Changes in insulin-receptor mRNA levels in skeletal muscle and brown adipose tissue of weanling rats during fasting and refeeding.

Tissue-specific alterations in insulin sensitivity occur in response to fasting and refeeding, as part of the integrated adaptive mechanisms employed to adjust to major changes in nutritional status. In the present study the effects of fasting and refeeding on insulin-receptor, actin and myosin mRNA levels in skeletal muscle, and insulin-receptor and uncoupling-protein mRNA in brown adipose tissue of rats have been examined. Insulin-receptor mRNA levels increased markedly in both skeletal muscle and brown adipose tissue after a 40 h fast, the increase being greater in brown fat (8-fold) than in muscle (2-fold). On refeeding for 4 h, the insulin-receptor mRNA level in both tissues declined rapidly to control levels. An increase in insulin-receptor mRNA level was also observed in brown adipose tissue after a 16 h fast, although not in skeletal muscle. In contrast to the insulin-receptor mRNA, the level of the mRNA for the mitochondrial uncoupling protein declined markedly in brown adipose tissue during a 40 h fast. These results indicate that insulin-receptor mRNA levels are modulated in response to the alterations in nutritional status that occur during fasting and refeeding; this may reflect a nutritional influence on transcription of the receptor-protein gene.