The effect of melatonin administration on pituitary hormone secretion in man.
OBJECTIVE
Evidence is accumulating that the nocturnal increase in melatonin may influence pituitary hormone secretion. The aim of this study was to determine the effect of exogenous melatonin, in concencetrations spanning the physiological range, on the release of pituitary hormones in man during daylight hours.


METHODS
A double blind, randomized, crossover study.


METHODS
Eight healthy male volunteers with a mean age of 21 +/- 0.5 years were studied on four occasions, observations being made after the adminstration of melatonin in doses of 0.05, 0.5 or 5.0 mg or placebo. They refrained from taking heavy exercise, alcohol and from smoking for 24 h prior to the study.


METHODS
Serum cortisol, growth hormone, prolactin and plasma oxytocin, vasopressin, sodium, osmolality and packed cell volume were measured in samples taken at 30 minutes intervals for 150 minutes after the administration of melatonin.


RESULTS
Melatonin produced dose-dependent changes in circulating concentrations of oxytocin and vasopressin, the 0.5 mg dose being stimulatory, while 5.0 mg was inhibitory. These two doses stimulated growth hormone release, while there was no significant effect on prolactin or cortisol release.


CONCLUSIONS
These results confirm that the nocturnal increase in melatonin could contribute to the patterns of oxytocin, vasopressin and growth hormone release seen over 24 h.
Forsling
M L
ML
Departments of Gynaecology and Physiology King's College, St Thomas' Campus, London, UK. m.forsling@umds.ac.uk
Wheeler
M J
MJ
Williams
A J
AJ
D000328:Adult; D019540:Area Under Curve; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D013006:Growth Hormone / Q000097:blood; D006400:Hematocrit; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009994:Osmolar Concentration; D010121:Oxytocin / Q000097:blood; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D010907:Pituitary Hormones / Q000097:blood / Q000378:metabolism*; D011388:Prolactin / Q000097:blood; D012964:Sodium / Q000097:blood; D014667:Vasopressins / Q000097:blood
D010907:Pituitary Hormones; D014667:Vasopressins; D010121:Oxytocin; D011388:Prolactin; D013006:Growth Hormone; D012964:Sodium; D008550:Melatonin; D006854:Hydrocortisone