Maternal-fetal relationships in the parathyroidectomized rat. Intestinal calcium transport, serum calcium, immunoreactive parathyroid hormone and calcitonin.

We studied the role of the parathyroids in the adaptation of intestinal Ca transport that occurs during pregnancy, and whether maternal hypoparathyroidism causes fetal hyperparathyroidism. Serum Ca of pregnant parathyroidectomized (PTX) rats was significantly greater than nonpregnant, PTX animals. Intestinal active Ca transport was increased 2.1- and 2.2-fold by pregnancy in intact and PTX rats, respectively. Serum levels of immunoreactive parathyroid hormone (PTH) were nondetectable in PTX-pregnant rats. Fetuses from PTX rats appeared grossly normal. The serum PTH was not different in fetuses from PTX compared to fetuses from intact mothers and serum Ca, Mg, and P were normal. Thus, alleviation of maternal hypocalcemia during pregnancy in PTX rats may be due to an adaptive increase in intestinal Ca transport, which does not require the parathyroids. Fetuses from PTX mothers were euparathyroid and were protected from Ca deficiency during pregnancy.