Abstract 164

Purpose: In adults, leptin seems to cross blood-brain barrier (BBB) by a saturable transporter. This may contribute to the development of obesity. The present study in healthy children investigates leptin levels in plasma and CSF in relation to body mass index (BMI).

Methods: Prospective study (1995 - 98), tertiary care facility, approval of the local Ethical committee. Analysis of leptin levels (RIA, Mediagnost, Tübingen, Germany) in stored plasma and CSF samples (-80 °C) of patients without CNS-infection. Inclusion criteria: 1) temp. <38.5 °C, 2) CRP <10 mg/l, 3) CSF-leukocytes < 107/1, 4) no need for neurosurgical or oncological treatment, 5) no history of trauma. Four groups according to BMI.

Results: 65 children (28 girls, 37 boys). Plasma leptin [ng/ml] was (median; interquartile ranges) 7.4 (2.3-12.6) in girls and 2.6 (1.3-5.5) in boys, CSF leptin [ng/ml] was 0.273 (0.134-0.387) and 0.204 (0.113 - 0.327), resp., leading to CSF/plasma ratios [%] of 4.5 (2.0 - 8.0) and 7.1 (3.9 - 11.5), resp. Ratios were clearly dependent from BMI percentiles (r = -0.484, p < 0.01): median leptin plasma levels in the four groups (BMI < 10th, 10th-50th, 50th-90th, and 90th percentile) were 2.0 (1.0 - 4.2), 2.3 (1.4 - 3.1), 4.1 (1.2 - 12.2) and 8.8 (6.6 - 13.2) ng/ml, CSF/plasma ratios were inversely related: 8.2 (5.4 - 12.4), 7.6 (5.0 - 15.0), 5.5 (2.8 - 7.2) and 3.6 (1.7 - 5.5) % (ANOVA: significant differences between groups).

Discussion: Also in children, CSF leptin seems to "underrepresent" true fat mass in obese subjects, possibly due to nonlinear transport across BBB. This mechanism may either lead to obesity, but may also protect lean subjects against inadequate loss of fat mass.