EFFECTS OF DEXAMETHASONE IN-VIVO AND IN-VITRO ON HEXOSE-TRANSPORT IN BRAIN MICROVASCULATURE

Glucocorticoids induce hyperinsulinemia, hyperglycemia, and depress gl ucose transport by aortic endothelium. High glucocorticoid doses are u sed for many diseases, but with unknown effects on brain glucose trans port or metabolism. This study tested the hypothesis that glucocortico ids affect glucose transport or metabolism by brain microvascular endo thelium. Male rats received dexamethasone (DEX) sc with sucrose feedin g for up to seven days. Cerebral microvessels from rats treated with D EX/sucrose demonstrated increased GLUT1 and brain glucose extraction c ompared to controls. Glucose transport in vivo correlated with hyperin sulinemia. Pre-treatment with low doses of streptozotocin blunted hype rinsulinemia and prevented increased glucose extraction induced by DEX . in contrast, isolated brain microvessels exposed to DEX in vitro dem onstrated suppression of 2-deoxyglucose uptake and glucose oxidation. We conclude that DEX/sucrose treatment in vivo increases blood-brain g lucose transport in a manner that requires the effects of chronic hype rinsulinemia. These effects override any direct inhibitory effects of either hyperglycemia or DEX.