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It has been reported that isolated rat heart myocytes and cardiac mesenchymal cells convert arachidonic acid mainly into three types of prostaglandins (PGs): PGE2, PGF2 alpha, and PGI2. In addition, we have demonstrated that fresh atrial slices of patients with heart-valve disease contain appreciable quantities of PGE2 and PGF2 alpha. However, there have been no reports on the subcellular localization of the prostaglandin system in heart muscle tissue. The present study was performed to define the distribution of PGE2 in mitochondrial, microsomal, and cytosolic fractions, isolated by differential centrifugation from homogenates of fresh normal rat atrium and ventricle slices. In addition, we determined whether differences exist in PGE2 levels between atrial subcellular fractions and those of ventricular fractions. The results showed that PGE2 was located mainly in the high-speed cytosolic supernatant fraction of the heart homogenates analyzed. Furthermore, PGE2 concentrations (ng/mg protein) were significantly higher in fractions obtained from atrial than those of ventricular tissue.

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