[Effect of weightlessness on the skeletal development of the rat fetus].

The size of the ossified areas of skeletal bones of fetuses of white rats flown onboard Cosmos-1514 during their pregnancy days 13 to 18 was compared with that of synchronous and vivarium controls. The effect of zero-g on the pregnant animals in the course of an active formation of fetal bones involved a distinct (13-17%) arrest of the development of nearly every area of the fetal skeleton. The signs of the arrest development were more manifest in less mature skeletal structures. Since the Ca2 content was identical in the flight and control rats, it can be concluded that the inhibited ossification of the flight fetuses was produced by the impairment of mechanisms controlling Ca2+ incorporation into the growing skeleton. The ossified areas in the skeleton of the flight newborns were significantly larger than those of the synchronous and vivarium controls. This means that during the readaptation period (pregnancy days 18 to 23) the inhibited ossification of the fetal skeleton was completely compensated and that the flight newborns (i. e. the rats whose prenatal development occurred in part in zero-g) were ahead of the controls with respect to the ossification rate.