Human skeletal muscle releases leptin in vivo.

Leptin is considered an adipokine, however, cultured myocytes have also been found to release leptin. Therefore, as proof-of-concept we investigated if human skeletal muscle synthesized leptin by measuring leptin in skeletal muscle biopsies. Following this, we quantified human skeletal muscle and adipose tissue leptin release in vivo.

The role of leptin in human lipid and glucose metabolism: the effects of acute recombinant human leptin infusion in young healthy males.

Background: Obese and lean humans treated with leptin have not experienced convincing weight-loss results compared with the dramatic weight losses observed in obese rodents.

Objective: We sought to investigate the effect of acutely elevating leptin to concentrations observed in obese individuals on muscle and adipose tissue metabolism and muscle signaling in healthy lean males.

Design: Healthy, lean, postabsorptive males were infused with either recombinant human leptin (rhleptin; n = 8) or saline (control; n = 8) for 4 h, which elicited leptin concentrations of ~ 20 and ~ 1 ng/mL, respectively.

IL-6 selectively stimulates fat metabolism in human skeletal muscle.

Interleukin (IL)-6 is chronically elevated in type 2 diabetes but also during exercise. However, the exact metabolic role, and hence the physiological significance, has not been elucidated. The objective of this study was to investigate the in vivo effect of recombinant human (rh) IL-6 on human fat and glucose metabolism and signaling of both adipose tissue and skeletal muscle.