Cortisol:cortisone interconversion by human decidua in relation to parturition: effect of tissue manipulation on 11 beta-hydroxysteroid dehydrogenase activity.

Cortisol:cortisone interconversion was studied in human decidua obtained from three groups of patients at term (37-42 weeks): before the onset of labour (at elective Caesarean section), after labour of spontaneous onset, and after labour of induced onset. When intact tissue was incubated with [3H]cortisol or [3H]cortisone in phosphate buffer without added substrate or cofactors, cortisone to cortisol was the dominant conversion. However, when damaged cells or tissue homogenates were used in the same conditions, the dominant direction of the reaction was reversed, with a large increase in oxidative (cortisol to cortisone) activity. Cortisol:cortisone interconversion was similar in the three groups of samples using either intact tissue or homogenates, as was the total 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) activity measured in tissue homogenates in the presence of added substrate (cortisol or cortisone) and cofactors (NADP+ or NADPH). Endogenous cortisol concentrations in decidua were higher than those of cortisone, and the ratio of cortisol to cortisone was similar in the three groups. These findings suggest that there are no changes in human decidual 11 beta-HSD activity in relation to parturition. Specific activity of 11 beta-HSD decreased at high protein concentrations, suggesting the presence of some enzyme inhibitor(s) in homogenized decidual tissue.