Transplacental effects of estrogen on osteogenesis in rat foetuses

Pregnant rats were treated with intramuscular injections of 0.2 mg estradiol valerianate dissolved in olive oil on days 12, 15 and 19 of gestation. Controls received olive oil only. Foetuses were removed on the 22nd day of gestation. Estradiol valerianate caused hyper-calcaemia in the treated rats and their foetuses. The foetuses and the placentae were smaller than in the controls. Foetal bones were short, and contained a higher concentration of calcium. The main microscopic alterations of foetal bones were persistence of enchondral trabeculae in the short diaphysis and a reduced number of osteoclasts. Islets of mineralized hypertrophic cartilage were also found surrounded by a thin layer of bone. It is presumed that estradiol valerianate passes through the placenta and affects the foetal skeleton in its early phase of formation, resulting mainly in decreased bone resorption.