A novel steroidogenic role of suramin-blocked luteal cell growth factors

Growth factors synthesized in the ovarian corpus luteum (CL) have been implicated in the development of the CL. One of these growth factors is basic fibroblast growth factor which acts on luteal cells in an autocrine manner (Tamura et al. 1991; Asakai et al. 1992). To elucidate effects of these growth factors in the development of the CL, we cultured immature luteal cells with defined medium for a week in the presence or absence of a growth factor inhibitor, and measured progesterone in the medium as an indicator of cell differentiation. Culture of luteal cells showed an increased amount of progesterone for three days and continued to synthesize progesterone for at least another four days without serum and pituitary hormones. The addition of suramin, previously reported to inhibit autocrine growth stimulation, accelerate the daily progesterone production of luteal cells apparently by switching on the early onset of differentiation. Suramin also induced apoptosis of the cells after the 3rd day of culture. These data suggest that an autostimulation mechanism by growth factors plays a physiological role on normal cell differentiation, and it is not limited to neoplastic transformation.