Decreased insulin sensitivity and muscle enzyme activity in elderly subjects.

Skeletal muscle glycogen deposition, and the activation of muscle glycogen synthase and pyruvate dehydrogenase during a hyerinsulinaemic euglycaemic clamp have been measured in six young and six elderly males matched for body mass index, physical activity and diet. Clamp glucose requirement (insulin, 0.1 U kg-1 h-1) was significantly lower in the older subjects (8.0 +/- 0.4 mg kg-1 min-1) than in younger subjects (10.5 +/- 0.6 mg kg-1 min-1, P less than 0.02). Although the older subjects had a 6.5% decrease in lean body mass, clamp glucose requirement expressed per unit of lean body mass was also significantly decreased in the older subjects (10.2 +/- 0.5 vs. 12.4 +/- 0.6 mg kg-1 min-1, P less than 0.05). The increase in muscle glycogen with the clamp was decreased by 33% in the older subjects (elderly: 13.1 +/- 1.3 mg g-1 protein, young: 19.6 +/- 2.2 mg g-1 protein; P less than 0.05), and was strongly correlated with clamp glucose requirement (r = 0.72, P less than 0.01). Glucose-6-phosphate independent glycogen synthase activity increased significantly between fasting and the end of the clamps in both groups (P less than 0.001), but was lower at the end of the clamp in the older subjects (P less than 0.05). Glycogen synthase activity at the end of the clamp correlated with both clamp glucose requirement (r = 0.83, P less than 0.01) and muscle glycogen deposition (r = 0.73, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)