Gonadotropin Effects on Chromosomal Normality of Hamster Preimplantation Embryos1

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Abstract
Induction of ovulation with pregnant mare's serum (PMS) and the timing of human chorionic gonadotropin (hCG) injection on chromosomal normality were examined in preimplantation hamster embryos. Two separate experimental trials were done. The first compared superovulation (SO, PMS on Day 1 of the cycle followed by hCG on Day 4) to natural ovulation. Natural mating was used. In the second series of trials, precocious superovulation (PSO, PMS on Day 1 followed by hCG on Day 3) was used. Since there is poor sperm transport in PSO females, direct uterine artificial insemination (AI) was used to achieve fertilization. The control animals in the second series of trials were naturally ovulating females subjected to the artificial insemination procedure. Of 785 embryos analyzed in the SO group, 9 (1.1%) were aneuploid (5 hyperploidy and 4 hypoploidy) and 8 (1.0%) showed triploidy. In the PSO group, artificial insemination resulted in a normal development rate of 85.5% up to the 2-cell stage. A total of 2.6% karyotypically abnormal embryos, consisting of 5 (1.1%) aneuploid and 7 (1.5%) polyploid, were found among 460 embryos examined in PSO females. No significant difference in the incidence of chromosomal abnormalities was observed between the stages of development. The overall incidence of chromosomal imbalance in hormonally treated females was not significantly different from that in controls (2.2% in SO cycles vs. 1.2% in natural cycles, 2.6% in PSO with AI vs. 2.4% in natural cycles with AI). These results indicate that PMS-hCG treatment has no adverse effect on the chromosomal integrity of hamster preimplantation embryos.