Effects of brief and prolonged ischemia on eicosanoid synthesis in dog and rat hearts

We compared the effects of brief and prolonged myocardial ischemia on tissue prostaglandin synthesis. Regional ischemia was induced in dogs and maintained for 5 or 30 minutes. Isolated rat hearts were subjected to global ischemia in a working heart preparation for periods of 5 or 20 minutes. De novo synthesis of prostaglandins PGE₂and PGF_2αwas measured in endocardial and epicardial explants from hearts subjected to transient ischemia. After 5 minutes of coronary ligation, PGE₂production by the ischemic canine endocardium increased by 68%, compared with non-ischemic tissue, and PGF_2αlevels rose by 29%. In isolated rat hearts, 5-minute ischemia increased endocardial rate of PGE₂synthesis (13.2±1.7 pmol/g/h, as compared with 6.7±0.5 under normoxic conditions). Ischemic stimulation of eicosanoid production by the endocardium was no longer apparent after 30-minute regional or 20minute global ischemia. In contrast, the epicardium showed significant changes only after 30-minute ischemia and only with respect to PGF_{2 α}(12.0±6.2 in the ischemic vs 7.1±3.2 pmol/g/h in the non-ischemic tissue). Ischemia-induced differences in prostaglandin production were attenuated in the presence of arachidonic acid or aspirin. We conclude that brief ischemia evokes transient but significant changes in prostaglandin synthesis which are independent of species and of the experimental model. These alterations are marked in the endocardial but not in the epicardial zone.