PARENT SESSION

(M631) DYNAMIC MODULATION OF StAR (STEROIDOGENIC ACUTE REGULATORY PROTEIN) AND CYTOCHROME P450C17 BY A GONADOTROPIN-RELEASING HORMONE (GnRH) AGONIST IN RAT OVARIAN FOLLICLES.

Irusta, Griselda¹, Parborell, Fernanda¹, Gonzalez, Olga¹, Tesone, Marta, ¹ Instituto de Biología y Medicina Experimental, Ciudad de Buenos Aires, Argentina

ABSTRACT- It has been demonstrated that GnRH and its analogs may produce in the ovary direct inhibitory effects on follicular development associated by changes in steroidogenesis and apoptosis. Our objective was to study the direct action of a GnRH agonist (Leuprolide Acetate, LA) on ovarian steroidogenesis in antral follicles obtained from prepuberal rats treated with eCG (Control group) or eCG+LA (2 g/rat, LA group) and sacrificed at different time points after the injections. The ovaries were fixed in formalin and used for immunohistochemistry (IHC) of StAR. In addition, antral follicles (>400 m) from ovaries were dissected microscopically and analyzed to detect cytochrome P450C17 alpha- hydroxylase RNAm and protein levels by RT-PCR and western blot, respectively. By qualitative analysis of IHC studies, we observed a moderate signal for StAR only in preantral follicles from LA group after 2h of treatment. At 8h, control and LA group showed a higher expression of StAR compared to 2h, in preantral as well as antral follicles. In addition, at this time, the expression was more intense in LA group compared to control group and the changes in StAR expression were mainly observed in theca cells of these follicles. This higher expression observed for StAR protein, was correlated with a significant increase in serum progesterone levels in LA group (4 fold; p<0.05) after 8h of LA injection. These data were coincident with our previous results that showed a quantitative increase of follicular StAR expression by LA. By contrast, the mRNA and protein levels of P450C17 enzyme in antral follicles were inhibited after 8 h of LA injection (7 and 2 fold, respectively, p <0.05). Correspondingly, this inhibition was reflected in serum androsterone levels (2.5 fold, p<0.05) compared to control group. These results of androgen synthesis were confirmed by in vitro assays, where a 2.3 fold decrease (p<0.05) was observed in the follicular androsterone content of antral follicles (24h incubation with FSH+LA). We conclude that GnRH agonist affects the ovarian steroidogenic pathway, increasing StAR expression in theca cells, but diminishing follicular androgen synthesis and consequently, reducing the supply of estrogens available to developing follicles. Supported by the ANPCYT (BID 1201 OC-AR PICT 99:05-06384 and University of Buenos Aires-X237).

KEY WORDS: ovary, GnRH-agonist, Steroidogenesis, StAR-CYP17