Mouse embryos used as a bioassay to determine control of marsupial embryonic diapause

Mouse blastocysts appear to be under direct inhibition from the uterine environment, whereas no evidence of direct inhibition during diapause in the tammar wallaby has been observed. Normally developing (day 4) and quiescent mouse blastocysts were incubated for up to 12 hr in media supplemented with BSA, wallaby plasma, wallaby day 0 (day of removal of pouch young; RPY), day 5, or day 10 endometrial exudates at a concentration of 2 mg/ml of protein, and analyzed for rates of carbohydrate metabolism using fluorescence and radioisotopes. Rates of glucose uptake and lactate production by day 4 blastocysts increase after incubation with day 10 and day 5 wallaby exudates compared with rates by blastocysts incubated in BSA. Pyruvate uptake increased after 8 hr irrespective of incubation media, except for embryos incubated in day 0 exudate, which maintained levels significantly lower than BSA-incubated embryos. Quiescent mouse embryos displayed a high ATP/ADP ratio during diapause (1.06 +/- 0.24) which decreased after 4 hr incubation in all media (0.42 +/- 0.05; P < 0.01) but embryos incubated in day 0 exudate media remained at a significantly higher level than embryos incubated in BSA. These results indicate that quiescent tammar endometrial exudate is not capable of initiating diapause in mouse embryos at the concentration used, but is able to slow the rate of reactivation of quiescent blastocysts. Importantly, reactivated wallaby exudate increases mouse blastocyst glucose metabolism and lactate production. It is possible that the quiescent tammar endometrial environment has an inhibitory factor necessary to maintain diapause in the tammar blastocyst.