Direct ovarian effect of growth hormone in the rabbit

PROBLEM: This study was undertaken to assess whether growth hormone (GH) can stimulate follicle growth and ovarian steroidogenesis via putative GH receptors. METHOD: In vitro perfused rabbit ovary. RESULTS: Ovulation occurred in neither the control ovaries nor experimental ovaries treated with 100 ng/ml of GH, whereas all ovaries exposed to 50 IU of human chorionic gonadotropin (hCG) ovulated. The addition of GH to the perfusate significantly stimulated the follicle growth in the absence of gonadotropin. The percent change in follicle diameter in GH-treated ovaries did not differ significantly from that in hCG-treated ovaries. Exposure to GH significantly stimulated the meiotic maturation in the follicular oocytes, as compared with the contralateral control ovaries. Although the concentration of progesterone in the perfusate did not differ significantly between GH-treated and control ovaries, GH stimulated estradiol production by the perfused rabbit ovaries. Rabbit ovary membranes exhibited high affinity binding sites of hGH (Kd = 6.1 × 10−9M). CONCLUSION: GH acts on the rabbit ovary to stimulate the follicle growth, oocyte maturation, and ovarian estradiol production by interacting with the specific receptors located in ovarian plasma membranes.