Prostacyclin biosynthesis and phospholipase activity in hypoxic rat myocardium

Phospholipid metabolism was studied in rat myocardial slices that were incubated under normoxia or hypoxia for up to 24 hours. Phospholipid degradation was prominent in hypoxic myocardium, particularly phosphatidylcholine, which markedly decreased after 24 hours of hypoxia. In contrast, lysophosphatidylcholine increased. The mechanism of phospholipid degradation in hypoxic myocardium was studied. The highest activity for phospholipase A2 among subcellular fractions was found in microsomal fraction. In hypoxic myocardium, this phospholipase A2 activity markedly increased and had substrate specificity toward phosphatidylcholine and phosphatidylethanolamine. Phosphatidylcholine was slightly hydrolyzed in control myocardium, but it was markedly hydrolyzed in hypoxic myocardium. Phospholipase C activity was found in cytosol and had a high substrate specificity toward phosphatidylinositol. In hypoxic myocardium, its activity gradually decreased during hypoxic incubation. Prostacyclin biosynthesis was also determined. The synthesis of prostacyclin in hypoxic myocardial microsomes did not increase. These results suggest that hypoxia causes phospholipid degradation and activates phospholipase A2 activity.