PRODUCTION OF FREE ESTROGENS AND ESTROGEN CONJUGATES BY THE PREIMPLANTATION EQUINE EMBRYO

In vitro production of free estrogens and estrogen conjugates by intac t Day 12.5, 13.5 and 14.5 equine embryos was measured at 2-h intervals over a 24-h culture period. Production of free estrogens was higher f or Day 14.5 than Day 12.5 embryos. Differences in production of conjug ated estrogens were not significant, but a trend toward increased prod uction with increased age of embryo was apparent. No trend toward incr eased free and conjugated estrogen production per cell was observed wi th age. Embryo diameter and number of cells increased with age but var ied considerably within groups. The amount of free and conjugated estr ogens measured in blastocoelic fluid did not decrease over the 24-h cu lture period, suggesting that estrogens detected in culture medium wer e produced by the embryo and not the result of leakage of maternal est rogen from the blastocoele. The results of this study support previous results that estrogen production increases with development of equine embryos. This increase in estrogen production appears to be more clos ely associated with the diameter of the embryo, and hence its number o f cells, than with increased intracellular steroidogenic activity. (C) 1997 by Elsevier Science Inc.