Primate preimplantation embryo is a target for relaxin during early pregnancy

ObjectiveTo determine whether preimplantation embryos are targets for relaxin secreted from the corpus luteum of the menstrual cycle.DesignRhesus monkey oocytes obtained from females undergoing controlled ovarian hyperstimulation were inseminated, and the resulting embryos were cultured in medium with or without recombinant human relaxin (20 ng/mL) for 8 days.SettingResearch laboratory.Animal(s)Rhesus monkey.Intervention(s)Controlled ovarian stimulation to obtain oocytes for in vitro–produced embryos that were cultured with or without human recombinant relaxin.Main Outcome Measure(s)Rate of blastocyst development, percentage of blastocysts, and inner cell mass/trophectoderm cell ratio were measured on day 8 of culture. The presence of relaxin receptor (RXFP1) messenger RNA in eight-cell embryos was observed by array hybridization.Result(s)RXFP1 receptor expression was localized to the inner cell mass of blastocysts, as shown by immunohistochemistry. The percentage of embryos that developed to blastocyst and the inner cell mass/trophectoderm cell ratio was unchanged with relaxin supplementation; however, the relaxin-treated embryos developed into blastocysts significantly sooner than untreated embryos.Conclusion(s)These results are the first evidence that the preimplantation primate embryo is a target for relaxin and that the addition of relaxin to in vitro culture medium enhances rhesus monkey embryo development.