The subtype 2 (AT2) angiotensin receptor mediates renal production of nitric oxide in conscious rats

Abstract

The angiotensin AT2 receptor modulates renal production of cyclic guanosine 3',5'-monophosphate (cGMP; J. Clin. Invest. 1996. 97:1978-1982). In the present study, we hypothesized that angiotensin II (Ang II) acts at the AT2 receptor to stimulate renal production of nitric oxide leading to the previously observed increase in cGMP. Using a microdialysis technique, we monitored changes in renal interstitial fluid (RIF) cGMP in response to intravenous infusion of the AT2 receptor antagonist PD 123319 (PD), the AT1 receptor antagonist Losartan, the nitric oxide synthase (NOS) inhibitor nitro--arginine-methyl-ester (-NAME), the specific neural NOS inhibitor 7-nitroindazole (7-NI), or Ang II individually or combined in conscious rats during low or normal sodium balance. Sodium depletion significantly increased RIF cGMP. During sodium depletion, both PD and -NAME caused a similar decrease in RIF cGMP. Combined administration of PD and -NAME decreased RIF cGMP to levels observed with PD or -NAME alone or during normal sodium intake. During normal sodium intake, Ang II caused a twofold increase in RIF cGMP. Neither PD nor -NAME, individually or combined, changed RIF cGMP. Combined administration of Ang II and either PD or -NAME produced a significant decrease in RIF cGMP compared with that induced by Ang II alone. Combined administration of Ang II, PD, and -NAME blocked the increase in RIF cGMP produced by Ang II alone. During sodium depletion, 7-NI decreased RIF cGMP, but the reduction of cGMP in response to PD alone or PD combined with 7-NI was greater than with 7-NI alone. During normal sodium intake, 7-NI blocked the Ang II-induced increase in RIF cGMP. PD alone or combined with 7-NI produced a greater inhibition of cGMP than did 7-NI alone. During sodium depletion, 7-NI (partially) and -NAME (completely) inhibited RIF cGMP responses to -arginine. These data demonstrate that activation of the renin- angiotensin system during sodium depletion increases renal nitric oxide production through stimulation by Ang II at the angiotensin AT2 receptor. This response is partially mediated by neural NOS, but other NOS isoforms also contribute to nitric oxide production by this pathway.