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Metabolically active coronary microvessels (generally less than 100 micrometers in diameter) were isolated from bovine hearts. These preparations were virtually free of contaminating myocytes and consisted of a mixture of arterioles, venules, capillaries, and collagen fibers. The prostaglandin biosynthetic capacity of isolated coronary microvessels was assessed by quantitating conversion of 14C-arachidonic acid and 14C-prostaglandin endoperoxide (PGH2) to prostaglandins. Coronary microvessels were found to exhibit low cyclooxygenase activity, i.e., minimal conversion (less than 1%) of arachidonic acid (AA) to prostaglandins when compared with either the coronary artery (3.6% conversion of AA) or coronary vein (3.3%). Isolated myofibril fractions demonstrated virtually no cyclooxygenase activity (less than 0.1%). Two enzymatic endoperoxide metabolizing activities were evident in the microvessels, prostacyclin synthetase and PGE isomerase. When compared on a microsomal protein basis, the coronary artery exhibited higher prostacyclin synthetase activity than the microvessels but was devoid of PGE isomerase activity. In contrast, whereas PGE isomerase activity was detectable in the coronary vein, the activity was lower than that of the microvessels; further, it could not be demonstrated in the other myocardial fractions. A glutathione-enhanced PGD-forming activity was present in high speed supernatants derived from the coronary artery and vein preparations, but was not present in the coronary microvessel or isolated myofibril fractions. From these studies we conclude that (1) the major source of prostaglandins released into the coronary circulation is the coronary vasculature, and (2) the resistance elements of the coronary circulation differ from the larger elements (i.e., arteries and veins) in the enzymes of the prostaglandin biosynthetic pathway present and thus in the nature and perhaps quantity of prostaglandins biosynthesized.

Sites of prostaglandin synthesis in the bovine heart and isolated bovine coronary microvessels.