Fetal growth and 1,25-dihydroxyvitamin D3 injections into thyroparathyroidectomized pregnant rats

Thyroparathyroidectomy (TPTX) in pregnant rats on day 12.5 of gestation was associated with a progressive reduction of dietary intake between days 18 and 21 of gestation. In control mothers with a similar dietary restriction, the fetal plasma calcium and phosphate levels were unchanged, and a slight decrease in fetal weight (approximately 0.8 g) was observed at term. Maternal hypocalcemia in TPTX animals induced chronic fetal hypocalcemia beginning at day 18.5 of gestation; fetal hyperphosphatemia was only statistically significant on the last day of gestation. Weight, blood glucose and liver glycogen stores, which were greatly decreased in fetuses from untreated TPTX mothers, increased after injection of 1,25-(OH)2D3 into TPTX mothers. A marked increase in fetal weight (+ 1.6-2.0 g) occurred at term with doses ranging from 0.05 to 0.25 micrograms/kg of body weight; higher doses (greater than or equal to 0.5 micrograms/kg) inhibited this improvement. Fetal blood glucose was normalized (approximately 45-50 mg/100 ml) when TPTX mothers received 0.05 to 0.5 micrograms/kg, but decreased with higher doses. The highest fetal liver glycogen store (80 mg/g) was achieved using 0.05 micrograms of 1,25-(OH)2D3/kg, this increment being progressively inhibited when larger doses were given. Subcutaneous calcifications were observed in the fetuses of some litters after treatment of the TPTX mothers with 1 microgram of 1,25-(OH)2D3/kg.