Role of endothelium-derived relaxing factor in cerebral circulation: large arteries vs. microcirculation

This study examined the hypothesis that formation of endothelium-derived relaxing factor (EDRF) in the brain has a greater influence on basal tone in large arteries than arterioles. Diameters of the basilar artery and its branches and of arterioles on the cerebrum were measured through cranial windows in anesthetized rats. Under control conditions, topical application of NG-monomethyl-L-arginine (L-NMMA), which inhibits formation of EDRF or nitric oxide (NO) from L-arginine, produced concentration-related constriction that was dependent on initial vessel diameter. Large arteries [diameter = 275 +/- 10 microns (mean +/- SE)] constricted by 10.4 +/- 0.8% in response to 10(-5) M L-NMMA. In contrast, arterioles (62 +/- 6 microns) constricted by only 3.7 +/- 0.6% (P less than 0.01 vs. large arteries), regardless of brain region. U-46619 produced similar constriction of large arteries and arterioles, which indicates that reduced responses to L-NMMA in arterioles is not due to impaired constrictor capacity. Sodi...