GLUCOSE-ABSORPTION AND UTILIZATION BY RAT EMBRYOS

There is little doubt that glucose plays a significant nutritional rol e in early somite embryos. The high glucose utilization of anaerobic: glycolysis drops as the activity of the Kreb's cycle and terminal elec tron transport increase. Concurrently, maturation of mitochondrial cri stae and dependence on oxygen supply are taking place. The neuroepithe lium of the early somite rat embryo responds in vitro during culture b y microvilliar lengthening when exposed to glucose levels of 50 mg/dl or more. At lower glucose concentrations both in whole embryo culture and inside the closed neural tube the microvilli are shorter. Lengthen ing of the microvilli at room temperature is produced only by d-glucos e and 2-deoxyglucose, two hexoses that are absorbed and phosphorylated . Cytochalasin D which disrupts actin polymerization causes ballooning of the microvilli. A role of this microvillar elongation in degenerat ive changes seen in uncontrolled diabetes and on function of the immun e system is proposed. The amniotic cavity is one major portal of entry for glucose during the early somite embryo stage. The 7-fold increase in volume of the amniotic cavity after day 10 allows the rat embryo t o convert its axis from dorsal to ventral flexion.