Gonadotropin-mediated dynamic changes in cytoplasmic and nuclear maturation in vitro: an animal model

Abstract

OBJECTIVE: A high level of Gn in follicular fluids may contribute to ovarian hyper-stimulation in ART. The goal of this study was to determine whether there is a dose response effect on oocyte maturation in an animal model.DESIGN: Prospective experimental study.MATERIALS AND METHODS: Experiments were designed according to current popular stimulation protocols in ART, i.e. Bravelle only (B), combination of B and Menopur (B+M) or Repronex (B+R). Bovine oocytes were matured in media supplemented with 75, 750, 7500 or 75 000 mIU/ml Gn or combination of Gn in vitro for 24 h. The control group (NL) had no Gn in the media. Nuclear maturation status, spindle and chromosomal configurations, dynamic changes of the cortical granules (CGs) and mitochondria were evaluated by immunostaining and confocal laser scanning microscope.RESULTS: The nuclear maturation rates were 59.48%, 52.60%, 58.33% and 41.01% in B group, 61.11%, 58.52%, 50.00% and 33.57% in B+M group, 55.26%, 53.97%, 51.47% and 30.83% in B+R group, respectively. During in vitro maturation (IVM) of bovine oocytes, mitochondria formed larger clusters and migrated more centrally and CGs dispersed in cytoplasmic. Except 75000 mIU/ml B subgroup, supplement of different dose of Gn did not influence the migrations of mitochondria and CGs. There were no significant differences between 75, 750, 7500 mIU/ml groups and NL in normal spindle and chromosomal configurations. However, in 75000 mIU/ml groups, only 19.05% (B), 11.76% (B+M) and 0 (B+R) of the MII oocytes had normal spindles.CONCLUSION: Results demonstrated that low to moderate dose of Gn could improve nuclear maturation. However, extremely high dose of Gn had no beneficial effects on nuclear maturation. Although the redistributions of mitochondria and cortical granules (CG) were not altered in a dose-response manner, high dose of Gn did induce spindle and chromosomal abnormalities. Our study highlights the importance of judicious use of Gn and can be applied to clinical stimulation protocols to reduce the potential risks. OBJECTIVE: A high level of Gn in follicular fluids may contribute to ovarian hyper-stimulation in ART. The goal of this study was to determine whether there is a dose response effect on oocyte maturation in an animal model. DESIGN: Prospective experimental study. MATERIALS AND METHODS: Experiments were designed according to current popular stimulation protocols in ART, i.e. Bravelle only (B), combination of B and Menopur (B+M) or Repronex (B+R). Bovine oocytes were matured in media supplemented with 75, 750, 7500 or 75 000 mIU/ml Gn or combination of Gn in vitro for 24 h. The control group (NL) had no Gn in the media. Nuclear maturation status, spindle and chromosomal configurations, dynamic changes of the cortical granules (CGs) and mitochondria were evaluated by immunostaining and confocal laser scanning microscope. RESULTS: The nuclear maturation rates were 59.48%, 52.60%, 58.33% and 41.01% in B group, 61.11%, 58.52%, 50.00% and 33.57% in B+M group, 55.26%, 53.97%, 51.47% and 30.83% in B+R group, respectively. During in vitro maturation (IVM) of bovine oocytes, mitochondria formed larger clusters and migrated more centrally and CGs dispersed in cytoplasmic. Except 75000 mIU/ml B subgroup, supplement of different dose of Gn did not influence the migrations of mitochondria and CGs. There were no significant differences between 75, 750, 7500 mIU/ml groups and NL in normal spindle and chromosomal configurations. However, in 75000 mIU/ml groups, only 19.05% (B), 11.76% (B+M) and 0 (B+R) of the MII oocytes had normal spindles. CONCLUSION: Results demonstrated that low to moderate dose of Gn could improve nuclear maturation. However, extremely high dose of Gn had no beneficial effects on nuclear maturation. Although the redistributions of mitochondria and cortical granules (CG) were not altered in a dose-response manner, high dose of Gn did induce spindle and chromosomal abnormalities. Our study highlights the importance of judicious use of Gn and can be applied to clinical stimulation protocols to reduce the potential risks.