Selective inhibition of neuronal nitric oxide synthase fails to alter the resting tension and the relaxant effect of bradykinin in isolated rat middle cerebral arteries.

: The role of the neuronal isoform of the nitric oxide (NO) synthase (nNOS) in the regulation of the cerebrovascular tone was studied in vitro. Selective inhibition of nNOS by 7-nitro indazole monosodium salt (7-NINA) failed to alter the resting tension and the relaxant effect of bradykinin in isolated rat middle cerebral arteries. These results indicate that 1./ 7-NINA is selective for nNOS and 2./ cerebrovascular nNOS is involved neither in the resting NO production nor in the mediation of the relaxant effect of bradykinin. Therefore, nNOS-derived NO that contributes to the maintenance of the resting cerebral blood flow in vivo appears to be released from neurons and/or glial cells.