PLACENTAL METABOLISM OF CORTISOL AT MID-GESTATION AND LATE-GESTATION IN SWINE

An experiment was conducted in pigs to determine the source of fetal c ortisol at 50 (n = 5) or 100 days (n = 4) of gestation (term = 114 day s). Equilibrium concentrations of tritiated cortisol were achieved, an d all hormonal measures were made at 110, 130, 140, and 150 min in ane sthetized pigs. Maternal plasma cortisol did not differ (p = 0.48) bet ween 50 (70.2 +/- 7.4 ng/ml; mean +/- SEM) and 100 days (62.4 +/- 5.8 ng/ml). Conversely, fetal cortisol increased (p = 0.048) between 50 (8 .5 +/- 2.5 ng/ml) and 100 days (24.2 +/- 4.2 ng/ml), and, at each gest ational age, values were lower (p = 0.001) than those in maternal plas ma. Plasma cortisone (15.1 +/- 2.3 ng/ml) did not change with gestatio nal age (p = 0.42) in either compartment (maternal or fetal), nor did it differ between compartments (p = 0.08). Maternal cortisol accounted for 22.8 +/- 2.0% of fetal cortisol at 50 days of gestation, and this contribution decreased (p < 0.001) to 5.87 +/- 0.8% at 100 days. At b oth ages, maternal cortisol accounted for almost 50% of fetal cortison e. Metabolism of maternal cortisol by the entire uterofetoplacental un it was 8.4 +/- 1.7% at 50 days and 7.5 +/- 2.4% at 100 days (p = 0.76) . The maternal metabolic clearance rate of cortisol increased 44% (p = 0.003) between 50 and 100 days (1.49 +/- 0.4 vs. 2.15 +/- 0.2 L/min). Hence at these gestational ages, the fetus-presumably the fetal adren al-is the primary source of fetal plasma cortisol. The major contribut ion of maternal cortisol to fetal cortisone strongly suggests the pres ence of porcine placental 11 beta-hydroxysteroid dehydrogenase activit y. Further, factors constituting the placental ''barrier'' that metabo lize maternal cortisol to cortisone and other products may be major re gulators of porcine fetal plasma cortisol and cortisone.