Preconditioning against infarction in the rat heart does not involve a pertussis toxin sensitive G protein.

OBJECTIVE

Adenosine receptor antagonists and pertussis toxin both block the anti-infarct effect of preconditioning in rabbit heart. Because adenosine receptor blockers were found to have no effect against preconditioning in rat heart, a study was performed to test whether ribosylating G proteins with pertussis toxin would block the protection.

METHODS

A branch of the left coronary artery was occluded for 30 min and reperfused for 2 h to produce infarction in open chest rats. Infarct size was assessed by tetrazolium staining. Pertussis toxin was given 48 h before surgery. Preconditioned rats experienced three cycles of 5 min regional ischaemia and 5 min reperfusion before the 30 min occlusion.

RESULTS

Four groups of rats were studied. Non-treated control rats had 68.8(SEM 2.2)% infarction of the risk zone and preconditioning reduced this to 32.0(6.5)%. Pertussis toxin completely eliminated the G protein mediated bradycardia caused by intravenous acetylcholine or adenosine infusion. Pertussis toxin treatment had no effect on infarct size in non-preconditioned rats [60.9(4.2)% infarction]. Preconditioning the pertussis toxin treated heart reduced infarction to 21.3(5.6)%, an amount comparable to that seen in non-treated rats. Arrhythmias during the 30 min ischaemia were reduced in preconditioned hearts and this protection was not altered by pertussis toxin treatment.

CONCLUSIONS

Preconditioning against either infarction or arrhythmias in the rat does not appear to involve a pertussis toxin sensitive G protein.