Basal bone resorption in the rat fetus related to the hormonal status of the mother.

Fetal bone resorption was measured by an organ culture technique using fetuses from thyroparathyroidectomized (TPTX) pregnant rats to investigate the roles of fetal and maternal hormones in the regulation of basal bone resorption in utero. Thyroparathyroidectomized female rats were treated with thyroxine and/or metabolites of vitamin D3. Basal bone resorption was greatly increased in fetuses from TPTX mothers. Administration of 1,25-dihydroxycholecalciferol or 1,24,25-trihydroxycholecalciferol to TPTX female rats normalized the basal bone resorption of the fetus whereas injection of 24,25-dihydroxycholecalciferol was without effect. Treatment of the TPTX mothers with thyroxine was also shown to normalize basal bone resorption in the fetus.