title: Physiological insulinemia acutely modulates plasma leptin.
abstract: Whether insulin acutely regulates plasma leptin in humans is controversial. We examined the dosage-response and time-course characteristics of the effect of insulin on leptin in 10 men (age 42+/-2 years [mean+/-SE]; BMI 29.3+/-2.0 kg/m2). Each individual underwent four 9-h euglycemic clamps (insulin at 20, 40, 80, and 400 mU x m[-2] x min[-1) and a control saline infusion. Although plasma glucose and insulin levels remained constant, leptin diminished from 9.1+/-3.0 to 5.9+/-2.1 ng/ml (P < 0.001) by the end of the control experiment. Conversely, plasma leptin showed a dosage-dependent increase during the insulin infusions that was evident within 30-60 min. The insulin-induced increase in leptin was proportionately lower in obese insulin-resistant men. Free fatty acids (FFAs) decreased during insulin and did not change during saline infusions. ED50 (the dose producing half-maximal effect) for insulin's effect on leptin and FFA was similar (138+/-36 vs. 102+/-24 pmol/l, respectively; P=0.11). To further define the role of physiological insulinemia, we compared the effect of a very low dosage insulin infusion (10 mU x m[-2] x min[-1]) with that of a control saline infusion in another group of 10 men (mean age 39+/-3 years; BMI 27.1+/-1.0 kg/m2). Plasma leptin remained stable during that insulin infusion, but fell by 37+/-2% in the control experiment. Thus physiological insulinemia can acutely regulate plasma leptin. Insulin could mediate the effect of caloric intake on leptin and could be a determinant of its plasma concentration. Inadequate insulin-induced leptin production in obese and insulin-resistant subjects may contribute to the development or worsening of obesity.
authors.affiliation: Department of Medicine, University of Southern California Medical School, Los Angeles 90024, USA. msaad@med1.medsch.ucla.edu
authors.forename: M F
authors.initials: MF
authors.lastname: Saad
authors.forename: A
authors.initials: A
authors.lastname: Khan
authors.forename: A
authors.initials: A
authors.lastname: Sharma
authors.forename: R
authors.initials: R
authors.lastname: Michael
authors.forename: M G
authors.initials: MG
authors.lastname: Riad-Gabriel
authors.forename: R
authors.initials: R
authors.lastname: Boyadjian
authors.forename: S D
authors.initials: SD
authors.lastname: Jinagouda
authors.forename: G M
authors.initials: GM
authors.lastname: Steil
authors.forename: V
authors.initials: V
authors.lastname: Kamdar
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006801:Humans; D007262:Infusions, Intravenous; D007328:Insulin / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology; D007333:Insulin Resistance; D020738:Leptin; D008297:Male; D009765:Obesity / Q000097:blood; D011506:Proteins / Q000378:metabolism*; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D020738:Leptin; D011506:Proteins