Circadian pattern of serum leptin and β-endorphin levels in obese and non obese women

To investigate diurnal profile of leptin and P-endorphin circulating levels and to assess any possible influence between these two peptides, 24-h serum concentrations of leptin and P-endorphin were examined in 24 obese (BMI 32. +/- 1 1.3) women and in 12 controls (BMI 21 +/- 0.5). Blood samples for leptin and P-endorphin determinations were drawn every four hours for 24 hours beginning at 8.00 am. Data were analyzed by unpaired t-test, linear regression and by inferential statistical procedures. We found a significant circadian rhythm for both peptides, either in obese or in controls. The 24-h mean leptin levels were significantly (p < 0.0001) higher (32.1 +/- 2.8 ng/ml; mean +/- SE) in obese women than controls (13.6 +/- 1. 1), with a peak time located after midnight in obese and controls. The 24-h P-endorphin mean levels were significantly (p < 0.0001) higher in obese than controls (30.6 +/- 2 vs 22 +/- 1.9pg/ml), with acrophase located in the early morning hours in both groups. Finally, we found a positive relationship (R-2= 0.303; p = 0.0005) between leptin and P-endorphin circadian mean levels. These results show that the time course of 24-h rhythm of leptin and P-endorphin are similar in obese and lean women. The positive relationship between 24-h leptin and P-endorphin mean levels allow us to speculate that leptin may be a likely candidate to increase P-endorphin levels in obese subjects.