Transfer of ³h-cortisone and ³h-cortisol between the amniotic, allantoic, and fetal blood compartments in the rabbit at day 25 of gestation

We have examined the rate of disappearance and the form of the radiolabel following the injection of either [1,2-³H]-cortisone (³H-E) or [1,2,6,7,n-³H]-cortisol (³H-F) into the amniotic sac of rabbits at day 25 of gestation. The half-life of³H-E was approximately 35 min and was very much shorter than that of³H-F. Concurrent with the disappearance of³H-E was an increase in the amount of tritium in both the allantoic and the fetal blood compartments. Whereas following injection of³H-E there was a rapid conversion of E to F that was reflected in all three compartments, following injection of³H-F the vast majority of the tritium label remained as F. We conclude that amniotic E may act as a ready source of fetal F.