ACUTE INSULIN ADMINISTRATION DOES NOT AFFECT PLASMA LEPTIN LEVELS IN LEAN OR OBESE SUBJECTS

Whether leptin levels are related to insulin sensitivity or subject to acute regulation by insulin is not known. In 12 obese [body mass inde x (BMI) = 34.0 +/- 1.5 kg m(-2)] and 12 lean (BMI = 22.2 +/- 0.6 kg m( -2)) non-diabetic subjects, plasma leptin concentrations were measured in the fasting state and during 2 hours of euglycaemic hyperinsulinae mia (similar to 600 pmol L(-1)). Fasting plasma leptin was significant ly higher in obese (26.6 +/- 3.2) than in lean subjects (6.4 +/- 1.2 n g mL(-1), P = 0.0001), and in women (21.1 +/- 3.3) than in men (7.3 +/ - 2.3 ng mL(-1), P = 0.01). In univariate analysis, fasting plasma lep tin was strongly related to all anthropometric measures (body weight, fat mass, percent fat mass, waist and hip circumferences). In multiple regression, per cent adiposity, hip circumference and duration of obe sity explained 90% of the variability in fasting leptin concentrations . Fasting and stimulated (OGTT) insulin levels, insulin sensitivity (2 2.6 +/- 1.9 vs 36.7 +/- 2.0 mu mol min(-1) kg(-1) in lean and obese su bjects, respectively, P < 0.0001), glucose area, and serum triglycerid es were positively related to fasting plasma leptin concentrations; no ne of these associations, however, was statistically significant after adjusting for BMI. During the clamp, plasma leptin concentrations rem ained constant in both lean and obese subjects. We conclude that neith er insulin levels nor sensitivity relate to leptin levels independentl y of fat mass, and that leptin is not subject to acute (2 hours) regul ation by insulin in lean or obese humans.