Sj. Vannucci et al., ALTERED EXPRESSION OF GLUT-1 AND GLUT-3 GLUCOSE TRANSPORTERS IN NEUROHYPOPHYSIS OF WATER-DEPRIVED OR DIABETIC RATS, American journal of physiology: endocrinology and metabolism, 30(4), 1994, pp. 50000605-50000611
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.