Interactions between angiotensin I and acetylcholine on rat left main bronchial rings.

Angiotensin (Ang) II is known to amplified bronchoconstriction induced by acetylcholine (ACh). On the other hand all the components of renin angiotensin system were located on lungs. Contractile effects of Ang I (the precursor of Ang II) and interactions between Ang I and ACh on rat bronchial rings were characterize using angiotensin II type 1 (AT1) receptor antagonist (losartan), angiotensin converting enzyme (ACE) inhibitors (captopril and teprotide) and chymase inhibitor (chymostatin). We found that Ang I has contractile effects and amplified ACh-induced contractions. Blocking of AT1 receptors with 10 mM losartan significantly reduced 10 mM Ang I contractile effects (12.79 +/- 9.59% from 167.62 +/- 8.92%; p<0.05). Pre-treatment with 1 mM teprotide reduced 10 mM Ang I-induced contractions (35.68 +/- 7.83%; p>0.05). Captopril and teprotide only reduced Ang I actions. This suggested that both types of Ang I effects were mediated by AT1 receptors, but possibly conversion of Ang I into Ang II were not significantly dependent by ACE or chymase.