Recombinant Bovine Growth Hormone Stimulates Nuclear Maturation of Bovine Oocytes In Vitro and Promotes Subsequent Embryonic Development.

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Abstract
The present study was undertaken to examine the effects of recombinant bovine growth hormone (rbGH) on nuclear and cytoplasmic maturation of bovine oocytes in vitro and subsequent embryonic development after in vitro fertilization. When cumulus-oocyte complexes (COCs) and cumulus-free oocytes were cultured in modified Medium 199 supplemented with 0, 0.1, 1, 10, 100 or 1000 ng/ml rbGH for 24 h, no cumulus expansion was observed in most COCs in the presence of any of the tested concentrations of rbGH. The efficacy of nuclear maturation of oocytes to metaphase II was promoted by rbGH only in COCs showing higher proportions at 10-1000 ng/ml (77-78%) than at 0-1 ng/ml (57-64%). When COCs were cultured in the presence or absence of 10 ng/ml rbGH for 0-9 h, the proportions of oocytes that reached prometaphase I and metaphase I after 6 and 9 h of culture, respectively, were higher in the presence (53% and 51%, respectively) than in the absence (34% and 30%, respectively) of rbGH. After in vitro maturation and fertilization, no differences were observed in the penetration rate (82-91%), pronuclear formation (27-45%) and polyspermy (23-29%) at 8 h post-insemination among cumulus-enclosed oocytes cultured in the presence of different concentrations (0-1000 ng/ml) of rbGH. When starting 8 h after insemination, the oocytes were cultured for 136 h in a chemically defined medium, 21-25% of oocytes developed to the morula stage or beyond without difference among different concentrations of rbGH during oocyte maturation. However, at 192 h post-insemination higher proportions of oocytes developed to the blastocyst stage when COCs were matured in the presence (13-15%) than in the absence (6%) of 10-1000 ng/ml rbGH. These results indicate that a stimulatory effect of rbGH on bovine oocyte maturation is dependent on the cumulus cells. Presence of rbGH in the media improved maturation rate and subsequent embryonic development to the blastocyst stage.

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