Gonadotrophic regulation of prolactin mediated progesterone secretion in vitro

Abstract

Abstract. The effects of preincubating rat granulosa cells with FSH, LH, and Prl on subsequent Prl mediated progesterone secretion were investigated. Granulosa cells were isolated from ovarian follicles 50 h after injection of 5 IU PMSG and were then plated on poly-l-lysine coated coverslips in serum supplemented medium. Cells were preincubated for 24 h in the absence of hormones (control) or with the addition of either 0.25, 2.5, 25 ng/ml rat FSH or rat LH, or 1 μg/ml rat Prl. Following the preincubation period, cells were maintained for an additional 6 or 8 days in the presence or absence of 1 μg/ml Prl. When cells were preincubated with FSH or LH, only the two higher concentrations (2.5 and 25 ng/ml) stimulated significantly more progesterone secretion than control cultures during the 24 h preincubation period. For each series of preincubations, cells cultured for 6 or 8 days in the presence of Prl secreted significantly more progesterone at each day of culture than cells cultured without Prl. Cells preincubated and cultured with Prl secreted only 3–7-fold more progesterone than cells preincubated in control medium and then cultured with Prl. Preincubation with FSH or LH promoted a 20–45-fold increase in Prl mediated progesterone secretion compared to control preincubation cultures that also subsequently were cultured with Prl. The magnitude of Prl mediated progesterone secretion observed through 6 days of culturing was dose dependent on the preincubation concentration of FSH or LH. The establishment of an in vitro model system in which gonadotrophins enhance the responsiveness of granulosa cells to Prl in serum supplemented medium provides the opportunity for study of the regulatory mechanisms involved with the induction and maintenance of such responsiveness.