Aim: In human obesity, there is some evidence for impaired adrenergic sensitivity with respect to catecholamine-induced lipolysis. The β-adrenoceptor agonist isoprenaline has been shown to suppress plasma leptin levels in lean humans in vivo. We hypothesized that a reduced adrenergic sensitivity in obese humans would result in impaired suppression of leptin secretion.
Methods: Eight obese [Ob, body mass index (BMI) = 33.3 kg/m2] and seven lean (Ln, BMI = 21.8 kg/m2) men were studied after an overnight fast. Intravenous isoprenaline infusion was initiated at a rate of 8 ng/kg/min, titrated up to 24 ng/kg/min over 30 min and continued at this rate for a further 120 min with continuous electrocardiogram monitoring.
Results: Baseline fasting plasma leptin was higher in obese compared with lean subjects (Ob 12.2 ± 1.8, Ln 2.6 ± 0.6 ng/ml, p < 0.05 unpaired t-test). Baseline fasting glycerol as a measure of lipolysis was similar in both groups (Ob 62.9 ± 7.6, Ln 42.4 ± 8.9 µmol/l) and increased from baseline to 150 min by equivalent amounts (Ob +66.9%, Ln +81.2%, p = NS). Plasma leptin decreased from baseline to 150 min with similar relative changes in both groups (Ob −29.2%, Ln −27.8%).
Conclusions: Obese subjects show a similar lipolytic and leptin response to acute isoprenaline infusion compared with lean subjects. Impaired β-adrenergic-induced inhibition of leptin secretion does not appear to contribute to hyperleptinaemia in obese human subjects.