Glucose absorption and utilization by rat embryos.

There is little doubt that glucose plays a significant nutritional role in early somite embryos. The high glucose utilization of anaerobic glycolysis drops as the activity of the Kreb's cycle and terminal electron transport increase. Concurrently, maturation of mitochondrial cristae and dependence on oxygen supply are taking place. The neuroepithelium of the early somite rat embryo responds in vitro during culture by 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. Lengthening of the microvilli at room temperature is produced only by d-glucose 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 degenerative changes seen in uncontrolled diabetes and on function of the immune 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 to convert its axis from dorsal to ventral flexion.