ObjectiveThe objective of the present study was to examine the impact of major heart surgery with cardiopulmonary bypass (CPB) in childhood on serum leptin concentrations in relation to plasma cortisol, epinephrine, norepinephrine, and insulin.DesignControlled, prospective study.SettingIntensive care unit of a university hospital.Patients and InterventionsWe enrolled 20 pediatric patients undergoing open heart surgery and 20 children with major surgery not necessitating CPB (surgical control group). Leptin was measured by radioimmunoassay, cortisol and insulin were measured by chemiluminescence, and epinephrine and norepinephrine were measured by high-pressure liquid chromatography.Measurements and Main ResultsIn the CPB group, leptin dropped from 0.4 ± 0.1 preoperatively (mean ± sem) to 0.2 ± 0.1 ng/mL intraoperatively (p< .05). It increased to 1.6 ± 0.7 ng/mL 12 hrs after surgery (p< .01) and declined thereafter. In the surgical controls, leptin rose from 0.5 ± 0.2 ng/mL before surgery to 1.8 ± 0.8 ng/mL 12 hrs after surgery (p= .001). In both groups, plasma cortisol, insulin, and epinephrine significantly increased after surgery. There was no relationship between the maximum increase of serum leptin and the other hormones.ConclusionsPatients with CPB surgery and non-CPB surgery show a similar increase in serum leptin, indicating that sepsislike inflammatory syndrome does not further increase elevated leptin concentrations following major surgery. In this complex situation, serum leptin does not appear to be merely regulated by its known stimuli and suppressors.