1054
Cardiovascular Research 1992;26:1054-1062
Blockade of ischaemic preconditioning in dogs by the novel ATP dependent potassium channel antagonist sodium 5-hydroxydecanoate John A Auchampach, Gary J Grover, and Garrett J Gross
S
ingle or multiple brief periods of ischaemia paradoxically limit infarct size after a subsequent more prolonged occlusion.' This phenomenon has been termed ischaemic preconditioning and has been shown to occur in several species including dogs,'" and rabbits.ISi4 Furthermore, there is indirect evidence that it occurs in humans.15 Since the discovery of this phenomenon, there has been a surge of interest as to the mechanism by which preconditioning renders the heart resistant to ischaemia. Recently, strong evidence has been presented which suggests that activation of the adenosine AI receptor triggers the protective effect. This hypothesis is based on studies in which the selective AI antagonist, DPCPX, was shown to block preconditioning in both pigs' and dogs: and R-PIA, a selective AI agonist, was shown to mimic preconditioning in rabbits." These studies clearly implicate the involvement of adenosine in ischaemic preconditioning; however, the subsequent cellular events after AI receptor activation remain unknown, although preliminary evidence suggests that a Gi protein may be a mediator.13 Recently, Kirsch et aZ16 showed in neonatal rat ventricular myocytes that activation of adenosine A1 receptors opens the
ATP dependent potassium channel (KATP)via a Gi protein. Since activation of this channel by either ischaemia or potassium channel openers has been shown to be cardioprotective,17-20 we hypothesised that the KATPchannel may be involved in the mechanism of preconditioning. Indeed, recent results in our laboratory3 support this hypothesis. We found that intravenous administration of glibenclamide, an antagonist of KATPchannels," blocks the beneficial effect of ischaemic preconditioning in anaesthetised dogs. However, in these studies systemic administration of glibenclamide also resulted in a marked reduction in blood glucose, presumably by increasing insulin secretion from the pancreas. Thus it is possible that glibenclamide blocked preconditioning as a result of increased insulin or decreased blood glucose levels and not as a direct result of KATPchannel blockade in the myocyte. Thus the major objective of the present study was to determine whether blocking KATP channels in the myocardium prevents preconditioning in the absence of systemic metabolic effects. To achieve this objective, we gave sodium 5-hydroxydecanoate (5-HD), a new KATP channel antagonist which has the novel effect of blocking the KATPchannel only during ischaemia by competing with the
Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Waterdown Plank Road, Milwaukee, WI 53226, USA: J A Auchampach, G J Gross; Bristol-Myers Squibb, Princeton, New Jersey, USA: G J Grover. Correspondence to Dr Gross.
Downloaded from http://cardiovascres.oxfordjournals.org/ at University of Winnipeg on September 9, 2014
Objective: The aims were (1) to determine if a new ischaemia selective ATP dependent potassium (KATP) channel antagonist, sodium 5-hydroxydecanoate (5-HD), blocks ischaemic preconditioning in dogs; (2) to determine whether a small intracoronary dose of glibenclamide, a classical sulphonylurea KATPchannel antagonist, could block ischaemic preconditioning independent of systemic metabolic effects. Methods: Barbitone anaesthetised dogs were subjected to 60 rnin of left circumflex coronary artery occlusion followed by 5 h of reperfusion. Preconditioning was produced by a single 5 min left circumflex occlusion followed by 10 min of reperfusion prior to the 60 min occlusion period. 5-HD (150 p,gkg-I.min-') or vehicle was given by intracoronary infusion into the ischaemic region over 20 min, beginning 15 min prior to the 60 min occlusion period in the presence or absence of preconditioning. Glibenclamide (3 p,g.kg-'.min-') was given by intracoronary infusion into the left circumflex artery during the 5 rnin preconditioningperiod or during the first 5 rnin of occlusion in preconditioned or non-preconditioned dogs. Transmural myocardial blood flow was measured by radioactive microspheres and infarct size determined by triphenyltetrazolium staining and expressed as a percent of the area at risk. Results: There were no differences in haemodynamic variables, myocardial blood flow, area at risk, or blood glucose between groups. Infarct size was markedly reduced in preconditioned dogs compared to control animals, at 7(SEM 2)% v 29(4)%, p
