 injections into rat fetuses : effects on fetal plasma calcium, plasma phosphate and mineral content

The in vivo effects of 1,25-(OH)2D3 were assessed using fetuses from normal and thyroparathyroidectomized (TPTX) pregnant rats. 21.5-day old decapitated fetuses from TPTX mothers exhibited lowered basal plasma calcium, elevated basal plasma phosphate and an increased percentage of total ash compared to intact littermates. In decapitated fetuses from normal mothers, neither plasma calcium nor plasma phosphate was changed. Subcutaneous injection of 1 micrograms of 1,25-(OH)2D3/kg of body weight to 19.5-day old fetuses (intact or deprived of their parathyroid glands by decapitation) from TPTX mothers induced a marked rise in plasma calcium levels (2.01 and 3.66 mg/dl, respectively) 48 h later. Little change occurred in fetuses from normal mothers (1.06 mg/dl in decapitated and no change in intacts). A decrease in plasma phosphate levels was observed with the same dose in both decapitated and intact fetuses from TPTX mothers (- 1.39 and - 0.65 mg/dl, respectively), while no modification was found in fetuses from normal females. Therefore, the hypersensitivity of fetuses from TPTX mothers to 1,25-(OH)2D3 was unrelated to the development of the fetal hyperparathyroidism secondary to maternal TPTX. The percentage of ash was unchanged in decapitated fetuses from TPTX mothers and was increased in intact littermates after 1,25-(OH)2D3 treatment. However, these values for total ash may represent alterations in bones and/or soft tissues.