GLUCOSE-UTILIZATION BY COMPONENTS OF THE MOUSE CONCEPTUS DURING EARLYEMBRYOGENESIS

Mouse conceptuses were collected from female mice between day 6.5 and day 9.5 of pregnancy, dissected into their component parts and incubat ed for 2.5 h at 37 degrees C in droplets of Hepes-buffered medium cont aining 1 or 5 mmol glucose l(-1) supplemented with 0.33 mmol pyruvate l(-1) plus either 1 or 5 mmol (DL) lactate l(-1) under oil. Glucose di sappearance and lactate appearance were measured enzymatically at the end of incubation. High glucose concentration doubled utilization of t his substrate per microgram of embryonic protein, but the change in la ctate concentration had no effect on glucose turnover. Over the whole period of development studied, tissue from the ectoplacental cone exhi bited the lowest rate of glucose turnover of all tissues isolated. At day 8.5, there was little difference between yolk sac and embryonic ti ssues, but by day 9.5, the yolk sac had a higher rate of utilization o f glucose than did embryonic tissues. By this time, the embryonic tiss ues had started to show some metabolic differentiation, with head and visceral tissue exhibiting 20% higher turnover of glucose than that of body tissue. Overall, the rate of glucose utilization fell as develop ment progressed and the estimate of the relative rate of glucose utili zation on day 9.5 was half the value on day 6.5.