Follicle size-dependent induction of prostaglandin G/H synthase-2 during superovulation in cattle.
Under physiological conditions, prostaglandin G/H synthase-2 (PGHS-2) is induced in bovine preovulatory follicles by the endogenous surge of gonadotropins. To characterize the pattern of follicular PGHS-2 expression during superovulation in cattle, heifers were treated with exogenous FSH and ovulation was induced with hCG. Animals were ovariectomized 0, 18, and 24 h post-hCG, and extracts of follicles > or = 6 mm were analyzed by Western blotting. Follicular fluid concentrations of prostaglandin (PG) E2, PGF2alpha, progesterone, and estradiol-17beta were determined by RIAs, and the morphology of the cumulus oocyte complex was examined. Results showed that PGHS-2 protein was absent in all follicles isolated at 0 h post-hCG (n = 119) and in small follicles (6 to < 8 mm) isolated between 0 and 24 h post-hCG (n = 27 follicles). In contrast, 12.3% of medium (8 to < 10 mm) and 43.7% of large (> or = 10 mm) follicles were PGHS-2-positive at 18 h post-hCG, and these percentages rose at 24 h to 45.9% and 91.0% in medium and large follicles, respectively (p < 0.05). Follicular fluid concentrations of PGE2 and PGF2alpha were low in follicles isolated at 0 h and increased only in PGHS-2-positive follicles isolated 24 h post-hCG (p < 0.05). Concentrations of progesterone and estradiol-17beta at 0 h were 28.2 +/- 5.8 and 291.8 +/- 13.0 ng/ml, respectively, and a shift from estradiol-17beta to progesterone dominance (luteinization) occurred at 24 h post-hCG only in PGHS-2-positive follicles. Also, expansion of the cumulus oocyte complex was detected at 24 h post-hCG only in PGHS-2-positive follicles. Lack of PGHS-2 induction in follicles of ovulatory size (> 8 mm) was associated with an apparent failure to respond to hCG (absence of luteinization and cumulus expansion). Collectively, these results demonstrate the presence of a time- and follicle size-dependent induction of PGHS-2 in bovine follicles during superovulatory treatment and suggest that PGHS-2 expression can be used as a marker for follicular commitment to ovulation during ovarian hyperstimulation protocols.
Liu
J
J
Centre de recherche en reproduction animale, Département de biomédecine vétérinaire, Faculté de médecine vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec, Canada.
Sirois
J
J
D000818:Animals; D002417:Cattle; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D015237:Dinoprost / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D004790:Enzyme Induction; D004958:Estradiol / Q000378:metabolism; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D015571:Follicular Fluid / Q000378:metabolism; D007700:Kinetics; D006080:Ovarian Follicle / Q000033:anatomy & histology* / Q000502:physiology; D010052:Ovariectomy; D011374:Progesterone / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis*; D013480:Superovulation
D006063:Chorionic Gonadotropin; D011374:Progesterone; D004958:Estradiol; D005640:Follicle Stimulating Hormone; D015237:Dinoprost; D011451:Prostaglandin-Endoperoxide Synthases; D015232:Dinoprostone