Interconversion of Cortisol and Cortisone in Baboon Trophoblast and Decidua Cells in Culture*

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Abstract
In baboons, transplacental cortisol (F)/cortisone (E) metabolism changes from reduction (E to F) at midgestation to oxidation (F to E) near term when estrogen becomes elevated. Indeed, estrogen regulates the placental microsomal 11.beta.-hydroxysteroid dehydrogenase (11.beta.-HSD) enzyme catalyzing F oxidation. However, regulation of 11.beta.-HSD-reductase (E to F) is unknown, because this enzyme is destroyed by microsomal isolation. Therefore, we used cell culture to determine the role of estrogen on placental reduction of E of F and to ascertain whether estrogen regulation of the oxidation of F to E was specific to trophoblast. Placentas were obtained on day 165 (n = 6, term, day 184) and on day 100 of gestation from baboons untreated (n = 8) or treated (n = 6) with 50-mg implants of androstenedione (.DELTA.4A) inserted sc in the mother between days 70 and 100 of gestation to increase placental estrogen production. After removal of fetal membranes, the decidua basalis and trophoblast were separated, rinsed repeatedly in medium-199, minced, and then incubated in trypsin/DNase. Dispersed cells were layered onto a discontinuous Percoll gradient (5-70%), and purified cytotrophoblast (TC; 1.048-1.062 g/ml) and decidua (DC; 1.048-1.062 g/ml) were harvested. After incubation in media containing 10% fetal bovine serum to permit attachment, cells were incubated (24 h) in Dulbecco''s modified Eagle''s medium containing 10,100, or 500 ng [3H]F or [3H]E. F and E in medium were purified by HPLC and the interconversion of F/E calculated. Equilibrium was achieved by 12 h, and F/E metabolism was proportional to cell number and substrate (10-500 ng) concentration. At substrate concentrations of 500 ng/ml, the reduction of E to F (range, 81-195 ng F produced/24 h) in the DC (0.5 .times. 106 cells) was greater (P < 0.05) than oxidation of F to E (19-28 ng E/24 h) in all groups. This pattern of metabolism by DC was not affected by time of gestation or treatment with .DELTA.4A. In the TC (25.5 .times. 106 cells), oxidation of F to E always exceeded (P < 0.05) reduction of E to F. Moreover, the conversion of F to E by TC of day 100 (86 .+-. 26 ng E/24 h; mean .+-. SE) was increased (P < 0.05) by .DELTA.4A (195 .+-. 35) and greater (P < 0.05) at day 165 (213 .+-. 40). In contrast, TC metabolism of E (21-57 ng F/24 h) was similar in all groups. These patterns of F/E interconversion observed at substrate concentrations of 500 ng/ml also occurred when TC and DC were incubated with 10 and 100 ng/ml F or E. Collectively, the results of the present study suggest that placental oxidation of F to E measured in vivo reflects primarily metabolism by the trophoblast, whereas in vivo reduction of E to F reflects primarily metabolism by the decidua. Because neither advancing gestation nor increasing estrogen affected reduction of E to F by the trophoblast or F/E interconversion by the decidua at substrate concentrations ranging from 10 to 500 ng/ml, we suggested that increased placental conversion of F to E in vivo near term is the result of regulation of the 11.beta.-HSD-oxidase enzyme in the trophoblast by estrogen.