The effect of acute lithium administration on brain monoamine synthesis and the precursor amino acids tyrosine and tryptophan in brain and plasma in rats.

The effect of a single i.p. injection of lithium chloride on brain monoamine synthesis and tyrosine and tryptophan levels in brain and plasma in rats was studied. Acute lithium administration was found to decrease brain tyrosine levels, which most likely was due to decreased plasma tyrosine levels. Brain tryptophan levels were mainly unaffected whereas plasma tryptophan leves were slightly decreased at 8 hours after lithium administration. Brain catecholamine synthesis was decreased at 4 hours and increased at 48 hours after the injection of lithium. Brain 5-hydroxytryptamine (5-HT) synthesis was decreased at all time intervals after the injection of lithium. It is concluded that the effects of acute lithium administration on brain monoamine synthesis are not mainly due to its effect on brain tyrosine and tryptophan levels in rats. Furthermore acute lithium administration appears to affect 5-HT synthesis to a greater extent than it affects catecholamine synthesis.