LIPID-PEROXIDATION, ARACHIDONIC-ACID AND PRODUCTS OF THE LIPOXYGENASEPATHWAY IN ISCHEMIC PRECONDITIONING OF RAT-HEART

Objective: Preconditioning with brief intermittent periods of ischaemi a is known to provide protection against ischaemic injury. It has been suggested that myocardial ischaemia also activates phospholipase A(2) , which releases arachidonic acid from phospholipids. In the present s tudy the possible role of phospholipid peroxidation, arachidonic acid and products of the lipoxygenase pathway in cellular mechanisms of isc haemic preconditioning was examined. Methods: Isolated, buffer-perfuse d rat hearts were freeze-clamped at the end of preconditioning (a cycl e of 5 min global ischaemia +5 min reperfusion) and at the end of 30 m in global ischaemia and analysed for non-esterified fatty acids and fa tty acids in the 2-position of phospholipid. In a separate set of expe riments, hearts pretreated with a lipoxygenase inhibitor, nordihydrogu aiaretic acid (NDGA), were subjected to 30 min regional ischaemia and 120 min reperfusion. Infarct size was determined by tetrazolium staini ng and the ischaemic risk zone with fluorescent particles. Results: My ocardial levels of arachidonic as well as of linoleic and docosahexaen oic acid were significantly elevated by preconditioning. Also, the lev el of peroxidized polyunsaturated fatty acids (measured as hydroxy con jugated dienes) in myocardial phospholipid was significantly increased : 101.4 +/- 16.8 nmol/g versus 51.2 +/- 7.3 nmol/g tissue dw in the co ntrol group, p < 0.05. Pre-treatment of hearts with 5 mu M NDGA blocke d the infarct limiting effect of preconditioning: infarct size was 37. 4 +/- 6.4% of risk zone in control, 9.0 +/- 0.9% in the preconditionin g group and 27.7 +/- 3.8% in the preconditioning + NDGA group (p < 0.0 5 vs. IP, n.s. vs. control). Conclusion: Our findings provide evidence for the involvement of phospholipase A(2) and lipoxygenase derived li pid second messengers in ischaemic preconditioning of the isolated rat heart. (C) 1998 Elsevier Science B.V.