L-CITRULLINE CONVERSION TO L-ARGININE IN SPHENOPALATINE GANGLIA AND CEREBRAL PERIVASCULAR NERVES IN THE PIG

The presence of nitric oxide synthase (NOS), argininosuccinate synthet ase (ASS), and argininosuccinate lyase (ASL) and their coexistence wit h NADPH-diaphorase (NADPHd), a marker for NOS, in the porcine sphenopa latine ganglia (SPG), pial veins, and the anterior cerebral arteries w as examined using immunohistochemical and histochemical staining techn iques. NOS-immunoreactive (I), ASS-I, and ASL-I fibers were found in p ial veins and the anterior cerebral arteries. NOS, ASS, and ASL immuno reactivities were also found in neuronal cell bodies in the SPG. Almos t all neuronal cell bodies in the SPG and nerve fibers in pial veins a nd the anterior cerebral arteries that were reactive to ASS, ASL, and NOS were also stained positively with NADPHd, suggesting that ASS, ASL , and NOS were colocalized in the same neurons in the SPG and perivasc ular nerves. With the use of in vitro tissue bath techniques, L-citrul line but not D-citrulline reversed inhibition of neurogenic vasodilati on in isolated porcine pial veins produced by NOS inhibitors such as N -G-nitro-L-arginine methyl ester. In the presence of L-aspartate, L-ar ginine was synthesized from L-citrulline in homogenates of SPG and end othelium-denuded cerebral arteries and pial veins. These results provi de evidence indicating that perivascular nerves in pial veins like cer ebral arteries can convert L-citrulline to L-arginine for synthesizing nitric oxide. The conversion is most likely via an argininosuccinate pathway.