The sympathetic nervous system may play a central role in the regulation of both lipolysis and leptin production. Therefore, we investigated the effect of intravenous infusions of the β-adrenergic agonist isoprenaline on plasma concentrations of leptin and nonesterified fatty acids.DESIGN AND PATIENTS
Eight lean, healthy human volunteers, (4M:4F; median (interquartile range) age 36.5 (30.8-40.0) years; BMI 22.9 (20.1-29.2)kg.m−2; % body fat 24.5 (17.9-26.3)), were studied following an overnight fast. Intravenous infusion of isoprenaline was carried out for 3 h, followed by a 1 hour recovery phase. The isoprenaline infusion rates (0.5-3.5 μg.min−1) were titrated individually for each subject in order to achieve similar biological sympathetic responses based on heart rate (target heart rates were > 100 min−1 but < twice resting heart rate).MEASUREMENTS
Plasma leptin was determined using an in-house radioimmunoassay, nonesterified fatty acids estimated with an enzymatic colourimetric assay and insulin concentrations were assayed using a specific, two-site immunoenzymometric assay.RESULTS
Fasting preinfusion plasma leptin concentrations (6.3 (3.0-12.8)μg/l) correlated with percentage body fat measured by bioimpedance (r = 0.95; P < 0.001). Plasma leptin concentrations were rapidly suppressed by isoprenaline, with maximal suppression (20.5 (15.0-25.0)% of preinfusion levels (Wilcoxon rank sum test; P < 0.05)), observed after 2 h. In the recovery period, plasma leptin concentrations rapidly returned to preinfusion levels (postinfusion vs maximally suppressed leptin concentrations P < 0.05; vs preinfusion leptin concentrations P = NS). Plasma nonesterified fatty acids and insulin concentrations showed opposite changes to those observed with leptin.CONCLUSION
Plasma leptin concentrations are rapidly and reversibly suppressed by the infusion of isoprenaline in humans in vivo.