The K ATP channel blocker HMR 1883 does not abolish the benefit of ischemic preconditioning on myocardial infarct mass in anesthetized rabbits

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Abstract
Previous experimental studies showed that the benefit of ischemic preconditioning (IPC) is abolished by KATP channel blockade with glibenclamide. However, the newly discovered KATP channel blocker HMR 1883 (1-[[5-[2-(5-chloro-o-anisamido)ethyl]-methoxyphenyl]sulfonyl]-3-methylthiourea) shows marked antifibrillatory activity in the dose range of 3 mg/kg to 10 mg/kg i.v. in various experimental models without affecting blood glucose levels. In order to investigate in a head to head comparison glibenclamide and HMR 1883 with respect to their influence on IPC, experiments were performed in rabbits with ischemia-reperfusion using myocardial infarct mass as final read out. Male New Zealand White rabbits (2.6–3.0 kg) were subjected to 30-min occlusion of a branch of the left descending coronary artery (LAD) followed by 2-h reperfusion. For IPC experiments the LAD was additionally occluded for two periods of 5 min, each followed by 10-min reperfusion, before the long-term ischemia. Infarct mass was evaluated by TTC staining and expressed as a percentage of area at risk. Rabbits (n=7/group) were randomly selected to receive (i.v.) saline vehicle 5 min prior to the 30-min occlusion period in infarct studies without IPC or to receive glibenclamide (0.3 mg/kg) or HMR 1883 (3 mg/kg) in IPC experiments, these substances being given 5 min prior to the first preconditioning or 5 min prior to the long-term ischemia of 30 min. Myocardial risk mass as a percentage of left ventricular mass did not differ between groups. The same was true for the ratio of left ventricular mass to 100 g body weight. Myocardial infarct mass as a percentage of the area at risk in the saline vehicle group without IPC was 41±3%. Whereas glibenclamide significantly increased infarct mass (from 41±3% to 55±4%), HMR 1883 did not affect it. IPC reduced infarct mass from 41±3% to 21±4% (P P50) was reduced from 103±3 ms under normoxic conditions to 82±2 ms, 5 min after ischemia in the absence of drugs. This ischemia-induced shortening of the MAP was prevented by both HMR 1883 (MAP50 103±3 ms) and glibenclamide (MAP50 106±3 ms). In conclusion, although both KATP channel blockers prevented ischemia-induced shortening of MAP, HMR 1883 did not abolish the beneficial effects of IPC on myocardial infarct mass in rabbits, whereas glibenclamide totally reversed this cardioprotective effect of IPC. This suggests that the sarcolemmal ATP-sensitive potassium channels are not involved in the mechanism of IPC.

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