Cardiovascular Research 1992;26:1054-1062
Blockade of ischaemic preconditioning in dogs by the novel ATP dependent potassium channel antagonist sodium 5-hydroxydecanoate John A Auchampach, Gary J Grover, and Garrett J Gross
S
ingle or multiple brief periods of ischaemia paradoxically limit infarct size after a subsequent more prolonged occlusion.' This phenomenon has been termed ischaemic preconditioning and has been shown to occur in several species including dogs,'" and rabbits.ISi4 Furthermore, there is indirect evidence that it occurs in humans.15 Since the discovery of this phenomenon, there has been a surge of interest as to the mechanism by which preconditioning renders the heart resistant to ischaemia. Recently, strong evidence has been presented which suggests that activation of the adenosine AI receptor triggers the protective effect. This hypothesis is based on studies in which the selective AI antagonist, DPCPX, was shown to block preconditioning in both pigs' and dogs: and R-PIA, a selective AI agonist, was shown to mimic preconditioning in rabbits." These studies clearly implicate the involvement of adenosine in ischaemic preconditioning; however, the subsequent cellular events after AI receptor activation remain unknown, although preliminary evidence suggests that a Gi protein may be a mediator.13 Recently, Kirsch et aZ16 showed in neonatal rat ventricular myocytes that activation of adenosine A1 receptors opens the
ATP dependent potassium channel (KATP)via a Gi protein. Since activation of this channel by either ischaemia or potassium channel openers has been shown to be cardioprotective,17-20 we hypothesised that the KATPchannel may be involved in the mechanism of preconditioning. Indeed, recent results in our laboratory3 support this hypothesis. We found that intravenous administration of glibenclamide, an antagonist of KATPchannels," blocks the beneficial effect of ischaemic preconditioning in anaesthetised dogs. However, in these studies systemic administration of glibenclamide also resulted in a marked reduction in blood glucose, presumably by increasing insulin secretion from the pancreas. Thus it is possible that glibenclamide blocked preconditioning as a result of increased insulin or decreased blood glucose levels and not as a direct result of KATPchannel blockade in the myocyte. Thus the major objective of the present study was to determine whether blocking KATP channels in the myocardium prevents preconditioning in the absence of systemic metabolic effects. To achieve this objective, we gave sodium 5-hydroxydecanoate (5-HD), a new KATP channel antagonist which has the novel effect of blocking the KATPchannel only during ischaemia by competing with the
Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Waterdown Plank Road, Milwaukee, WI 53226, USA: J A Auchampach, G J Gross; Bristol-Myers Squibb, Princeton, New Jersey, USA: G J Grover. Correspondence to Dr Gross.
Downloaded from http://cardiovascres.oxfordjournals.org/ at University of Winnipeg on September 9, 2014
Objective: The aims were (1) to determine if a new ischaemia selective ATP dependent potassium (KATP) channel antagonist, sodium 5-hydroxydecanoate (5-HD), blocks ischaemic preconditioning in dogs; (2) to determine whether a small intracoronary dose of glibenclamide, a classical sulphonylurea KATPchannel antagonist, could block ischaemic preconditioning independent of systemic metabolic effects. Methods: Barbitone anaesthetised dogs were subjected to 60 rnin of left circumflex coronary artery occlusion followed by 5 h of reperfusion. Preconditioning was produced by a single 5 min left circumflex occlusion followed by 10 min of reperfusion prior to the 60 min occlusion period. 5-HD (150 p,gkg-I.min-') or vehicle was given by intracoronary infusion into the ischaemic region over 20 min, beginning 15 min prior to the 60 min occlusion period in the presence or absence of preconditioning. Glibenclamide (3 p,g.kg-'.min-') was given by intracoronary infusion into the left circumflex artery during the 5 rnin preconditioningperiod or during the first 5 rnin of occlusion in preconditioned or non-preconditioned dogs. Transmural myocardial blood flow was measured by radioactive microspheres and infarct size determined by triphenyltetrazolium staining and expressed as a percent of the area at risk. Results: There were no differences in haemodynamic variables, myocardial blood flow, area at risk, or blood glucose between groups. Infarct size was markedly reduced in preconditioned dogs compared to control animals, at 7(SEM 2)% v 29(4)%, p
