Effects of age on in su un-stimulat e d rates of protein synthesis after resistance exercise in rats

This study examined whether or not insulin elevates rates of protein synthesis (Pro Syn) in muscle following 4 days of resistance exercise in young (4-mo), middle-aged (12-mo) and old (32-mo) rats. Male rats performed acute resistance exercise (ACUTE; n=6 each age group) or exercised with no weight over the scapula (NONEX; n =6 each age group). Pro Syn were assessed in muscles 16 h affer the last bout of exercise using a bilateral hindlimb perfusion (radiolabelled phenylalanine incorporated into muscle protein). After a 15 min washout one hindlimb received a perfusion medium that contained rat insulin (6.25 ng ml^-1), while the medium for the other limb did not. Pro Syn in soleus and gastrocnemius (GAST) with insulin supplementation were significantly higher fp<0.05) within all age groups following resistance exercise vs. ACUTE without insulin or NONEX with or without insulin. Pro Syn in CAST were significantly higher for old NONEX vs. voung NONEX (68 t b vs. 4S ±5 nmol F incorporated g^-1 h^-1 . respectively; p>0.()5) but not middleaged NONEX (51 ±3 . Translational efficiency for GAST supplemented with insulin was significantly greater in ACUTE than ACUTE without insulin or NONEX with or without insulin across age groups (p<0.05). Following resistance exercise, insulin increased Pro Syn in both soleus and CAST regardless of age, and it appeared that this insulin-mediated elevation mav have occurred at the level of translation.