Role of NADPH oxidase and iNOS in vasoconstrictor responses of vessels from hypertensive and normotensive rats

Background and purpose: To analyse the influence of hypertension in the modulation induced by inducible NOS (iNOS)derived NO and superoxide anion (O-2*(-)) of vasoconstrictor responses and the sources of O-2*(-) implicated. Experimental approach: Vascular reactivity experiments were performed in segments of aorta from normotensive, Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR); protein and mRNA expressions were respectively measured by western blot and quantitative reverse transcription-polymerase chain reaction and O-2*(-) production was evaluated by ethidium fluorescence. Key results: The contractile responses to phenylephrine (1 nM-30 mu M) and 5-hydroxytryptamine (0.1 - 100 mu M) were greater in aortic segments from SHR than WKY. The selective iNOS inhibitor, 1400W (10 mM), increased the phenylephrine contraction only in WKY segments; however, iNOS protein and mRNA expressions were greater in aorta from SHR than WKY. Superoxide dismutase (SOD, 150Uml(-1)) reduced phenylephrine and 5-hydroxytryptamine responses only in aorta from SHR; the NAD(P) H oxidase inhibitor apocynin (0.3 mM) decreased phenylephrine and 5-hydroxytryptamine responses more in vessels from SHR than WKY. Co-incubation with SOD plus 1400W potentiated the phenylephrine and 5-hydroxytryptamine responses more in segments from SHR than WKY. O-2*(-) production was greater in aorta from SHR than WKY; apocynin abolished this difference. Conclusions and implications: Increased O-2*(-) formation from NADP(H) oxidase in vessels from hypertensive rats contributes to the vasoconstrictor responses and counteract the increase of NO from iNOS and the consequent modulation of these responses.