Angiotensin IV receptor-mediated activation of lung endothelial NOS is associated with vasorelaxation

The hexapeptide angiotensin (ANG) TV, a metabolic product of ANG IT, has been reported to play a functional role in the regulation of blood flow in extrapulmonary tissues. Here, we demonstrate that ANG IV-specific (AT(4)) receptors are present in porcine pulmonary arterial endothelial cells (PAECs) and that the binding of ANG IV to AT(4) receptors can be blocked by its antagonist divalinal ANG IV but not by the ANG II-, AT(1)-, and AT(2)-receptor blockers [Sar(1),Ile(8)]ANG II, losartan, and PD-123177, respectively. ANG TV significantly increased endothelial cell constitutive nitric oxide synthase (ecNOS) activity (P < 0.05) as well as cellular cGMP content (P < 0.001). Western blot analysis revealed that ecNOS protein expression was comparable in control and ANG IV-stimulated cells. Divalinal ANG TV but not [Sar(1),Ile(8)]ANG IT, losartan, or PD-123177 inhibited the ANG II- and ANG IV-stimulated increases in ecNOS activity and cGMP content in PAECs. Incubation in the presence of N-nitro-L-arginine methyl ester (L-NAME) or methylene blue but not of indomethacin significantly diminished ANG IV-stimulated as well as basal levels of cGMP (P < 0.001). Similarly, in situ studies with precontracted porcine pulmonary arterial rings showed that ANG IV caused an endothelium-dependent relaxation that was blocked by L-NAME or methylene blue. Collectively, these results demonstrate that ANG IV binds to AT(4) receptors, activates ecNOS by posttranscriptional modulation, stimulates cGMP accumulation in PAECs, and causes pulmonary arterial vasodilation, suggesting that ANG TV plays a role in the regulation of blood how in the pulmonary circulation.