Effect of guinea-pig conceptus and its secretions on endometrial prostaglandin output

The co-culture of Day-15 guinea-pig conceptuses or Day-15 pregnant guinea-pig endometrium with Day-15 non-pregnant guinea-pig endometrium had no inhibitory effect on PGF2 alpha output from the non-pregnant endometrium. Unpurified proteins secreted by the Day-15 guinea-pig conceptuses, or these proteins purified by Blue Sepharose CL-6B and ion-exchange column chromatography also had no inhibitory effect on PGF2 alpha output from Day-15 non-pregnant guinea-pig endometrium cultured in vitro. However, following the further purification of guinea-pig conceptus secreted proteins on Sephadex G-75SF, the proteins present in fraction F3:4 inhibited PGF2 alpha output from the Day-15 non-pregnant guinea-pig endometrium during the first 6 h of culture. The major protein present in F3:4 had a molecular weight of 38.2 kDa on SDS-PAGE. Proteins present in F3:4 formed only a minor proportion of the total proteins secreted. Nevertheless, the anti-luteolytic factor secreted by the guinea-pig conceptus may be this 38.2 kDa protein, but further study is required.