DIFFERENTIAL-EFFECTS OF GONADOTROPIN AND ORTHOVANADATE ON OOCYTE MATURATION, OVULATION, AND PROSTAGLANDIN SYNTHESIS BY RANA OVARIAN FOLLICLES IN-VITRO

Effects of gonadotropin and sodium orthovanadate on oocyte maturation, ovulation, prostaglandin, and progesterone synthesis were examined du ring in vitro culture of Rana ovarian follicles obtained from hibernat ing animals. Frog pituitary homogenates (FPH, 0.05 gland/ml) effective ly induced oocyte maturation (germinal vesicle breakdown, GVBD) and ov ulation (>90%) in ovarian follicles obtained in mid-hibernation (mid-D ecember through late January). In contrast, orthovanadate induced a li mited amount (<45%) of ovulation of some oocytes without concomitant i nduction of maturation during mid-hibernation. In late hibernation (Fe bruary to early March), considerable spontaneous maturation and ovulat ion occurred in cultured ovarian follicles. During this period both FP H (0.0005-0.05 gland/ml) or orthovanadate (0.01-1 mM) treatment marked ly increased the incidence of ovulation and accelerated the onset of o vulation in a dose dependent manner. When examined after 12 h of cultu re, few (<5%) oocytes ovulated in response to orthovanadate had underg one GVBD whereas most (>90%) of those ovulated in response to FPH had matured. However, the majority of oocytes ovulated (72%) within 6 h of exposure to FPH had intact GVs, indicating that GVBD is also not a pr erequisite for ovulation induction in response to FPH. Orthovanadate s timulated PGF(2 alpha) in a dose dependent manner but failed to stimul ate progesterone production whereas FPH stimulated secretion of both P GF(2 alpha) and progesterone. The amount and time course of PGF(2 alph a) secretion in response to orthovanadate were similar to results prod uced with FPH stimulation. Treatment of PGF(2 alpha) to follicles obta ined in late hibernation also accelerated the ovulation of the oocytes . Taken together, the data suggest that orthovanadate enhanced ovulati on of immature oocytes was mediated via enhanced PGF(2 alpha) producti on and that oocyte maturation is not essential or prerequisite for in vitro oocyte ovulation in Rana. (C) 1997 Wiley-Liss, Inc.