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NOS expression and activity in cerebral resistance arteries: Effects of age and exercise training

We have previously shown that endothelium‐dependent vasodilation to acetylcholine (ACh) is preserved in cerebral resistance arteries from aged rats; however, the role of specific isozymes of nitric oxide synthase (NOS) in mediating dilation to ACh changes with age and exercise training. In the present study, we investigated the effects of age and exercise training on expression and activity of NOS isoforms. Young (4 months) and old (24 months) male Fischer‐344 rats underwent exercise training or remained sedentary for 10 weeks. Posterior communicating arteries (PCoA) were isolated for assessment of ACh‐stimulated NO production and protein levels of NOS isozymes. ACh‐stimulated NO production was similar in PCoA from young and old rats. Treatment with aminoguanidine, an inhibitor of iNOS significantly reduced NO production in PCoA from young but not old rats; however, iNOS protein was not detectable in PCoA from rats in any of the groups. Although protein levels for endothelial NOS (eNOS) and neuronal NOS (nNOS) were not altered by age or exercise training; calcium‐free production of NO was significantly lower in PCoA from old rats. These data indicate that NOS activity differs in PCoA from young and old rats; however, alterations of NO production that occur with age and training are likely related to changes in NOS regulatory mechanisms rather than changes in enzyme expression.