HUMAN MUSCLE GLYCOGEN RESYNTHESIS AFTER EXERCISE - INSULIN-DEPENDENT AND INSULIN-INDEPENDENT PHASES

To study the effects of glycogen depletion and insulin concentration o n glycogen synthesis, gastrocnemius glycogen was measured with C-13-nu clear magnetic resonance at 4.7 T after exercise. Subjects performed s ingle-leg toe raises to deplete gastrocnemius glycogen to 75, 50, or 2 5% of resting concentration (protocol I). Insulin dependence of glycog en synthesis was assessed after depletion to 25% with (protocol II) an d without (protocol III) infusion of somatostatin to inhibit insulin s ecretion. After depletion to 75 and 50%, glycogen resynthesis rates we re similar (2.4 +/- 0.7 and 2.8 +/- 0.6 mM/h, respectively). When glyc ogen was depleted to 25% (<30 mM), the resynthesis rate was significan tly higher (P < 0.02) at 33 +/- 7 mM/h, and it declined to 3.5 +/- 0.9 mM/h at >35 mM glycogen. At <35 mM glycogen, synthesis was not affect ed by low insulin (24 +/- 4 mM/h, protocol II vs. 19 +/- 3 mM/h, proto col III), whereas at >35 mM glycogen, synthesis ceased without insulin (-0.07 +/- 0.19 mM/h, protocol In. After depletion to 25% (protocol I II), plasma lactate transiently increased (0.81 mM at rest, 1.82 mM 0 h after exercise, and 0.76 mM 2 h after exercise), whereas other plasm a constituents did not significantly change. We conclude that after de pletion to <30 mM initial glycogen resynthesis is insulin independent and glycogen dependent, which suggests local control.