Effect of classic preconditioning and diazoxide on endothelial function and O2- and NO generation in the post-ischemic guinea-pig heart.
OBJECTIVE
A hypothesis was tested that a reaction product between superoxide (O2-) and nitric oxide (NO) mediates post-ischemic coronary endothelial dysfunction that ischemic preconditioning (IPC) protects the endothelium by preventing post-ischemic cardiac O2- and/or NO formation, and that the opening of the mitochondrial ATP-dependent potassium channel (mKATP) plays a role in the mechanism of IPC.


METHODS
Langendorff-perfused guinea-pig hearts were subjected either to 30 min global ischemia/30 min reperfusion (IR) or were preconditioned prior to IR with three cycles of either 5 min ischemia/5 min reperfusion or 5 min infusion/5 min wash-out of mKATP opener, diazoxide (0.5 microM). Coronary flow responses to acetylcholine (ACh) and nitroprusside were used as measures of endothelium-dependent and -independent vascular function, respectively. Myocardial outflow of O2- and NO, and functional recoveries were followed during reperfusion.


RESULTS
IR impaired the ACh response by approximately 60% and augmented cardiac O2- and NO outflow. Superoxide dismutase (150 U/ml) and NO synthase inhibitor, l-NMMA (100 microM) inhibited the burst of O2- and NO, respectively, and afforded partial preservation of the ACh response in IR hearts. NO scavenger, oxyhemoglobin (25 microM), afforded similar endothelial protection. IPC and diazoxide preconditioning attenuated post-ischemic burst of O2-, but not of NO, and afforded a complete endothelial protection. Diazoxide given after 30-min ischemia increased the O2- burst and was not protective. The effects of IPC and diazoxide preconditioning were not affected by HMR-1098 (25 microM), a selective blocker of plasmalemmal KATP, and were abolished by glibenclamide (0.6 microM) and 5-hydroxydecanoate (100 microM), a nonselective and selective mK(ATP) blocker, respectively. 5-Hydroxydecanoate produced similar effects, whether it was given as a continuous treatment or was washed out prior to IR.


CONCLUSIONS
The results suggest that in guinea-pig heart: (i) a reaction product between O2- and NO mediates the post-ischemic endothelial dysfunction; (ii) the mK(ATP) opening serves as a trigger of the IPC and diazoxide protection; and (iii) the mK(ATP) opening protects the endothelium in the mechanism that involves the attenuation of the O2- burst at reperfusion.
Beresewicz
Andrzej
A
Department of Clinical Physiology, Medical Centre of Postgraduate Education, 01-813 Warsaw, Poland. aberesew@cmkp.edu.pl
Maczewski
Michal
M
Duda
Monika
M
D000818:Animals; D001549:Benzamides / Q000627:therapeutic use; D003652:Decanoic Acids / Q000627:therapeutic use; D003981:Diazoxide / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism; D005905:Glyburide / Q000627:therapeutic use; D006168:Guinea Pigs; D006880:Hydroxy Acids / Q000627:therapeutic use; D019157:Ischemic Preconditioning, Myocardial; D017202:Myocardial Ischemia / Q000188:drug therapy* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D010477:Perfusion; D026902:Potassium Channel Blockers / Q000627:therapeutic use; D015221:Potassium Channels / Q000187:drug effects*
D001549:Benzamides; D003652:Decanoic Acids; D005609:Free Radicals; D006880:Hydroxy Acids; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D009569:Nitric Oxide; C052853:5-hydroxydecanoic acid; C410297:HMR 1098; D003981:Diazoxide; D005905:Glyburide