Possible involvement of insulin-like growth factor-I in mediating the stimulatory effect of recombinant bovine growth hormone on maturation of bovine oocytes in vitro.

摘要

When cumulus-oocyte complexes (COCs) or cumulus-free oocytes were cultured in modified medium 199 supplemented with 0-100 ng/ml recombinant human insulin-like growth factor-I (rhIGF-I), the proportion of COCs with slight cumulus expansion was increased with increasing concentration of rhIGF-I after 12 and 24 h of culture. Nuclear maturation of oocytes to the metaphase II (M-II) stage was promoted by rhIGF-I only in COCs, with higher proportions of M-II oocytes at 10-100 ng/ml than at 0-1 ng/ml after 24 h of culture. When COCs were cultured in the presence of 100 ng/ml rhIGF-I or 10 ng/ml recombinant bovine growth hormone (rbGH) and/or anti-IGF-I antibody for 24 h, the proportion of oocytes reaching the M-II stage was higher with rhIGF-I (73?%) orrbGH (74?%) than in the absence of these additives (54?%), in antibody alone (54?%), or with IGF-I or rbGH in combination with antibody (54? to 58?%). The inhibition of the stimulatory effects of rbGH on nuclear maturation by antibody was dose-dependent. After in vitro maturation and fertilization, no differences were observed in the penetration rate (75?to 77?%), pronuclear formation (56? to 64?0%) and polyspermy (28? to 36?%) at 8 h post-insemination among cumulus enclosed oocytes culturedin the presence of different additives. When the oocytes were cultured in a chemically defined medium starting from 8 h after insemination, 20? to 26?% of oocytes developed to the morula stage or later 144 h post-insemination without differences amongthe different additives during maturation. However, at 192 h post-insemination, higher proportions of oocytes developed to the blastocyst stage when COCs were matured in the presence of rhIGF-I (16?%) or rbGH (15?%) than in the absence of the additives (4?%) or when IGF-I or rbGH was combined with antibody (4? to 5?%). These results suggest that the stimulatory effects of rbGH on bovine oocyte maturation may not be direct, but mediated by IGF-I probably produced by the cumulus cells.