Neuropeptide Y and α-MSH Circadian Levels in Two Populations with Low Body Weight: Anorexia Nervosa and Constitutional Thinness

CONTEXT: Anorexia nervosa (AN) presents an adaptive appetite regulating profile including high levels of ghrelin and 26RFa (orexigenic) and low levels of leptin and PYY (anorexigenic). However, this adaptive mechanism is not effective in promoting food intake. The NPY/proopiomelanocortin (POMC) system plays a crucial role in the regulation of feeding behavior as NPY is the most potent orexigenic neuropeptide identified so far and as the POMC-derived peptide α-MSH drastically reduces food intake, and this peptidergic system has not been thoroughly studied in AN. OBJECTIVE: The aim of the present study was thus to investigate whether a dysfunction of the NPY/POMC occurs in two populations with low body weight, AN and constitutional thinness (CT). DESIGN AND SETTINGS: This was a cross-sectional study performed in an endocrinological unit and in an academic laboratory. INVESTIGATED SUBJECTS: Three groups of age-matched young women were studied: 23 with AN (AN), 22 CT and 14 normal weight controls. MAIN OUTCOME MEASURES: Twelve-point circadian profiles of plasma NPY and α-MSH levels were measured in the three groups of investigated subjects. RESULTS: No significant circadian variation of NPY was detected between the three groups. Plasma α-MSH levels were significantly lower in AN (vs controls) all over the day. The CT group, compared to controls, presented lower levels of α-MSH in the morning and the evening, and an important rise during lunchtime. CONCLUSION: In AN patients, the NPY system is not up-regulated under chronic undernutrition suggesting that this may play a role in the inability of anorectic women to adapt food intake to their energy demand. In contrast, low circadian α-MSH levels integrate the adaptive profile of appetite regulation of this disease. Finally, in CT women, the important α-MSH peak detected during lunchtime could explain why these patients are rapidly food satisfied.