Ischaemic preconditioning does not protect hypertrophied myocardium against ischaemia
Objectives. Because ischaemic preconditioning elicits a potent endogenous protective mechanism against the development of myocardial infarction, it is important to explore its utilisation in clinical situations. The aim of this study was to examine whether the myocardium of rats with genetic hypertension could be protected by ischaemic preconditioning. Methods. Male New Zealand genetically hypertensive rats (GH-Wistar-derived) and normotensive Wistar controls (WAG-Wistar-derived), aged 12 months, were used. Isolated perfused hearts were preconditioned by 3 periods of 5 minutes' global ischaemia, interspersed with 5 minutes' reperfusion, and subsequently subjected to 25 minutes' global ischaemia, followed by 30 minutes' reperfusion. Results. Heart and body mass were significantly higher in GH rats. Although the heart/body mass ratios of GH rats were higher than those of WAG rats, the difference was not significant. The reperfusion coronary flow pattern during the preconditioning protocol differed markedly between the 2 groups. Only normotensive WAG hearts demonstrated protective effects of preconditioning on post-ischaemic function and tissue creatine phosphate content, while the GH hearts could not be preconditioned. Conclusions. An explanation for the failure of preconditioning in GH hearts is not yet available. The data caution against implementation of preconditioning in patients with angina pectoris and left ventricular hypertrophy.