EFFECTS OF A GONADOTROPIN- RELEASING HORMONE AGONIST ON RAT OVARIAN FOLLICLE APOPTOSIS: REGULATION BY EGF AND THE EXPRESSION OF BCL-2-RELATED GENES

PARBORELL F; PECCI A; OLGA GONZALEZ; VITALE A; TESONE M

BIOLOGY OF REPRODUCTION (ONLINE)

Año: 2002 vol. 67 p. 481 - 486

1529-7268

The purpose of the present study was to evaluate the in vivo effect of a GnRH analog (leuprolide acetate, LA) on  follicular development and apoptosis-related mechanisms, in preovulatory ovarian follicles (POF) obtained from prepubertal equineCG-treated rats. Serum progesterone (P) and estradiol (E) levels were measured and a significant decrease in circulating E levels was observed in the LA group, while serum P levels remained unchanged. Ovarian histology revealed an inhibitory effect of LA treatment on the follicular development induced by eCG.  After 48 h of LA treatment, the number of atretic and preantral follicles were increased as compared to controls, while the number of antral follicles had decreased. Cells undergoing DNA fragmentation were quantified by performing in situ 3’-end labeling of DNA with digoxygenin- dUTP on  ovarian sections. LA treatment caused an increase in the percentage of apoptotic cells in preantral and antral follicles. Furthermore, DNA isolated from these POF incubated 24 h in serum- free medium exhibited the typical apoptotic DNA degradation pattern. Treatment of follicles with EGF, suppressed the spontaneous onset of DNA  fragmentation and a similar effect was observed in LA follicles. POF obtained from LA- treated rats showed no changes in Bcl-2 or Bax protein levels. However, a reduction in the Bcl-xL/Bcl-xS ratio was observed, with a greater decrease in Bcl-xL compared to Bcl-xS during the incubation,  suggesting  a lower stability of the Bcl-xL  isoform in the LA group. These results indicate that in vivo GnRH-a treatment produces an increase in the apoptosis process in POF from eCG-treated rats, and that this effect is in vitro reverted by EGF. This GnRH analog also reduced the stability of the Bcl-xL protein,  thus interfering with follicular development by an as yet unknown mechanism