Nitric oxide synthase activity in brain regions and spinal cord of mice and rats: kinetic analysis.

Nitric oxide synthase (NOS) activity was determined by the rate of conversion of [3H]arginine to [3H]citrulline in brain regions (midbrain, hypothalamus, cerebellum, hippocampus, corpus striatum, cortex, pons-medulla and amygdala) and spinal cord of male Swiss Webster mice and male Sprague-Dawley rats. In mice, high activity of NOS was found in cerebellum, hypothalamus and midbrain; intermediate activity in pons-medulla, hippocampus, amygdala, corpus striatum and cortex; and low activity in the spinal cord. In rat, highest activity of NOS was observed in cerebellum followed in decreasing order by midbrain, hypothalamus, cortex, striatum, pons-medulla, hippocampus and spinal cord. In all tissues, NOS activity was higher in rat than in mouse. Analysis of the Eadie-Hofstee plot indicated that the Vmax and Km values of the enzyme in cortex and cerebellum of rats were higher than in mouse tissues. These studies show differential distribution of NOS activity in mouse and rat brain regions and spinal cord and higher activity of NOS in rat brain regions and spinal cord compared to mouse tissues.