Ageing affects nitric oxide synthase, cyclooxygenase and oxidative stress enzymes expression differently in mesenteric resistance arteries.

1 Our aim was to study the role of nitric oxide (NO) and arachidonic acid pathways in the alpha(1)-adrenoceptor-mediated vasoconstriction in mesenteric resistance arteries from 3--4 and 22 to 23-month-old Sprague-Dawley rats. 2 The expression of NO synthase (NOS), cyclooxygenase (COX) isoforms, soluble guanylate cyclase, superoxide dismutase and the NAD(P)H oxidase subunits p22(phox) and p 47(phox) were determined. 3 The N(G)-nitro-l-arginine methyl ester, a non-selective NOS inhibitor, shifted to the left but indomethacin and NS 398, non-selective and selective COX-2 inhibitors, shifted to the right the concentration-response curve for the vasoconstriction by phenylephrine in both age groups. 4 Ageing up-regulated endothelial NOS and p22(phox) expression but did not modify COX, soluble guanylate cyclase, superoxide dismutase and p 47(phox) expression. 5 These data suggest that the observed enhancement of eNOS protein expression could constitute a compensatory mechanism to counter-regulate a chronic loss of NO possibly through increased superoxide anion production from NAD(P)H oxidase induced by age.