Numerous studies have shown that a variety of cytokines are involved in the regulation of ovarian function. Interleukin-6 (IL-6), has been found in follicular fluid. In this report we show by immunocytochemical methods the localization of the extracellular domain of the IL-6-receptor and its associated signal transducer glycoprotein gp 130 on the surface of granulosa cells (GCs). The possibility that IL-6 may also influence the basal and FSH-stimulated production of estradiol (E2) and progesterone (Prog) by GCs in vitro was also investigated. GCs were obtained from infertile patients undergoing in vitro fertilization and embryo transfer treatment and cultured for 72 h or were given increasing concentrations of human recombinant IL-6 (8--128 pg/ml) in the absence or presence of FSH (96 U/ml). For the time-course studies, FSH-stimulated GCs were treated in the absence or presence of IL-6 (128 pg/ml) and supernatants were assayed at 24 h intervals (24-96 h) for E2 and Prog productions. The results show that increasing amounts of IL-6 significantly inhibit E2 production in the absence or presence of FSH vs untreated controls (P=0.025 at IL-6=128 pg/ml and P=0.016 at IL-6=16 pg/ml respectively). IL-6 also inhibited FSH-stimulated but not unstimulated Prog release (P=0.038 at IL-6=8 pg/ml). These findings suggest that IL-6 may be one of the factors that plays a local regulatory role in the course of FSH-stimulated E2 and Prog release. The time-course studies of the effect of the absence or presence of IL-6 demonstrated a significant inhibitory effect on both E2 and Prog secretion (P<0.001) by FSH-stimulated GCs. As infections of the female reproductive tract are often accompanied by elevated local IL-6 levels, this factor may be one of the links leading to endocrine reproductive dysfunction during genital infections.

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