Desensitization to follicle-stimulating hormone in cumulus cells is coincident with hormone induction of oocyte maturation in the rat follicle

Abstract

The objective of the present studies was to assess whether hormone induction of oocyte maturation in isolated intact follicles may be linked to desensitization of follicle-stimulating hormone (FSH) in the oocyte-cumulus complex (OCC). Incubation of follicles with chorionic gonadotropin (hCG), FSH or epidermal growth factor (EGF) produced a marked inhibition of FSH-dependent cyclic AMP accumulation in OCC with a time-course coincident with the onset of germinal vesicle breakdown (GVBD). These effects were evident within 3 h for both hCG and FSH, but with EGF a reduced response to FSH was seen within 1 h of treatment followed by an increase in GVBD. In contrast, no inhibition of cyclic AMP accumulation was seen in response to cholera toxin, forskolin or LH in OCC derived from follicles incubated with hCG for 3 h. The time-course for induction of oocyte maturation by incubation of the intact follicle with hCG was also coincident with production of prostaglandin (PG) F 2α, an indirect marker of cyclooxygenase induction. No effect on metabolic coupling between the oocyte and cumulus cells was seen until 9 h after hCG treatment. Retinoic acid caused a marked decrease in metabolic coupling between the oocyte and cumulus cells but inhibited oocyte maturation both in denuded oocytes and OCC. Since FSH desensitization in OCC, the resumption of meiosis, and production of arachidonic acid-derived products were coincident, it is suggested that abrogation of FSH action in cumulus cells by the ovulatory surge of gonadotropins may initiate oocyte maturation.