STEROID-SYNTHESIS BY EQUINE CONCEPTUSES BETWEEN DAYS 7 AND 14 AND ENDOMETRIAL STEROID-METABOLISM

The objective of this study was to determine if changes in steroid syn thesis occurred in the horse blastocyst about the time of maternal rec ognition of pregnancy. Embryos collected between days 7.5 and 14.5 wer e incubated for 8 hr in vitro in HAM's F10 containing radiolabelled pr egnenolone. The steroid metabolites in the incubation medium were sepa rated by reverse phase HPLC and the major peaks expressed as a percent age of total metabolites. It was found that there were no major change s in the profile of metabolites throughout the period of study, althou gh there was increased conversion as the conceptuses developed. It was found that the major metabolite produced was 17alpha-hydroxyprogester one and not estradiol as expected. A second experiment was conducted t o determine if 17alpha-hydroxyprogesterone was metabolized by endometr ial tissue. Endometrial biopsies from anestrous mares and from pregnan t and nonpregnant mares at day 11 were incubated with radiolabelled 17 alpha-hydroxyprogesterone, progesterone or pregnenolone. The 17alpha-h ydroxyprogesterone, but not progesterone nor pregnenolone, was convert ed to a more polar metabolite in all groups. Production of this metabo lite was significant greater in the anestrous mares. This metabolite h as not been unidentified conclusively. Thus, results of this study sho w that 17alpha-hydroxyprogesterone is the major steroid synthesized by the equine blastocyst and that this steroid is further metabolized to an unidentified steroid by the endometrium. These steroids could play a role in conceptus development or maternal recognition of pregnancy.