Objectives: Angiotensin (Ang) II type 1 (AT1) receptors mediate the majority of cardiovascular effects of Ang II, whereas the role of type 2 (AT2) receptors is still controversial. The present study, therefore, investigated regional hemodynamic responses mediated by AT2 receptors in humans.
Methods: Studies were performed in 20 healthy individuals (eight men; mean age 37 ± 3 years) through intra-arterial infusion of agonists and antagonists of Ang II receptors by use of strain-gauge plethysmography.
Results: Selective blockade of either AT1 or AT2 receptors by telmisartan or PD 123319, respectively, resulted in mild forearm blood flow increase (15 ± 5% and 10 ± 4, respectively; both P > 0.05); combined AT1 and AT2 receptor antagonism, however, was associated with greater vasodilator response (25 ± 5%; P = 0.02). This effect was unrelated to increased nitric oxide activity, being unaffected (27 ± 5%; P = 0.65) by a ‘ nitric oxide clamp’ (coinfusion of the nitric oxide synthase inhibitor L-NMMA and the nitric oxide donor sodium nitroprusside). Graded doses of Ang II induced a progressive vasoconstrictor response that was blunted not only by telmisartan, but also by PD 123319 and by the combination of PD 123319 and telmisartan (all P < 0.001 vs. Ang II alone). AT2 receptor stimulation by CGP 42112A resulted in a dose-dependent vasodilation (P < 0.001 vs. baseline), that was abolished by the nitric oxide clamp and by PD 123319 (both P < 0.001 vs. CGP 42112A alone).
Conclusion: In the human forearm, vasoconstrictor AT2 receptors coexist with AT2 receptors mediating nitric oxide-dependent vasodilation. These findings suggest that imbalance between these opposing hemodynamic actions may affect vascular homeostasis and foster further investigation about the role of AT2 receptors in human disease.