EFFECT OF GONADOTROPINS ON THE ABILITY OF 5,6-DICHLORO-1-BETA-D-RIBOFURANOSYLBENZIMIDAZOLE (DRB) TO INHIBIT GERMINAL VESICLE BREAKDOWN IN BOVINE OOCYTES

The transcriptional inhibitor, 5,6-dichloro-1-beta-D-ribofuranosylbenz imidazole (DRB), prevents germinal vesicle breakdown (GVBD) in bovine oocytes only in the presence of gonadotropins. The objectives of this study were to examine the ability of gonadotropins to facilitate trans criptional inhibition of GVBD in bovine oocytes and to examine the eff ect of gonadotropins on transcriptional inhibition of cumulus expansio n. Cumulus-oocyte complexes (COG) from 2 to 7 mm follicles were cultur ed in TCM-199 with 1 mu g/ml estradiol, 50 mu g/ml gentamicin and horm onal treatments for 20 to 24 h at 39 degrees C in 5% CO2 in air. After culture, COC were assessed for degree of cumulus expansion and oocyte s were then denuded, fixed and stained to determine stage of meiosis. In the presence of LH and FSH the proportion of oocytes arrested at ge rminal vesicle (GV) stage was significantly increased with DRB treatme nt (58 vs 3% GV for LH/FSH+DRB vs LH/FSH-DRB; P<0.001). However, maxim al inhibition of GVBD by treatment with DRB could also be achieved in the presence of FSH alone (60% GV for FSH+DRB). The ability of DRB to block GVBD was significantly reduced in the presence of LH alone (20 t o 28% GV for LH+DRB; P<0.05 vs FSH+DRB), and treatment with DRB did no t block GVBD in the presence of hCG (6.8 to 13.3% GV for hCG+DRB; P<0. 001 vs FSH+DRB). Inhibition of cumulus expansion by treatment with DRB occurred in the presence of either FSH or LH. Based on these results, it is suggested that DRB prevents GVBD in cultured bovine COC by inte rfering with a transcriptional event mediated primarily by FSH.