Glucose-induced thermogenesis, inhibition of lipid oxidation rate and autonomic dysfunction in non-diabetic obese women.

Abstract

The aim of this study was to look for a relationship between autonomic dysfunction and alterations in glucose- induced thermogenesis (GIT) and lipid oxidation rate in obese non-diabetic women. 37 obese women, 20 with impaired cardiac autonomic function tests (group 1) were matched with 17 women with normal tests (group 2) according to age, weight, body mass index (BMI), waist-to-hip ratio (WHR), fat mass (FM) and fat free mass (FFM). A series of five standardized tests was carried out, three of which were based mainly on cardiac parasympathetic control (heart rate response to Valsalva, deep breathing and lying-to-standing) and two on cardiovascular sympathetic function (blood pressure response to standing and to handgrip). Energy expenditure (EE), lipid and glucose oxidation rate were determined by indirect calorimetry at fasting and after an oral glucose load (75 g). Blood glucose, insulin and catecholamines responses to glucose were examined. There was no significant difference in plasma glucose, insulin, catecholamines, metabolic rate, glucose and lipid oxidation rate at fasting and plasma glucose, insulin and catecholamine responses to glucose. GIT was slightly but not significantly lower in group 1 (24.7+/-10.4 kJ) than in group 2 (46.8+/-9.0 kJ). The cumulative glucose oxidation rate did not differ significantly in the two groups. The cumulative lipid oxidation rate was significantly lower in group 1 than in group 2 (-49.4+/-4.1 vs -30.8+/-8.0, respectively, P = 0.033). It correlated negatively with the area under the curve of insulin response (r=-0.37, P=0.04). In the multivariate analysis, both autonomic dysfunction and the area under the curve of insulin response correlated significantly with the cumulative lipid oxidation rate. This study suggests that 1) the glucose-induced inhibition of the lipid oxidation rate in obese women is greater in the patients with autonomic dysfunction; 2) a decrease in sympathetic activity is likely to be involved in this phenomenon.