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.
- 11β-Hydroxysteroid dehydrogenase
- Amniotic injection
- Steroid kinetics