ABSTRACT
The plasma concentration of leptin is reduced in association with chronic energy restriction and weight loss in humans, but little is known about the acute effects of fasting and glucose infusion on leptin. In this study, plasma leptin, insulin, glucose, and fatty acid concentrations were measured daily in 14 healthy, normal-weight, female volunteers aged 24 +/- 4 y with a body mass index (kg/m2) of 24.2 +/- 3.6 during a 4-d fast. The mean plasma leptin concentration decreased by 54 +/- 8% with fasting (P = 0.0006, ANOVA). In a stepwise-regression model, the change in leptin concentration with fasting correlated most significantly with the change in insulin (R2 = 0.48, P = 0.0057) and to a lesser extent with the change in body fat by bioimpedance analysis (R2 = 0.19, P = 0.03). Plasma leptin concentrations measured every 20 min from 2000 to 0800 on the fourth night of the fast did not show a time-dependent rise. A continuous intravenous infusion of 5% glucose providing 1414 +/- 323 kJ/d (338 +/- 78 kcal/d) was begun after 4 d of fasting in seven subjects who continued to fast for an additional 6 d. Within 24 h of the glucose infusion, leptin concentrations increased significantly by 80 +/- 52% (P < 0.05). These data show the sensitivity of plasma leptin concentrations to small changes in energy supply and suggest a basic role of substrate metabolism in the short-term regulation of leptin.
Subject(s)
Fasting/metabolism , Glucose/pharmacology , Proteins/drug effects , Adult , Blood Glucose , Fatty Acids/blood , Female , Glucose/administration & dosage , Humans , Infusions, Intravenous , Insulin-Like Growth Factor I/metabolism , Leptin , Proteins/metabolism , Radioimmunoassay , Regression AnalysisABSTRACT
The weight-average molecular weight of the Mo-Fe protein isolated from Azotobacter vinelandii has been determined by sedimentation-equilibrium techniques. In buffer, the value is 245000+/-5000; in 8M-urea, the value is 61000+/-1000. The protein was separated into two components by chromatography on CM-cellulose in 7M-urea, pH 4.5. These components have similar molecular weights but were shown to differ in charge, amino acid content and arginine-containing peptides. It is proposed that the tetramer has the subunit composition (nalpha2nbeta2).
