Conversion of cortisol to cortisone by the human uterus and its reversal in pregnancy.

Inter-conversion of cortisol (F) and cortisone (E) was investigated by incubating minced tissue with tritiated cortisol or cortisone and then separating the products by Sephadex LH-20 column chromatography. In non-pregnant subjects conversion of F to E predominated (43.4+/-3.4% vs 0.1+/-0.4% for E to F). In early pregnancy F leads to E decreased and E leads to F rose while at term E leads to F (46.3+/-9.1%) exceeded F leads to E (15.1+/-6.8%). These results were in accord with those obtained by assaying the endogenous concentrations. In non-pregnant subjects the F/E ratio (1.1+/-0.6) was lower than that found in serum (6.3+/-2.2) while at term the uterine F/E (9.0+/-1.8) was similar to that of serum (8.8+/-2.0). These changes resulted in an 8-fold increase in uterine F compared with a 3-fold increase in serum F, while uterine E fell to 1/2 and serum E doubled. Thus, during pregnancy there is a dramatic reversal of the reaction in the uterus in favour of the active hormone. It seems possible that the increase in cortisol thus brought about may play an anti-immune role in uterine wall, the single tissue apart from blood in direct contact with fetal tissue.