CHANGES IN PLASMA PROLACTIN DURING SSRI TREATMENT - EVIDENCE FOR A DELAYED INCREASE IN 5-HT NEUROTRANSMISSION

We studied the effect of the selective serotonin reuptake inhibitor (S SRI), paroxetine, on basal plasma prolactin concentrations in 11 healt hy subjects. Subjects were tested before paroxetine, and after 1 and 3 weeks of treatment (20mg daily). On each test occasion prolactin leve ls were sampled before and following administration of a placebo capsu le, for a total of 4h. After 3 weeks paroxetine treatment plasma prola ctin levels were significantly higher than those seen either pre-treat ment or after 1 week of treatment. In contrast, 1 week of paroxetine t reatment did not significantly increase prolactin concentrations over pre-treatment values. Plasma concentrations of paroxetine did not diff er between 1 and 3 weeks of treatment. The secretion of plasma prolact in is, in part, under the tonic regulation of serotonergic pathways an d the present results therefore support animal experimental data sugge sting that SSRIs produce a delayed increase in some aspects of brain s erotonin neurotransmission.