Effects of diet and serotonergic agonist on hepatic apolipoprotein B-100 secretion and endothelial function in obese men

Abstract

We studied the effects of a hypocaloric diet with or without a serotonergic agonist (dexfenfluramine, Df) on the hepatic secretion of very-low-density-lipoprotein (VLDL) apoB and endothelial function of the forearm microcirculation in 20 viscerally obese men. The kinetics of VLDL apoB were studied using an infusion of 1-(13C)-leucine. Isotopic enrichment of apo B was measured using gas-chromatography mass spectrometry, and a multicompartmental model was used to estimate kinetic functions. Forearm vasodilatation was measured following an ischaemic stimulus using strain-gauge plethysmography, and visceral adipose tissue mass using magnetic resonance imaging. Compared with leaner subjects, the obese men had significantly higher hepatic apoB secretion (p < 0.05) and lower forearm flow debt repayment (p < 0.001). Both treatments produced similar decreases (p < 0.05) in body weight, waist circumference, visceral adipose tissue and fasting plasma insulin. With diet alone, there was a significant decrease (p < 0.05) in the plasma concentration and pool size hepatic secretion rate of VLDL apoB, as well as a significant increase (p < 0.05) in post-ischaemic flow debt repayment. With diet plus Df, there were parallel responses in these variables, but only decreased forearm vascular resistance (p < 0.05) was statistically significant. Combining both data sets, there was a highly significant reduction in hepatic apoB secretion rate (20.9 ± 2.0 vs. 14.7 ± 1.6 mg/kg fat-free mass/day, p = 0.005), as well as an increase in both maximal forearm blood flow (16.8 ± 7.5 vs. 22.2 ± 8.5 ml/100 ml/min, p = 0.006) and flow debt repayment (3.5 ± 2.1 vs. 5.4 ± 2.8 ml/100 ml, p 0.01), and a decrease in vascular resistance (6.7 ± 3.7 vs. 5.1 ± 4.4 mmHg/ml/100 ml/min, p = 0.007). Obese men have increased hepatic secretion of apoB and endothelial dysfunction of the forearm microcirculation, and decreasing their visceral adipose tissue mass by diet (with or without a serotonergic agonist) improves these abnormalities. This may provide a mechanistic basis for the reduction in cardiovascular risk in obese patients who lose weight.