CANINE CONCEPTUS APPEARANCE AND DE-NOVO PROTEIN-SYNTHESIS IN RELATIONTO THE TIME OF IMPLANTATION

Characterization of proteins secreted by the endometrium and the conce ptus, and timing of the secretion relative to endocrine patterns, ovul ation and implantation is essential for understanding mechanisms in ma ternal recognition of pregnancy. Plasma estradiol-17 beta, progesteron e and serum LH were assayed in samples taken daily during proestrus, e strus and diestrus in 8 adult bitches. The day of the LH peak (DL 1) w as accepted as the first day on which LH concentrations exceeded the p receding day's value by 2 SD. Embryos were flushed from uteri collecte d on DL 16 to 20, and incubated with (S-35) methionine in MEM; nascent polypeptides in the medium were characterized by 2-dimensional SDS-PA GE. Some attached embryos were first observed on DL 20, and all embryo s were attached on DL 22. Major radiolabeled proteins recognized on fl uorograms were canine protein 1 (cP1) (Mr = 86,000, pI 5), cP2 (Mr = 4 2-44,000, pI 5.5-5), cP4 (Mr = 30-28,000, pI 5), cP6 (Mr = 20-25,000 p I 5.5-5) and the canine conceptus protein 7 (cCP7) (Mr = 18,000, pI 4) . All the proteins were found in samples taken from DL 19 to 20. Prote ins cP1 through cP6 were identified as produced by the embryos in this study. They were found to migrate on 2D-SDS-PAGE in a manner judged t o be identical to proteins that had been produced by the endometrium. Canine Conceptus Protein 7 was found to be secreted prior to implantat ion, only by blastocysts.