Myocardial and coronary endothelial protective effects of acetylcholine after myocardial ischaemia and reperfusion in rats: role of nitric oxide

Abstract

1 Recent experiments suggest that acetylcholine (ACh) may exert myocardial protective effects during ischaemia (I) and reperfusion (R). The present study was designed (i) to assess whether ACh limits infarct size and protects coronary endothelial cells in a rat model of I and R, (ii) to evaluate the role of ATP-sensitive potassium (KATP) channels and nitric oxide (NO) in the beneficial effect of ACh (iii) to evaluate whether the protective effect of ACh also extends to coronary endothelial cells and (iv) to assess whether ACh contributes to the beneficial effect of preconditioning. 2 Anaesthetized rats were subjected to 20 min I (left coronary artery occlusion) and 2 h of R. Infarct size was assessed by triphenyltetrazolium (TTC) staining and expressed as a % of the area at risk (India ink injection). Vascular studies were performed on 1.5-2 mm coronary segments (internal diameter 250-300 pm) removed distal to the site of occlusion and mounted in wire myographs. 3 ACh limited infarct size (from 59+3 to 26+5%, P<0.01), and this was prevented by atropine (46+7%; P<0.05 vs ACh), but not by the inhibitor of KATP channels, glibenclamide (29±8%). The inhibitor of NO synthesis N0-nitro L-arginine did not affect infarct size (54+5%) but abolished the beneficial effect of ACh (59 8%; P<0.05 vs ACh), whereas the NO donor 3-morpholinosydnonimine-N-ethylcarbamide (SIN-I limited infarct size to the same extent as ACh (28 ± 6%). Preconditioning also limited infarct size (5 2%, P< 0.01 vs control), and this was not affected by atropine (6 ± 2%). I and R induced a significant decrease in the endothelium-dependent relaxations of isolated coronary arteries to ACh (maximal response: sham: 58+4; I/R: 25±5%; P<0.01) and this dysfunction was prevented by prior in vivo treatment with ACh (55+7%; P<0.01 vs I/R) or (SIN-1 50+5%; P<0.05 vs I/R). 4 Thus, in the rat model, ACh is able to stimulate potent endogenous protective mechanisms during I and R, which are evident both at the level of myocardial and coronary endothelial cells, and appear entirely mediated through the production of NO. Pharmacological stimulation of this endogenous protective mechanism may constitute a new approach in the treatment of acute myocaridal ischaemia.

Protection of Myocytes From Hypoxia-Reoxygenation Injury by Nitric Oxide Is Mediated by Modulation of Transforming Growth Factor-β 1

“…Despite a small increase in nitrite levels in myocardial tissues, exogenous NO donors have been shown to protect myocardial tissues from H-R injury. 14,15 The protective effect of exogenous NO donors may relate to chelation and neutralization of superoxide anions and other ROS, 18,23 which are released during H-R. The present study clearly shows a myocyte-protective effect of two different NO donors, SIN-1 and NTG.…”

Coronary endothelial dysfunction after ischemia and reperfusion: a new therapeutic target?

“…Indeed, endogenous stimulation of eNOS (for example by acetylcholine) may exert marked endothelial protective effects after ischemia and reperfusion (34). Moreover, our experiments on cultured cells demonstrated an increase of the nuclear factor AP-1 in the endothelial cell nucleus after preconditioning (27), and this may be correlated to the increased level of eNOS mRNA, since AP-1 is responsible for the enhanced expression and activity of eNOS (35).…”

The mechanism of cardioprotection by S‐nitrosoglutathione monoethyl ester in rat isolated heart during cardioplegic ischaemic arrest

“…Physiological responses of ventricular myocytes to muscarinic and fl-adreno- (Hartman et al, 1994;Richard et al, 1995;Zhu et al, 1995). Conflicting experimental results have been obtained with -NO synthase inhibitors during ischaemia.…”