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

Mouse blastocysts appear to be under direct inhibition from the uterine env ironment, whereas no evidence of direct inhibition during diapause in the t ammar 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), d ay 5, or day 10 endometrial exudates at a concentration of 2 mg/ml of prote in, and analyzed for rates of carbohydrate metabolism using fluorescence an d radioisotopes. Rates of glucose uptake and lactate production by day 4 bl astocysts increase after incubation with day 10 and day 5 wallaby exudates compared with rates by blastocysts incubated in BSA. Pyruvate uptake increa sed after 8 hr irrespective of incubation media, except for embryos incubat ed in day 0 exudate, which maintained levels significantly lower than BSA-i ncubated embryos. Quiescent mouse embryos displayed a high ATP/ADP ratio du ring 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 medi a remained at a significantly higher level than embryos incubated in BSA. T hese results indicate that quiescent tammar endometrial exudate is not capa ble of initiating diapause in mouse embryos at the concentration used, but is able to slow the rate of reactivation of quiescent blastocysts. Importan tly, reactivated wallaby exudate increases mouse blastocyst glucose metabol ism and lactate production. It is possible that the quiescent tammar endome trial environment has an inhibitory factor necessary to maintain diapause i n the tammar blastocyst. J. Esp. Zool. 283:590-599, 1999. (C) 1999 Wiley-Li ss,Inc.