DETERMINANTS OF INSULIN-STIMULATED SKELETAL-MUSCLE GLYCOGEN-METABOLISM IN MAN

To examine factors which influence skeletal muscle glycogen synthesis in man, we related insulin sensitivity measured by euglycaemic insulin clamp in 43 healthy males to muscle glycogen synthase (GS) activity, GS protein content (Western blot), glycogen concentrations and fibre c omposition. Insulin increased muscle glycogen content (P < 0.05) and t he change in glycogen content correlated with the GS protein content ( r = 0.90, P = 0.01). GS protein concentration correlated inversely wit h age (r = -0.69, P = 0.04). Non-oxidative glucose disposal was invers ely related to per cent type 2B fibres (r = -0.52, P < 0.05). The infl uence of age on these relationships was separately studied in young (n = 12, age = 26 +/- 2 years) and elderly (n = 15, age = 56 +/- 2 years ) males. Insulin increased GS activity significantly only in young sub jects (from 17.8 +/- 3.0 to 25.3 +/- 3.2 nmol mg protein(-1) min(-1) P = 0.015). GS activity and nonoxidative glucose disposal correlated in young (r = 0.69, P = 0.01) but not in the elderly (r = 0.064, P = 0.8 2) males, and this relationship was not influenced by the degree of ob esity. In conclusion, muscle fibre type and GS activity are both deter minants of muscle glycogen metabolism in healthy, normoglycaemic males . The close relationship between nonoxidative glucose metabolism and G S activity in young males is altered in ageing.