Plasma calcium control in the rat fetus. I. Influence of maternal hormones

The influence of PTH, calcitonin (CT), and thyroxine deficiencies during pregnancy on fetal plasma calcium and fetal growth has been investigated in thyroidectomized (TX) and thyroparathyroidectomized (TPTX) mother rats complemented or not with thyroxine. Maternal femurs analyses at 21.5 days of gestation in TX and TPTX rats showed a significant decrease in wet and dry weights, whereas percentage of ash and its relative content in calcium and phosphorus was unchanged. Thus, CT during pregnancy seemed to prevent a decrease in the organic part of bone. The fetus from TPTX mothers was characterized by a reduced body weight (-1.95 g) and a 12% drop in its percentage of ash. The length of the fetal femur was 16% decreased, the shaft being mainly affected. It the percentage of ash of the fetal femur was unchanged, its relative content in calcium and phosphorus was decreased. In fetuses from TX mothers, the body weight was slightly decreased (approximately 0.71 g) and the percentage of ash was 5% reduced. The small decrease in the fetal femur length reflected a change at the distal end. Thyroxine complementation in TX or TPTX mothers induced a normalization of the fetal percentage of ash in both cases; a trend towards an increased value was observed in the percentage of ash of fetal femurs. Fetuses from TX mothers exhibited normal plasma calcium values unaffected by maternal thyroxine complementation. The lowered plasma calcium level (approximately 2.5 mg/dl) occurring in fetuses from TPTX mothers was increased by 1 mg/dl after thyroxine complementation of the mother in spite of unaltered maternal plasma calcium levels.