Uptake, stimulated release and metabolism of (1-14C)-eicosapentaenoic acid in a perfused organ of the rabbit.

The isolated rabbit ear was prelabeled by perfusion with (1-14C)-eicosapentaenoic acid (EPA). Uptake and distribution in lipids, basal release and, in particular, stimulated release and metabolism was studied. In a series of experiments a comparison with results obtained by labeling the perfused organ with (1-14C)-arachidonic acid (AA) was made. Approximately 80% of the perfused labeled EPA was incorporated into the tissue. The main peak (74% of the incorporated radioactivity) was found in the phospholipids. Following incorporation of labeled EPA, basal release of EPA but ot of trienoic prostaglandins (PGs) could be observed. Bolus injection of bradykinin (3 micrograms) and the calcium-ionophore A23187 (10 micrograms) led to an immediate increased release of radioactivity in the effluent which declined within 10--20 min. Analysis of the extracted effluent by thin layer chromatography (TLC) showed that only the release of EPA and of radioactivity at the Rf-value of 12-L-hydroxy-5,8,10,14-eicosatetraenoic acid (HETE) was increased following stimulation by bradykinin and A23187. No labeled trienoic PGs could be detected. Upon injection of A23187 in the presence of indomethacin (3 micrograms/ml) there was no reduction of any peak of radioactivity on the TLC-plate, indicating that no cyclooxygenase product of EPA was generated. The extremely high dose of 10 micrograms bradykinin or 50 micrograms A23187 led to a small release of labeled PGI3 (A23187) and to a somewhat higher release of labeled PGE3 (bradykinin, A23187). In some experiments release and metabolism of labeled EPA were compared with those of labeled AA.(ABSTRACT TRUNCATED AT 250 WORDS)