Effect of aging and obesity on insulin responsiveness and GLUT-4 glucose transporter content in skeletal muscle of Fischer 344 x Brown Norway rats

This study investigated the metabolic changes with age in the Fischer 344 x Brown Norway rat and its suitability as an animal model of postmaturationa l insulin resistance. Specifically, we determined whether an age-associated decrease in glucose disposal is associated with diminished whole body insu lin responsiveness and/or a decrease in glucose transporter (GLUT-4) protei n and mRNA content in medial gastrocnemius muscle of male Fischer 344 x Bro wn Norway rats of ages 8, 18, and 28 months. Fasting plasma glucose was unc hanged with age. There was a significant age effect on visceral adiposity, fasting plasma insulin levels, insulin responsiveness, and GLUT-4 protein c ontent. Insulin responsiveness and GLUT-4 protein were lower in the 18-mont h-old rats than in the 8-month-old rats. The findings of age-associated inc reases in visceral adiposity and insulin resistance, and decreases in GLUT- 4 in the Fisher 344 x Brown Norway rat, suggest that this rat strain may be an appropriate model for studying the effects of aging on glucose homeosta sis.