Analysis of glucose transporter mRNA levels in adipose tissue from streptozotocin (STZ)-induced diabetic rats demonstrated a specific decrease (10fold) in adipose tissue GLUT-4 mRNA with no significant effect on GLUT-1 mRNA levels. Treatment of STZ-diabetic rats with twice daily injections of insulin for 1-3 days resulted in a 16-fold increase in the relative amount of GLUT-4 mRNA to levels approximately 2-fold greater than those in control animals. However, after 7 days of insulin therapy the

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... mount of GLUT-4 mRNA decreased approximately 2-fold back to the levels in the control animals. Normalization of the STZ-induced serum hyperglycemia by phlorizin treatment, which inhibits renal tubular reabsorption of glucose, had no effect on GLUT-4 mRNA in the absence of insulin. Similar to STZ-diabetes, fasting for 48 h also reduced adipose GLUT-4 mRNA levels. Parenteral administration of insulin with glucose over 7.5 h, but not glucose alone, increased the levels of the GLUT-4 mRNA 3to 4-fold. These studies demonstrate that the relative glycemic state does not influence GLUT-4 glucose transporter mRNA expression in vivo and strongly suggests that insulin is a major factor regulating the levels of GLUT-4 mRNA in adipose tissue. (Molecular Endocrinology 4: 583-588, 1990) 1 We have employed the following abbreviations for the facilitative glucose transporters: GLUT-1 is the erythrocyte/ HepG2/rat brain glucose transporter (9, 10); GLUT-2 is the liver/islet glucose transporter having 55% sequence identity with the GLUT-1 protein (6, 8); GLUT-3 is the glucose transporter isolated from a human fetal muscle cDNA library having 64% sequence identity with the GLUT-1 protein and is expressed in most tissues (7) ; and GLUT-4 is the predominant glucose transporter expressed in adipose and muscle tissues (11 -15) having 65% amino acid sequence identity to the GLUT-1 protein. 583 Downloaded from https://academic.oup.com/mend/article-abstract/4/4/583/2714089 by guest on