Circadian fluctuation of plasma melatonin in Prader-Willi's syndrome and obesity

In 3 groups of 8 children and adolescents each with Prader-Willi-Labhart's Syndrome (PW-S), obese patients matched for body weight (control I), and normal weight subjects matched for pubertal stage (control II) plasma concentrations of melatonin, cortisol, growth hormone (hGH), insulin, gonadal hormones, and gonadotropins were measured every 1 to 4 hours in 24-hour-profiles. All hormones were determined by radioimmunoassay. The specific melatonin antibody was raised in rabbits. Criteria of the melatonin assay were as follows: detection limit for plasma concentrations of 13 pg/ml, intraassay and interassay variations: 8.4 and 11.2%, respectively. PW-S-patients showed cortisol fluctuations within normal limits. hGH was lower than 5 micrograms/l even during sleep, insulin ranged between 5 and 170 mU/l, and no excessively high glucose levels were found. Estradiol and testosterone were low for age and for pubertal development in all patients except in two girls. Basal LH and FSH levels were in the low normal range and showed sluggish response to LHRH. Plasma melatonin was low during the day, increased at mid-night and peaked at 3 a.m. Melatonin levels in PW-S were not significantly different from those in both control groups. We concluded that the impairment of gonadotropin secretion in patients with PW-S is not due to elevated levels of plasma melatonin.