Endocrine Abstracts

Introduction: Melatonin plays a key role in the circadian timing system. The question remains whether changes in endogenous melatonin may be associated with food intake. Orexin and ghrelin are involved in the regulation of energetic homeostasis. Therefore, we decided to obtain more detailed data on the circadian changes of orexin, ghrelin and melatonin for identification of the changes in these hormones to food intake and day-time, together with glycemic and C-peptide levels.

Methods: Five women (mean age 31.6±2.8 years, mean BMI 23.2±2.3 kg/m²) in follicular phase of menstrual cycle was examined. The levels of orexin, ghrelin, melatonin, C-peptide and glucose were studied during a daily regimen (16 h) including standardized food intake. The diurnal profiles of the hormones and serum glucose were evaluated using ANOVA with Period and Subject as independent factors. The correlations between melatonin and the remaining parameters were assessed by Pearson’s correlations and using a multiple stepwise backward regression model consisting of the time factor as a polynomial, and serum C-peptide and glucose. The study was approved by local Ethical Committe.

Results: The levels of blood glucose and C-peptide reflected periodic food intake being in a physiological range. A significant negative correlation between melatonin and C-peptide was found (Pearson’s correlation, r=−0.5525, P<0.0001, n=50, partial correlation r=−0.3532, P<0.02, n=50). A borderline significant relationship between melatonin and blood glucose was detected (Pearson’s correlation, r=−0.4679, P<0.0006, n=50). Ghrelin negatively correlated with C-peptide (r=−0.356, P<0.02). We found positive correlation between melatonin and ghrelin (r=0.453, P<0.003). Our results showed no significant correlation between orexin levels and other measured variables.

Conclusions: The negative relationship between melatonin and C-peptide as well as relatively rapid changes in melatonin levels permits speculation about food as one of the factors influencing daytime melatonin production.

The study was supported by grant: NR9055-4 IGA MZCR and GAUK.