Abstract
Objective: Several studies showed that nitric oxide (NO) plays role in the pathophysiology of bipolar disorder (BD). Arginase might be important in the regulation of NO since both arginase and NO synthase use L-arginine as a common substrate. Although studies generally found increased levels of NO in BD, the picture is less clear for arginase activity. The present study aimed to investigate arginase activity together with NO levels in patients with bipolar disorder-depressed episode (BD-DE) in a prospective design.
Method(s): 33 BD-DE patients, diagnosed according to DSM-IV, and 33 age, gender and smoking satus matched healthy volunteer controls were included. Serum NO levels and arginase activities of the patient group were measured before any treatment and compared to that of controls. The patients were then allowed for episode specific naturalistic treatments including pharmacotherapy and electroconvulsive therapy when indicated. NO and arginase levels were evaluated on the 30th day of treatment and clinical outcome was measured by the Hamilton Depression Scale.
Results: Pretreatment NO levels and arginase activities of the patients were significantly higher than the healthy volunteers (p<0.001 in both). After 30 days of treatment, both NO levels and arginase activities were decreased (p<0.001), and reached to the volunteersÂ’ levels. There was no significant correlation between plasma arginase and NO levels in either at the beginning or 30th day evaluations.
Conclusion(s): Interaction between arginase and NO synthase does not seem to be as simple as just competing for a common substrate. Treatment modalities, clinical improvement of the depressive episode or other factors might be important in the normalization of NO levels and arginase activity.

Key words: Bipolar disorder, nitric oxide, arginase, depressive episode, treatment