Prostaglandin formation from exogenous precursor in homogenates of human cardiac tissue

The ability of some different components of human cardiac tissue to synthesize prostaglandins (PGs) from exogenous precursor was investigated. Fractions of the cardiac tissue containing either parts of valve cusps and the papillary musculature or some selected tissue components such as myocytes, endocardial elements, endothelial cells and connective tissue were prepared and homogenized. Low-speed supernatants of the various homogenates thus obtained were incubated with [14C]-labelled arachidonate [( 14C]-AA]. [14C]-PGs formed in the incubates were extracted, separated by thin-layer chromatography and quantified using liquid scintillation spectrometry. In the incubates of all the fractions [14C]-AA was converted to [14C]-PGs with a time-dependent yield, most effectively at 3 minutes' incubation time. The "endocardial" and "endothelial" fractions were found to exhibit the highest cyclo-oxygenase activity, the [14C]-AA conversion rate in these incubates being twice as high as in the others. [14C]-labelled PGF2, PGE2 alpha and 6-keto-PGF1 alpha were found to be the principal PG products and there was no evidence of TxB2 formation in any of the incubates. [14C]-6-keto-PGF1 alpha was the main PG formed, constituting about 40% or more of the [14C]-PG activity in the incubates of all the fractions, whereas labelled PGE2 and PGF2 alpha were observed in considerably smaller and nearly equal amounts. The results demonstrate a considerable ability of human cardiac tissue to synthesize prostacyclin (PGI2) and, at the same time, the existence of local differences in tissue cyclo-oxygenase activity, which appears to be significantly higher in the endocardial layer than in the myocardium itself.