Pineal melatonin secretion exhibits a rhythm which is identified as a
circadian cycle with a period of between 20 and 28 h in most animals.
The melatonin rhythm has an acrophase of about -30 degrees. The aim of
this study was determine the effect of lithium on the melatonin rhyth
m since lithium is usually used as a therapeutic agent in manic-depres
sive desease. Lithium induced a delay of the melatonin acrophase which
reached a value of about -45 degrees; lithium also produced another p
eak which had an acrophase at about +60 degrees. We speculate that lit
hium influences either inositol phosphate turnover or it merely change
s the profile of the melatonin rhythm.