The disposition of [3H]cortisol after intra-amniotic administration to sheep late in pregnancy.

The disposition of [3H]cortisol was determined after an intraamniotic injection into chronically catheterized sheep between days 120 and 146 of pregnancy. [3H]Cortisol disappeared from amniotic fluid with a half-life of 55.6 +/- 10.8 (SEM) min. Radioactivity, identified as [3H] cortisol appeared in allantoic fluid, fetal blood and tracheal fluid. The concentration of [3H]cortisol in allantoic fluid rose such that it approached that found in amniotic fluid at 60 min after injection. The highest concentration of [3H]cortisol in fetal blood was found 15 min after injection. The time-course for appearance of [3H]cortisol into tracheal fluid was variable, but in individual experiments peak values were found 45-150 min after injection. We conclude that during late gestation, cortisol in amniotic fluid is readily accessible to the allantoic fluid and to the fetus.