Action of hormones on germinal vesicle breakdown in frog (Rana pipiens) oocytes

Abstract

The mechanism of pituitary gland and progesterone induced germinal vesicle breakdown (GVBD) was investigated in isolated ovarian follicles or oocytes of Rana pipiens. The effects of removing follicular tissue and the metabolic inhibitors, puromycin and actinomycin D, on oocyte responsiveness to the hormones were of Rana pipiens. The effects of removing follicular tissue and the metabolic inhib of protein synthesis, blocked both pituitary and steroid induced GVBD. Timed inhibition studies indicated that protein synthesis was completed at a time approximately midway between the time of progesterone addition and the initiation of GVBD. Only a short exposure of oocytes (5–15 minutes) to progesterone was sufficient to initiate GVBD. Puromycin did not act by preventing the uptake of steroids by the ovarian follicles; however, it caused irreversible effects to oocytes when present in the incubation medium for more than 4 hours. Removal of the follicular tissue from oocytes did not impair oocyte GVBD following exposure to progesterone; however, pituitary induced GVB was inhibited in approximately 50% of the animals utilized. Addition of actinomycin D (100 μg/15 ml) prevented pituitary, but not steroid induced GVBD when added to the incubation medium at the time of hormone administration. Actinomycin D was increasingly ineffective in preventing GVBD when its addition to oocytes was delayed following exposure to pituitary tissue. These data suggest that pituitary and steroid induced GVBD are mediated by a common mechanism concerned with protein synthesis. The differential inhibition of pituitary induced GVBD with actinomycin D suggests the presence of a pituritary stimulated intermediary process prior to the initiation of protein synthesis. The ovarian follicular tissue appears to be partially responsible for mediating the action of the pituitary gland.