ALTERED EXPRESSION OF GLUT-1 AND GLUT-3 GLUCOSE TRANSPORTERS IN NEUROHYPOPHYSIS OF WATER-DEPRIVED OR DIABETIC RATS

Progressive dehydration due to water deprivation and streptozotocin di abetes both produce increased activity of the hypothalamoneurohypaphys ial system and enhanced vasopressin secretion. To determine whether en hanced metabolic acitivity affects glucose transporter protein express ion, this study examined the effect of these conditions on 45-kDa GLUT -1 and the neuronal glucose transporter, GLUT-3, which mediate glucose transport in the rat neurohypophysis. Progressive water deprivation i ncreased hematocrit, plasma electrolytes Na+ and Cl-, and vasopressin over 3 days, relative to the severity of dehydration. Plasma vasopress in increased threefold by 24 h, reaching 4.5-fold by 72 h. These chang es were reflected in a 56 and 75% decrease in neurohypophysial vasopre ssin content by 48 and 72 h, respectively. Significant changes in gluc ose transporters were also observed at 48 and 72 h, with GLUT-1 increa sing by 18 and 44% and GLUT-3 increasing by 42 and 55%, respectively. Streptozotocin-induced diabetes produced increases in hematocrit, plas ma Cl-, and vasopressin, although the magnitude of these changes was l ess than with dehydration. There was a twofold increase in plasma vaso pressin by 3 days, commensurate with the onset of overt diabetes, and a threefold increase by 2 wk. These changes were reflected in a 30 and 40% decline in neural lobe vasopressin content, respectively. Despite the difference in the magnitude of hormone response, GLUT-3 increased by the same amount (53%) as in dehydration. GLUT-1, however, was decr eased 16% by 3 days and 25% by 1 and 2 wk of diabetes. Although the op posite effects on GLUT-1 may relate to differences in circulating insu lin or glucose, this study is the first demonstration of increased exp ression of GLUT-3 in response to a common hypothalamic signal in these two conditions.