NOS Activity Assay

Nitric oxide in tissue samples was measured by NOS activity by the conversion of radiolabeled arginine-to-citrulline, using a modified NOS activity assay in the absence of additional assay BH4 and in the presence of an arginase inhibitor, as described previously (Cayman Chemical, Ann Arbor, MI, USA).^15,26 For each sample, background was determined by incubation in the presence of N-Nitro-L-arginine (L-NNA) and subtracted from the total counts. A portion of the sample was used for Western blotting.