Human muscle glycogen resynthesis after exercise: insulin-dependent and -independent phases.
To study the effects of glycogen depletion and insulin concentration on glycogen synthesis, gastrocnemius glycogen was measured with 13C-nuclear magnetic resonance at 4.7 T after exercise. Subjects performed single-leg toe raises to deplete gastrocnemius glycogen to 75, 50, or 25% of resting concentration (protocol I). Insulin dependence of glycogen synthesis was assessed after depletion to 25% with (protocol II) and without (protocol III) infusion of somatostatin to inhibit insulin secretion. After depletion to 75 and 50%, glycogen resynthesis rates were similar (2.4 +/- 0.7 and 2.8 +/- 0.6 mM/h, respectively). When glycogen was depleted to 25% (< 30 mM), the resynthesis rate was significantly 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 affected by low insulin (24 +/- 4 mM/h, protocol vs. 19 +/- 3 mM/h, protocol III), whereas at > 35 mM glycogen, synthesis ceased without insulin (-0.07 +/- 0.19 mM/h, protocol II). After depletion to 25% (protocol III), 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 plasma constituents did not significantly change. We conclude that after depletion to < 30 mM initial glycogen resynthesis is insulin independent and glycogen dependent, which suggests local control.
Price
T B
TB
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut.
Rothman
D L
DL
Taylor
R
R
Avison
M J
MJ
Shulman
G I
GI
Shulman
R G
RG
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005260:Female; D006003:Glycogen / Q000096:biosynthesis*; D006801:Humans; D007328:Insulin / Q000502:physiology*; D007700:Kinetics; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009132:Muscles / Q000378:metabolism*; D013004:Somatostatin / Q000494:pharmacology
D001786:Blood Glucose; D007328:Insulin; D007773:Lactates; D019344:Lactic Acid; D013004:Somatostatin; D006003:Glycogen