Characterization of nocturnal ultradian rhythms of melatonin in children with growth hormone-dependent and independent growth delay

To assess the existence of a possible nocturnal ultradian rhythm of melaton in in children, we analyzed 28 pediatric patients (mean age, 9.08 +/- 2.2 y r) with GH-dependent and GH-independent growth delay. Plasma melatonin was measured by RIA in children sampled every 30 min between 2100-0900 h. Stati stical analysis consisted of cluster analysis to examine the presence of pe aks and troughs. The pattern of melatonin levels was related to the cause o f growth delay, although the means of the nocturnal concentrations of melat onin were similar in all children. Interestingly, children with a GH defici t showed st nearly normal melatonin profile, whereas children with normal G K values but abnormal growth displayed atypical profiles of melatonin. The results also prove the existence of an ultradian rhythm of melatonin in mos t of the patients studied. The ultradian rhythm of melatonin in children wa s characterized by irregular interburst intervals, thus differing from the rhythm previously described in adults that had an almost constant pulse fre quency. Moreover, the existence of low and high melatonin producers was rev ealed in the study, a feature unrelated to the cause of growth delay. The g roup of children with a GH deficit showed the lowest values of integrated m elatonin production and of the area of peaks and troughs. These results pro ve that children exhibit an ultradian rhythm of melatonin like that in adul ts. Whereas it is riot clear whether the episodic production of melatonin i s required for its biological actions, the existence of irregular pulses ma y reflect endocrine influences at this age and/or the immaturity of the int rinsic pulse generator.