In vitro induction of ovulation and oocyte maturation in Rana pipiens ovarian follicles: effects of steroidal and nonsteroidal hormones.

Abstract

AbstractIndividual ovarian follicles of Rana pipiens respond to hormonal stimuli in vitro. The relative effectiveness of progesterone and gonadotrophic hormones in initiating ovulation and oocyte maturation were compared. Maturation of oocytes (>99%) with limited concomitant ovulation resulted following treatment of follicles with progesterone. Frog pituitary tissue was less effective than progesterone in stimulating maturation, but was more effective in producing ovulation. Neither ovulation nor maturation was stimulated in response to the mammalian gonadotrophic hormones (FSH, LTH, PMS, HCG) or mammalian growth hormone. Mammalian LH produced both ovulation and maturation; furthermore, no synergistic interaction with FSH was observed. Maturation did not occur in response to the gonadotrophic hormones without a concomitant, but not necessarily equivalent, induction of ovulation. Follicular responsiveness, particularly to gonadotrophic hormones, was affected by animal and seasonal variations. Structural changes (follicular membrane detachment from the oocyte) were observed in unovulated follicles treated with hormones. The structural alterations were closely correlated with the induction of oocyte maturation. These observations suggest that (1) the intrafollicular events leading to ovulation and maturation are not equally sensitive to pituitary and progesterone stimulation, (2) maturation and ovulation activities of gonadotrophins are probably inseparable, (3) responsiveness of follicles to specific gonadotrophins is not related to only their FSH or LH activity. These data are consistent with the hypothesis that gonadotrophins act indirectly via the follicular tissues to initiate the processes of ovulation and maturation.