Insulin binding and action in adipocytes in vitro in relation to insulin action in vivo in young and middle-aged subjects.

Abstract

The effect of age on glucose metabolism in vivo was compared to that found in adipocytes in vitro in young (n = 8, age 23 to 31 years) and middle-aged (n = 7, age 37 to 55 years) non-diabetic subjects. During the OGTT, the incremental glucose or insulin areas did not differ significantly between the groups. Fasting and 2 h plasma glucose (P less than 0.01) and the 2 h plasma insulin (P less than 0.05) levels were, however, slightly higher in the middle-aged than in the young group. During iv induced hyperinsulinaemia (approximately 85 mU/l), rates of glucose uptake were comparable between the middle-aged (6.32 +/- 0.94 mg/kg/min) and the young subjects (7.56 +/- 0.78 mg/kg/min, P greater than 0.5). In fat cells, both basal and insulin stimulated rates of glucose transport were 35% lower (P less than 0.05) in the middle-aged than in the young subjects. Basal and insulin stimulated rates of glucose oxidation and lipogenesis were both markedly lower (P less than 0.01) in the middle-aged than in the young group. The rates of glucose transport, oxidation and lipogenesis were inversely related to age, whereas none of these parameters was related to fat cell size. In conclusion, adipocyte glucose metabolism in middle-aged healthy subjects was markedly impaired. In contrast, rates of glucose uptake during iv hyperinsulinaemia and glucose responses during hyperinsulinaemia in the OGTT were comparable in young and middle-aged subjects.(ABSTRACT TRUNCATED AT 250 WORDS)