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NOCTURNAL URINARY MELATONIN EXCRETION AND PLASMA CORTISOL LEVELS IN CHILDREN AND ADOLESCENTS AFTER A SINGLE ORAL DOSE OF DEXAMETHASONE

In the present study, the possible relationship between melatonin secretion as reflected by nocturnal melatonin excretion (2000 h‐0800 h) and the pituitary‐adrenocortical axis was investigated. Nocturnal urinary melatonin excretion and plasma cortisol levels were determined in 41 children with weight problems before and after a single oral dose of dexamethasone. A first group of 15 individuals with normal cortisol cycle (12·2 ± 1·4 at 0800 h and 3·1 ± 0·5 μg/100 ml at 1700 h), and levels below 1·0 μg/100 ml after dexamethasone, showed a highly significant increase in melatonin excretion during the night following dexamethasone treatment (63·5 ± 5·5 ng/12 h vs 33·6 ± 3·0 for the control night, P > 0·001). This increase was observed from prepuberty to young adulthood (pubertal stages PI—PV). In a second group of 16 subjects with mean cortisol levels similar at 0800 h and 1700 h (10·7 ± 1·3 and 9·3 ± 1·5 μg/100 ml respectively), but with a normal cortisol suppression after dexamethasone administration, nocturnal melatonin excretion increased from 21·2 ± 2·1 to 33·4 ± 3·0 ng/12 h (P > 0·01). A significant increase was found in prepubertal children (PI) whereas no change was observed at the end of pubertal development (stages PIV‐PV). A third group of 10 patients with both low amplitude cortisol cycles (16·2 ± 2·5 and 10·8 ± 2·4 μg/100 ml) and abnormal cortisol suppression after dexamethasone administration (9·1 ± 2·4 μg/100 ml), showed no increase in melatonin excretion (24·2 ± 2·7 and 24·9 ± 3·7 ng/12 h). However, one patient with delayed puberty had increased melatonin excretion after dexamethasone. No relationship was found between body weight and melatonin excretion. Six subjects with delayed puberty had high melatonin excretion before dexamethasone and showed a marked increase after dexamethasone treatment (76·1 ± 7·2 ng/12 h vs 38·6 ± 6·9 for the control night, P > 0·001), whatever the cortisol cycles and levels of suppression. Our results suggest a relationship between the patterns of cortisol and melatonin secretion. However, further studies are necessary to prove whether there exist interactions between the pituitary‐adrenal axis and the pineal gland and whether the response of melatonin to dexamethasone is also related to the stage of sexual maturation.