A LIQUID MIXED MEAL OR EXOGENOUS GLUCAGON-LIKE PEPTIDE-1 (GLP-1) DO NOT ALTER PLASMA LEPTIN CONCENTRATIONS IN HEALTHY-VOLUNTEERS

Glucagon-like peptide I [7 - 36 amide] (GLP-1) and the obese gene prod uct (leptin) are thought to be involved in the central regulation of f eeding. Both may act from the peripheral circulation to influence brai n function. To study potential interactions, GLP-1 ([7 - 36 amide]: 0. 4, 0.8 pmol kg(-1) min(-1) or placebo on separate occasions) was infus ed intravenously (from -30 to 240 min) into nine healthy volunteers [a ge 26 +/- 3 years, body mass index: 22.9 +/- 1.6kg/m(2), glycated haem oglobin HbA(1c): 5.0% +/- 0.2% (normal: 4.0% - 6.2%), creatinine: 1.1 +/- 0.1 mg/dl], and (at 0 min) a liquid test meal (50 g sucrose in 400 mi 8% amino acid, total amino acids 80 g/l) was administered via a na sogastric tube. Plasma leptin (radioimmunoassay, RIA), glucose, insuli n (microparticle enzyme immunoassay), C-peptide (enzyme-linked immunos orbent assay) and GLP-1 (RIA) were measured, and statistical analysis was done with repeated-measures ANOVA and Student's t-test. Plasma lep tin concentrations were 31 +/- 6 pmol/l in the basal state. They did n ot change within 240 min after meal ingestion nor in response to the i nfusion of exogenous GLP-1 [7 - 36 amide] (P = 0.99 for the interactio n of experiment and time) leading to GLP-1 mean plasma levels of 25 +/ - 2 and 36 +/- 3(basal 6 +/- 1) pmol/l. On the other hand, glucose (fr om basal 4.7 +/- 0.1 to 6.0 +/- 0.2 mmol/l at 15 min, P < 0.05) and in sulin (from basal 28 +/- 2 to 325 +/- 78 pmol/l at 45 min, P < 0.05) i ncreased clearly after the meal with pla cebo. In conclusion, (1)plasm a leptin levels in normal human subjects show no short-term changes af ter feeding a liquid mixed meal and (2) do not appear to be directly i nfluenced by physiological and pharmacological elevations in plasma GL P-1 [7 - 36 amide] concentrations. This does not exclude interactions at the cerebral (hypothalamic) level or on more long-term temporal sca les.