Improvement of stunned myocardium in dogs with olmesartan, an angiotensin II type 1 receptor antagonist, is independent of type 2 receptors

• Published in: Pharmacology Vol. 82; no. 1; p. 22
• Main Authors: Kano, Seiichiro, Satoh, Kumi, Kaneta, Shigeru, Ichihara, Kazuo
• Format: Journal Article
• Language: English
• Published: Switzerland 01-01-2008
• Subjects: Angiotensin II Type 1 Receptor Blockers - pharmacology; Angiotensin II Type 1 Receptor Blockers - therapeutic use; Angiotensin II Type 2 Receptor Blockers; Animals; Dogs; Female; Hemodynamics - drug effects; Imidazoles - pharmacology; Imidazoles - therapeutic use; Male; Myocardial Contraction - drug effects; Myocardial Reperfusion Injury - drug therapy; Myocardial Reperfusion Injury - physiopathology; Myocardial Stunning - drug therapy; Myocardial Stunning - physiopathology; Myocardium - metabolism; Pyridines - pharmacology; Receptor, Angiotensin, Type 2 - physiology; Tetrazoles - pharmacology; Tetrazoles - therapeutic use
• ISSN: 1423-0313
• DOI: 10.1159/000127364

Olmesartan is a selective angiotensin II type 1 receptor (AT1) antagonist. In pentobarbital-anesthetized open-chest dogs, ischemia/reperfusion was induced by ligating the left anterior descending coronary artery for 20 min and releasing it for 60 min, respectively. The myocardial contraction in the ischemic area decreased and returned towards its pre-ischemic level during reperfusion but incompletely. Olmesartan improved the recovery of myocardial contraction during reperfusion associated with restoration of myocardial ATP. Angiotensin II repelled by AT1 receptors occupied by olmesartan can reach and stimulate the angiotensin II type 2 (AT2) receptors, resulting in some beneficial effects on the ischemic myocardium. In fact, AT2 receptor mRNA was found in the adult dog myocardium. In addition, the plasma level of angiotensin II was significantly increased by olmesartan. PD123319, a selective AT2 receptor antagonist, however, did not modify the effect of olmesartan on the cardiac contraction. The hypertensive response to exogenous angiotensin II was completely inhibited by olmesartan, whereas PD123319 did not abolish the effect of olmesartan. In conclusion, olmesartan protects the ischemic/reperfused heart against ischemic injury through inhibition of AT1 receptors but not indirect activation of AT2 receptors.