Angiotensin II increases neurogenic nitric oxide metabolism in mesenteric arteries from hypertensive rats

We investigated, in mesenteric arteries from hypertensive rats (SHR), the possible changes in neurogenic nitric oxide (NO) release produced by angiotensin II (AII), and the possible mechanisms involved in this process. In deendothelialized segments the NO synthase inhibitor N(G)-nitro-L-arginine (L-NAME, 10 microM) increased the contractions caused by electrical field stimulation (EFS, 200 mA, 0.3 ms, 1-16 Hz, for 30 s). AII (0.1 nM) enhanced the response to EFS, which was unmodified by the subsequent addition of L-NAME. The AII antagonist receptor saralasine (0.1 microM) prevented the effect of AII, and the subsequent addition of L-NAME restored the contractile response. SOD (25 u/ml) decreased the reponse to EFS and the subsequent addition of L-NAME increased this response. AII did not modify the decrease in EFS response induced by SOD, and the addition of L-NAME increased the response. None of these drugs altered the response to exogenous noradrenaline (NA) or basal tone except SOD, which increased the basal tone, an effect blocked by phentolamine (1 microM). In arteries pre-incubated with [3H]-NA, AII did not modify the tritium efflux evoked by EFS, which was diminished by SOD. AII did not alter basal tritium efflux while SOD significantly increased it. These results suggest that EFS of SHR mesenteric arteries releases neurogenic NO, the metabolism of which is increased in the presence of AII by the generation of superoxide anions.