Brief dietary restriction increases skeletal muscle glucose transport in old Fischer 344 rats

The primary purpose of this study was to determine the impact of brief dietary restriction (DR;5 or 20 days) on skeletal muscle glucose transport activity (GTA) of 24-month-old female Fischer 344 rats. Basal GTA of isolated epitrochlearis muscles was unaffected by DR. Insulin-stimulated GTA was significantly increased by DR only at 20 days (+51%). We also assessed the influence of DR on energy sources (blood-borne and stored). An similar to 20% decline in glycemia occurred in each DR group, but plasma-free fatty acid and beta-hydroxybutyrate concentrations were unaffected. Plasma insulin was reduced by 50% after 20 days. Hepatic glycogen was rapidly mobilized (-69% at 5 days:-83% at 20 days). The depletion of visceral adipose stores was slower (no significant decline at 5 days: -30% at 20 days), but the eventual reduction accounts for a significant amount of energy. The results demonstrate that muscle from old rats can rapidly upregulate GTA in response to brief DR. The relative magnitude of this increase represents a substantial portion of the increases previously observed after prolonged DR.