The availability of cortisol in amniotic fluid to the fetus and chorionic and amniotic membranes.

This study examined whether cortisol, present in amniotic fluid (AF), could reach the fetal blood, and might be available to various fetal organs and to the fetal membranes and placenta. [3H]Cortisol ([3H]F) was injected into the AF of five sheep at 130--143 days gestation. Samples of AF and fetal blood were collected for 120 min, at which time the fetuses were delivered and fetal organs and fluid were collected for measurement of the [3H]F content. [3H]F disappeared from AF with an initial half-life of about 40 min and was detected in fetal blood by 30 min after intraamniotic injection. At 120 min after injection, [3H]F was widely distributed within the pregnant uterus, and the highest concentrations of radioactivity were found in allantoic fluid, fetal membranes, and placental tissue. The concentration of [3H]F in the umbilical vein was higher than in umbilical arterial blood in four of five sheep. [3H]F and [3H]cortisone were found in several fetal tissues, including adrenal, kidney, pancreas, lung, and liver. [3H]F in tracheal and stomach fluid was generally less than in fetal blood. We conclude that 1) cortisol can reach the fetus from AF, 2) a major route of entry may be via the vasculature of the fetal membranes, 3) a considerable proportion of [3H]F is retained by the fetal membranes, and 4) interconversion of [3H]F and [3H]cortisone may occur in some fetal tissues.