Nutritional Regulation of Insulin-Sensitive Glucose Transporter Gene Expression in Rat Cardiac Muscle

The effects of fasting and refeeding on the levels of mRNA encoding the insulin-sensitive glucose transporter (GLUT4) in rat cardiac and skeletal muscle were investigated using solution hybridization/RNase protection assays with a rat GLUT4 antisense RNA probe. In addition, the effects of these nutritional states on GLUT1 mRNA levels in several non-insulin-sensitive tissues were examined using a GLUT1 antisense RNA probe. Fasting for 48 hr significantly decreased GLUT4 mRNA levels in heart, with levels significantly increased over control levels by 24 hr after refeeding. In contrast, GLUT4 mRNA levels in skeletal muscle increased with fasting and returned to control levels with refeeding. No significant changes in GLUT1 mRNA were seen after fasting and refeeding in several non-insulin-sensitive tissues studied. These results suggest that altered GLUT4 gene expression is observed in different nutritional (insulin) states in insulin-sensitive tissues, and suggests a potential role for insulin in mediating these changes in gene expression.