INSULIN REGULATION OF GLUCOSE AND LIPID-METABOLISM IN MASSIVE OBESITY

Eight obese patients and 12 normal individuals underwent a euglycaemic insulin clamp (20 and 40 mU · m2-1 · min-1) along with continuous infusion of 3-3H-glucose and 1-14C-palmitate and indirect calorimetry. Basal plasma glucose concentration (4.7±0.3 vs 4.4±0.2 mmol/l) was similar in the two groups, whereas hepatic glucose production was slightly higher in obese individuals (1.11±0.06 vs 0.84±0.05 mmol/min) in spite of higher plasma insulin levels (17±2 vs 6±1 mU/l; p<0.01). Insulin inhibition of hepatic glucose production was impaired in obese subjects. Glucose disposal by lean body mass was markedly reduced both at baseline (11.7±1.1 vs 15.6±0.6 μmol · kg-1 · min-1; p<0.05) and during clamp (15.0±1.1 vs 34.4±2.8 and 26.7±3.9 vs 62.2±2.8 μmol · kg-1 · min-1; p<0.01) Oxidative (12.2±1.1 vs 17.8±1 and 16.1±1.1 vs 51.1±1.7 μmol · kg-1 · min-1; p<0.05-0.002) and non-oxidative glucose metabolism (3.9±1.1 vs 15.0±2.8 and 12.8±3.3 vs 38.3±2.2 μmol · kg-1 · min-1; p<0.01-0.001) were impaired. Basal plasma concentrations of non-esterified fatty acids (635±75 vs 510±71 μmol/l) and blood glycerol (129±17 vs 56±5 μmol/l; p<0.01) were increased in obese patients. Following hyperinsulinaemia, plasma non-esterified fatty acids (244±79 vs 69±16 and 140±2 vs 36±10 μmol/l; p<0.01) and blood glycerol levels (79±20 vs 34±6 and 73±22 vs 29±5 μmol/l; p<0.01) remained higher in obese subjects. Baseline non-esterified fatty acid production rate per kg of fat body mass was significantly larger in normal weight subjects (37.7±6.7 vs 14.0±1.8 μmol/l; p<0.01) and insulin inhibition was reduced in obese patients (-41±9 vs -74±3 and -53±11 vs -82±3%; p<0.05). Basal plasma non-esterified fatty acid utilization by lean body mass was similar in the two groups (9.8±0.9 vs 8.8±2.0 μmol · kg-1 · min-1), whereas during clamp it remained higher in obese patients (6.0±1.2 vs 2.8±2.5 and 4.9±1.3 vs 1.5±0.6 μmol · kg-1 · min-1; p<0.1-0.05). Lipid oxidation was higher in obese individuals in spite of hyperinsulinaemia (3.7±0.3 vs 2.4±0.4 and 2.3±0.4 vs 0.9±0.3 μmol · kg-1 · min-1; p<0.05- 0.02). An inverse correlation was found between lipid oxidation and glucose oxidation (r=0.82 and 0.93; p<0.001) and glucose utilization (r=0.54 and 0.83; p<0.05-0.001) both in obese and control subjects. A correlation between lipid oxidation and non-oxidative glucose metabolism was present only in normal weight individuals (r=0.75; p<0.01). We conclude that in obesity all tissues (muscles, liver, and adipose tissue) are resistant to insulin action. Insulin resistance involves glucose as well as lipid metabolism. © 1990 Springer-Verlag.