Conceptus-endometrial interactions and reproductive hormone profiles during embryonic diapause and reactivation of the blastocyst in the European roe deer (Capreolus capreolus)

Abstract: Roe deer blastocysts exhibit obligate embryonic diapause between early August and late December. The blastocyst then expands and elongates rapidly before implantation. The objective of this study was to ascertain the cues for reactivation of the diapausing blastocyst. Blood samples and reproductive tracts were collected from roe does during diapause, blastocyst expansion and subsequent implantation. Peripheral concentrations of oestradiol-17/3, progesterone and prolactin were measured by radioimmunoassay. Luteal progesterone release was determined following in vitro incubation. Conceptuses and endometrial tissue were cultured with 3H-leucine for 24 hours to measure de novo synthesis of secretory proteins. Endometrial secretory proteins were separated by two-dimensional electrophoresis. Results showed that peripheral progesterone concentrations declined by 55% just prior to expansion and did not rise until a 3-fold increase after implantation. Luteal progesterone release remained constant until expansion when it declined by 50% before increasing 2-fold at elongation and implantation. Concentrations of oestradiol-17/3 remained at a consistently low level during diapause and expansion until a 30-fold increase at elongation with concentrations remaining elevated after implantation. Plasma prolactin levels remained at basal concentrations during late diapause and then increased marginally at reactivation before decreasing again at elongation and implantation. Incorporation of radiolabel into both conceptus and endometrial secretory proteins was low during diapause, but incorporation in the conceptus increased 4¬fold at expansion and by 24-fold at the expanded trophoblast stage. Incorporation into endometrial secretoty proteins remained constant until the expanded trophoblast stage and implantation when a 2-fold increase was recorded. Furthermore, the profile of endometrial secretory proteins was constant during diapause and expansion but changed qualitatively following implantation. These data indicate that both endometrial protein synthesis and sectetion did not change during late diapause and early expansion. The increase in conceptus protein synthesis not only precedes that of the endometrium but consistently low luteal progesterone release, peripheral progesterone and oestradioi-17/J concentrations at early expansion suggests that reactivation is not in response to a maternal uterine trigger