Healthy women and patients with endometriosis show high concentrations of inhibin A, inhibin B, and activin A in peritoneal fluid throughout the menstrual cycle.

Inhibin A, inhibin B, and activin A are growth factors which play local autocrine/paracrine roles in reproductive tissues. Since peritoneal fluid hormone content may reflect in part ovarian and endometrial secretory activities, the present study aimed to evaluate: (i) whether inhibin alpha-, activin betaA- and betaB-subunits, and activin receptor type II and type IIB mRNA are expressed in peritoneal tissues; (ii) expression and secretion of inhibin A and B, and activin A in cultured endometriotic cells; and (iii) concentrations of inhibin A and B, and activin A in serum and in peritoneal fluid in healthy women and in patients with endometriosis throughout the menstrual cycle. A group of women (n = 72) was recruited at laparoscopy for infertility investigation and divided into two groups: (i) control healthy women (n = 35), (ii) women with endometriosis (n = 37). Both groups were subdivided according to the follicular and luteal phase of the menstrual cycle. At the time of laparoscopy, specimens of peritoneal tissues were collected from three healthy women, while endometriotic tissue samples were collected and cultured from three women with endometriosis. Peritoneal tissues and cultured endometriotic cells expressed inhibin alpha-, activin betaA-, and betaB-subunits, and activin receptors mRNAs; in addition, inhibin-related proteins were measurable in culture medium. In healthy women, inhibin A and B, and activin A concentrations in peritoneal fluid were significantly higher than in serum (P < 0.001), at both phases of the menstrual cycle. Peritoneal inhibin A and B, and activin A concentrations were not significantly different between healthy women and patients with endometriosis, either when evaluated according to the degree of the disease and/or to the phase of the menstrual cycle. In conclusion, the findings that high concentrations are present in peritoneal fluid and that menstrual cycle-related changes occur suggest that reproductive organs may contribute to inhibin-related proteins in peritoneal fluid.