Dopaminergic system mediation of stimulatory effect of melatonin on secretion of prolactin.
OBJECTIVE
The purpose of the present study was to clarify the mechanism of the stimulatory effect of melatonin on the secretion of prolactin.


METHODS
Determination was made of the levels of dopamine (DA), 3,4-dihydroxyphenlacetic acid (DOPAC), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in the median eminence of rats following intravenous melatonin (100 micrograms) administration.


RESULTS
Administration of 100 micrograms of melatonin to rats resulted in a significant increase in prolactin secretion (p < 0.01, analysis of variance). Administration of melatonin also resulted in significant decreases in the DOPAC content (p < 0.05) and in the DOPAC/DA ratio (p , 0.05) in the median eminence 1 hour after melatonin administration, at which time serum prolactin was maximal. However, no significant changes were detected in the content of 5-HT or 5-HIAA or in the 5-HIAA/5-HT ratio in the median eminence.


CONCLUSIONS
These results suggest that the stimulatory effect of melatonin on the secretion of prolactin might be mediated by dopaminergic mechanisms.
Okada
M
M
Department of Obstetrics and Gynecology, Kochi Medical School, Japan.
D000818:Animals; D004298:Dopamine / Q000378:metabolism*; D005260:Female; D008473:Median Eminence / Q000378:metabolism*; D008550:Melatonin / Q000502:physiology*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*
D012701:Serotonin; D011388:Prolactin; D008550:Melatonin; D004298:Dopamine