Substance P in serum and cerebrospinal fluid of depressed patients: No effect of antidepressant treatment

The neuropeptide substance P (SP) and its receptor, the neurokinin receptor-1 (NK-1), have been associated with some aspects of the pathophysiology of depression. There is limited information available about the effects of antidepressant treatment on serum and cerebrospinal fluid (CSF) concentrations of SP. We measured serum levels of SP in 78 depressed patients after a 6-day medication washout period, as well as after 14 and 35 days of antidepressant treatment with either paroxetine or amitriptyline. In 11 patients, SP was determined in CSF both before and after treatment. Eleven healthy male subjects served as controls. Baseline SP concentrations were independent of age, gender and severity of depression. Neither the total group nor subgroups showed significant differences in SP serum concentrations. SP concentrations in CSF did not change significantly in the patients during treatment, but there was a trend for an increase in paroxetine-treated patients. Serum SP concentrations were not related to treatment response or the class of antidepressant administered. Our data do not support the hypothesis that changes in SP levels in serum or CSF are related to antidepressant response.