Lean and obese Zucker rats exhibit different patterns of p70s6 kinase regulation in the tibialis anterior muscle in response to high-force muscle contraction.

Increased phosphorylation of the 70-kDa ribosomal S6 kinase (p70S6k) signaling is strongly correlated with the degree of muscle adaptation following exercise. Herein we compare the phosphorylation of p70S6k, Akt, and mammalian target of rapamycin (mTOR) in the tibialis anterior (TA) muscles of lean and obese Zucker rats following a bout of eccentric exercise. Exercise increased p70S6k (Thr389) phosphorylation immediately after (33.3+/-7.2%) and during [1 h (24.0+/-14.9%) and 3 h (24.6+/-11.3%)] recovery in the lean TA and at 3 h (33.5+/-8.0%) in the obese TA Zucker rats. mTOR (Ser2448) phosphorylation was elevated in the lean TA immediately after exercise (96.5+/-40.3%) but remained unaltered in the obese TA. Exercise increased Akt (Thr308) and Akt (Ser473) phosphorylation in the lean but not the obese TA. These results suggest that insulin resistance is associated with alterations in the ability of muscle to activate p70S6k signaling following an acute bout of exercise.