Melatonin administration and pituitary hormone secretion.
OBJECTIVE
The relationship between the pineal gland and pituitary function remains controversial, while the role of melatonin in the adaptation of the organism to the light-dark cycle of the environment is becoming increasingly recognized. The aim of this study was to investigate the effect of a manipulation of the melatonin rhythm on pituitary hormone secretion in man.


METHODS
Double-blind controlled clinical study.


METHODS
Ten adult healthy male volunteers, aged 21-33 years, were studied on two occasions: once after the administration of melatonin 5 mg orally for 4 days at 1700 hours and once after the administration of placebo, at similar times. On the day of each study the subjects undertook their normal duties but refrained from taking heavy exercise, from smoking and drinking alcohol.


METHODS
Serum cortisol, growth hormone, prolactin and plasma vasopressin, oxytocin, melatonin, sodium, potassium, osmolality and packed cell volume were measured over the following 24 hours.


RESULTS
The cortisol peak was advanced and prolactin release increased after melatonin administration, while growth hormone was not affected. Vasopressin and oxytocin levels were found to increase during the night in the control study, but the period of the nocturnal increase in vasopressin concentrations was reduced after the administration of melatonin and the nocturnal increase of oxytocin was absent.


CONCLUSIONS
Altering the melatonin rhythm may affect neuroendocrine function, influencing the nocturnal pattern of neurohypophysial hormone secretion, augmenting prolactin release and advancing the peak of cortisol release.
Kostoglou-Athanassiou
I
I
Department of Gynaecology, St. Thomas' Hospital, UMDS, London, UK.
Treacher
D F
DF
Wheeler
M J
MJ
Forsling
M L
ML
D000284:Administration, Oral; D000328:Adult; D000704:Analysis of Variance; D002940:Circadian Rhythm; D018592:Cross-Over Studies; D004311:Double-Blind Method; D013006:Growth Hormone / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D008550:Melatonin / Q000097:blood / Q000494:pharmacology*; D010121:Oxytocin / Q000097:blood / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000187:drug effects* / Q000378:metabolism; D010907:Pituitary Hormones / Q000097:blood / Q000378:metabolism*; D011388:Prolactin / Q000097:blood; D014667:Vasopressins / Q000097:blood / Q000378:metabolism
D010907:Pituitary Hormones; D014667:Vasopressins; D010121:Oxytocin; D011388:Prolactin; D013006:Growth Hormone; D008550:Melatonin; D006854:Hydrocortisone