Proteins synthesized and secreted by the guinea-pig conceptus during early pregnancy in relation to corpus luteal maintenance.

Guinea-pig conceptuses obtained on Day 15 of pregnancy were cultured for 24 h in the presence of [3H]leucine. Proteins present in the culture medium were purified by dialysis, desalted, and subjected to analysis by gel filtration chromatography, ion-exchange chromatography, and polyacrylamide gel electrophoresis. The major non-radioactive protein present co-chromatographed with serum albumin. Fresh protein synthesis occurred as indicated by the incorporation of [3H]leucine, and the proteins produced were acidic in nature. Many radioactive proteins in relatively similar amounts were produced, with protein of molecular weights 28.8 and 98.2 kDa (as determined on Sephacryl S-300HR) and of molecular weights 8.4 and 14.7 kDa (as determined on Sephadex G-75SF) being synthesized in marginally greater quantities. Consequently, from the profile of proteins synthesized and secreted, no obvious candidate emerged as the anti-luteolytic factor synthesized and secreted by the guinea-pig conceptus during early pregnancy which inhibits endometrial PGF2 alpha synthesis and maintains corpus luteal function.