| Research Abstract |
To examine the effects of growth hormone(GH) on cell proliferation and cell differentiation in ovaries, the deoxyribonucleic acid(DNA) polymerase activities, DNA content, somatomedin C/insulin-like growth factor 1(IGF-1) levels, epidermal growth factor(EGF) levels, renin activities and steroid concentrations were determined in vitro and in vivo in rat ovaries. Ovine GH significantly enhanced the DNA polymerase alpha (a replicative enzyme for DNA synthesis) activity in ovaries, incubated in vitro, of 10 IU pregnant mare's serum gonadotropin(PMS)-treated hypophysectomized rats, estrogen-treated immature hypophysectomized rats and untreated hypophysectomized immature rats. In contrast, the DNA polymerase beta (a repair enzyme for DNA ) activity, DNA content, IGF-1 level, renin (prorenin) activity and EGF levels showed no significant changes. Medium concentrations of estradiol-17 beta and progesterone, and tissue cyclic AMP levels were also significantly increased in vitro by GH in growing and preovulatory follicles. The administration of GH to immature hypophysectomized rats in vivo increased the DNA polymerase alpha, but not beta, activity, DNA content and IGF-1 levels. The immunocytochemical localization by the peroxidase-labelled antibody technique showed the existence of GH receptors within the granulosa cells and demonstrated steroidogenesis stimulated by GH. These results suggest that GH stimulates the induction of DNA polymerase alpha activity in conjunction with DNA synthesis and steroidogenesis through GH-mediated events independent of IGF-1 or via an intraovarian mediator IGF-1 during cell proliferation and cell differentiation in the ovaries of immature rats.
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