Regulation of plasma leptin in mice: influence of age, high-fat diet and fasting

1997.-Mechanisms regulating circulating leptin are incom-pletely understood. We developed a radioimmunoassay for mouse leptin to examine the influence of age, dietary fat content, and fasting on plasma concentrations of leptin in the background strain for the oblob mouse, the C57BL/6J mouse. Plasma leptin increased with age [5.3-+ 0.6 rig/ml at 2 mo (n = 23) vs. 14.2 t 1.6 rig/ml at ll & mo (n = 15), P < O.OOl]. Across all age groups (2-11 mo, n = 160), log plasma leptin correlated with body weight (r = 0.68, P < O.OOOl), plasma insulin (r = 0.38, P < O.OOl), and amount of intra-abdominal fat (r = 0.90, P < O.OOl), as revealed by magnetic resonance imaging. Plasma leptin was increased by a high-fat diet (58% fat for 10 mo) and reduced by fasting for 48 h. The reduction of plasma leptin was correlated with the reduction of plasma insulin (r = 0.43, P = 0.012) but not with the initial bod