Nitric oxide and neopterin in bipolar affective disorder.

Background: There is an increasing interest in the role of nitric oxide (NO) and pterines in the pathophysiology of neuropsychiatric disorders. The results so far show an inconsistent pattern. Methods: In the present study, neopterin and a measure of NO synthesis in plasma of symptomatic and euthymic bipolar affective patients were compared to those of patients with a major depression and healthy controls. As an index of NO synthesis, the ratio of the amino acids citrulline and arginine (Cit-Arg ratio) was calculated. Neopterin is a bypass product in the synthesis of tetrahydrobiopterin, which is a cofactor of NO synthase. Results: The results indicate that both neopterin and the Cit-Arg ratio are decreased in bipolar affective patients, irrespective of their symptomatic status. In addition, an association between the values of the Cit-Arg ratio and the neopterin level was observed, which is suggestive for a low tetrahydrobiopterin activity. Conclusion: NO formation may be endangered in bipolar affective disorder.