Association between plasma nitric oxide metabolites levels and negative symptoms of schizophrenia: a pilot study

Nitric oxide (NO) is involved in pathophysiology of psychiatric disorders such as depression and schizophrenia. We hypothesize that plasma levels of NO and its metabolites (NO(x)) are decreased in patients with schizophrenia. To examine the hypothesis, we compared plasma NO(x) levels between 30 schizophrenic patients (M/F: 18/12, age: 38 +/- 15 years) and age- and sex-matched 30 healthy controls (M/F: 18/12, age: 41 +/- 19 years), and we also examined the effects of risperidone on plasma NO(x) levels in schizophrenic patients. The baseline plasma NO(x) levels were significantly lower in the schizophrenia group (1.85 +/- 0.70 microM) than those in control group (3.37 +/- 2.27 microM). A significantly negative correlation was found between plasma NO(x) levels and PANSS-N scores before risperidone administration (rho = -0.385, p = 0.0416). Treatment with risperidone significantly increased the plasma NO(x) levels by 8 weeks (before; 1.85 +/- 0.70 microM, after; 2.25 +/- 1.00 microM, p = 0.0491). These results suggest that NO might be one of the candidates factors which are associated with the pathophysiology of negative symptoms of schizophrenia.