No abstract

The contribution of gluconeogenesis (GNG) to endogenous glucose output (EGO) in type 2 diabetes is controversial. Little information is available on the separate influence of obesity on GNG. We measured percent GNG (by the 2 H 2 O technique) and EGO (by 6,6-[ 2 H]glucose) in 37 type 2 diabetic subjects (9 lean and 28 obese, mean fasting plasma glucose [FPG] 8.3 ± 0.3 mmol/l) and 18 control subjects (6 lean and 12 obese) after a 15-h fast. Percent GNG averaged 47 ± 5% in lean control subjects and was significantly increased in association with both obesity (P < 0.01) and diabetes (P = 0.004). By multivariate analysis, percent GNG was independently associated with BMI (partial r = 0.27, P < 0.05, with a predicted increase of 0.9% per BMI unit) and FPG (partial r = 0.44, P = 0.0009, with a predicted increase of 2.7% per mmol/l of FPG). In contrast, EGO was increased in both lean and obese diabetic subjects (15.6 ± 0.5 µmol · min -1 · kg -1 of fat-free mass, n = 37, P = 0.002) but not in obese nondiabetic control subjects (13.1 ± 0.7, NS) as compared with lean control subjects (12.4 ± 1.4). Consequently, gluconeogenic flux (percent GNG ؋ EGO) was increased in obesity (P = 0.01) and markedly elevated in diabetic subjects (P = 0.0004), whereas glycogenolytic flux was reduced only in association with obesity (P = 0.05). Fasting plasma glucagon levels were significantly increased in diabetic subjects (P < 0.05) and positively related to EGO, whereas plasma insulin was higher in obese control subjects than lean control subjects (P = 0.05) and unrelated to measured glucose fluxes. We conclude that the percent contribution of GNG to glucose release after a 15-h fast is independently and quantitatively related to the degree of overweight and the severity of fasting hyperglycemia. In obese individuals, reduced glycogenolysis ensures a normal rate of glucose output. In diabetic individuals, hyperglucagonemia contributes to inappropriately elevated rates of glucose output from both GNG and glycogenolysis. Diabetes 49:1367-1373, 2000 P atients with type 2 diabetes typically show an increase in endogenous glucose output (EGO) (1-3). Several observations indicate that gluconeogenesis (GNG) is increased in type 2 diabetes. First, there is an increased protein turnover and hence release of gluconeogenic amino acids. Second, in obese patients with type 2 diabetes, the increased fat mass and rate of lipolysis contribute substrate (glycerol) (4,5) and activation (free fatty acids) (6,7) for GNG. Third, the net uptake of all gluconeogenic precursor substrates by the liver is increased. Using splanchnic catheterization, Felig et al. (8) estimated that in diabetic subjects, conversion into glucose of gluconeogenic precursors could represent 30% of splanchnic glucose output versus 20% in lean nondiabetic subjects (8). Although net splanchnic substrate uptake cannot account for the whole of GNG, this finding is nevertheless compatible with enhanced GNG in diabetes. Finally, tracer studies have shown that in obese type 2 diabetic patients...

Visceral fat (VF) excess has been associated with decreased peripheral insulin sensitivity and has been suggested to contribute to hepatic insulin resistance. However, the mechanisms by which VF impacts on hepatic glucose metabolism and the quantitative role of VF in glycemic control have not been investigated. In the present study 63 type 2 diabetic subjects (age, 55 +/- 1 yr; fasting plasma glucose, 5.5-14.4 mmol/liter; hemoglobin A(1c), 6.1-11.7%) underwent measurement of 1) fat-free mass ((3)H(2)O technique), 2) sc and visceral abdominal fat area (magnetic resonance imaging), 3) insulin sensitivity (euglycemic insulin clamp), 4) endogenous glucose output ([(3)H]glucose infusion technique), and 5) gluconeogenesis ((2)H(2)O method). After adjustment for sex, age, body mass index, diabetes duration, ethnicity, and sc fat area, VF area was positively related to fasting hyperglycemia (partial r = 0.46; P = 0.001) as well as to hemoglobin A(1c) (partial r = 0.50; P = 0.0003). Insulin sensitivity was reciprocally related to VF independently of body mass index (partial r = 0.33; P = 0.01). In contrast, the relation of basal endogenous glucose output to VF was not statistically significant. This lack of association was explained by the fact that VF was positively associated with gluconeogenesis flux (confounder-adjusted, partial r = 0.45; P = 0.003), but was reciprocally associated with glycogenolysis (partial r = 0.31; P < 0.05). We conclude that in patients with established type 2 diabetes, VF accumulation has a significant negative impact on glycemic control through a decrease in peripheral insulin sensitivity and an enhancement of gluconeogenesis.