Tibolone and metabolites induce prolactin production in human endometrial stromal cells in vitro: Evidence for cell-specific metabolism

In this study, we assessed the effects of tibolone and its metabolites on the production of a progesterone sensitive parameter, prolactin, in human endometrium stroma cells in vitro. In addition, the metabolism of the compounds by isolated stromal and epithelial cells was evaluated. The reference compounds, progesterone, Org 2058, and DHT all induced prolactin production. Oestradiol also slightly induced prolactin production and enhanced the response to Org 2058. Tibolone and Delta(4)-tibolone were similar with regard to potency to induce prolactin levels in the culture supernatant. Their potency was lower than that of Org 2058, similar to that of progesterone and higher than that of DHT. The efficacies of tibolone, Delta(4)-tibolone and Org 2058 were similar (similar to 200-fold induction). The estrogenic tibolone metabolites 3 alpha- and 3 beta-OH tibolone also significantly stimulated prolactin production. Their potency, however, was low since significance was reached only at the highest concentrations tested. The PR antagonist Org 31710 inhibited both tibolone- and Delta(4)-tibolone-induced prolactin production. The responses of fibolone and Delta(4)-tibolone were not affected by co-incubation with the androgen receptor antagonist OH-flutamide. The effect of tibolone, but not Delta(4)-tibolone, was antagonized approximately 50% in combination with the highest dose (1 mu M) estrogen receptor antagonist, ICI 164384. The induction of prolactin by 3 alpha- and 3 beta-OH tibolone was antagonized most potently by Org 31710, but also by ICI 164384 and OH-flutamide. Tibolone is metabolized differently in epithelial and stromal cells of the human endometrium. The epithelial cells mostly produce the progestagenic/androgenic Delta(4)-tibolone. The stromal cells produce predominantly the 3 beta-OH tibolone, and some Delta(4)-tibolone, but the net effect observed with regard to prolactin production is progestagenic. When the metabolites 3 alpha-OH, 3 beta-OH, and Delta(4)-tibolone were added to the cultures no conversions were observed. The HPLC analyses showed no evidence for the production of sulfated metabolites. In conclusion, the net effects on endometrial stromal cells are predominantly progestagenic. Tibolone is converted by epithelial cells into Delta(4)-tibolone which displays progestagenic and androgenic activities, whereas in stromal cells also the estrogenic metabolites 3 alpha- and 3 beta-OH fibolone are formed. (c) 2006 Elsevier Ltd. All rights reserved.