REACTIVATING TAMMAR WALLABY BLASTOCYSTS OXIDIZE GLUCOSE

Metabolic reactivation of the tammar blastocyst appears to be characte rized by a change in the pathway of glucose metabolism rather than an absolute increase in substrate uptake. The switch in type of metabolis m used was examined to gain information on the timing and physiology o f blastocyst reactivation. Fluorescent and radioisotope techniques wer e used sequentially to determine the activity of pathways of glucose m etabolism by individual wallaby blastocysts during diapause and 3, 4, 5, 6, 7, 8, and 10 days after removal of pouch young (RPY). Maternal e ndometrial and luteal cell metabolism and circulating hormone levels w ere measured and correlated with blastocyst activity. Observed differe nces between rates of blastocyst reactivation could be explained by va riation in the maternal response between animals. While blastocysts re covered 4 days after RPY oxidized more glucose compared with Day 0 bla stocysts (p < 0.05), rates of glycolysis did not change until Day 10. Blastocysts recovered between 4 and 10 days after RPY oxidized a signi ficantly greater percentage of the glucose taken up (p < 0.01). The re duced ATP:ADP ratio within blastocysts recovered 3 days after RPY (p < 0.05) indicates that conditions are suitable for blastocysts to under go a metabolic switch from glycolytic to oxidative metabolism of gluco se on Day 4 after RPY. The increased oxidation results in greater ATP production, which plausibly fuels the increased energy requirements of wallaby blastocysts during the early stages of reactivation.