Lithium Treatment Effect on Serotonin Function

To the Editor.—  The recent report by Price et al¹ in the January 1989 issue of the Archives examined the effect of short- and longterm lithium administration on serotonin function in depressed patients, using as an index the prolactin response to infusion of tryptophan. In contrast to our find ings in normal volunteers,² Price et al found an enhancement of prolactin responses after short-term lithium treatment only and not after long-term lithium treatment. There are a number of reasons that may account for the discrepancy between these studies.As the authors themselves point out, interpretation of their data is confounded by the pretreatment prolactin responses that were greater in the long-term lithium treatment group. A possible reason for this is the difference in the mean ages of the two lithium groups of 8 years. Because theCorrelation of age and peak prolactin response to intravenous L-tryptophan in control