A modified citrulline assay of NOS activity in rat brain homogenates does not detect direct effects of halothane on the kinetics of NOS activity

An improved citrulline radioassay of nitric oxide synthase (NOS) activity was developed to study the direct effects of the volatile anesthetic (VA) halothane on the enzyme kinetics of neuronal NOS derived from different regions of the rat central nervous system (CNS). The V(max) of NOS in both soluble cytosolic and membrane bound particulate fractions varied across regions with greatest activity in the cerebellum and least in the spinal cord. In contrast, the K(m) was not different across regions or in the cytosolic and particulate fractions. Halothane at 0.5, 1, 2 or 3% delivered concentration had no effect on either kinetic parameter of NOS in any of the regions studied indicating that the VAs have no direct effects on NOS activity.