CORONARY VASOCONSTRICTOR AND VASODILATOR ACTIONS OF ARACHIDONIC ACID IN THE ISOLATED PERFUSED HEART OF THE RAT

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Abstract
1 The administration of arachidonic acid (AA) to the isolated perfused heart of the rat usually produced biphasic coronary responses characterized by initial vasoconstriction followed by prolonged vasodilatation. However, some responses were predominantly vasoconstrictor or vasodilator. 2 The non-steroidal anti-inflammatory agents (NSAA) indomethacin (1–5 mg/l) and naproxen (12.5–25 mg/l) reversibly inhibited both phases of the response induced by AA. 3 Pretreatment of animals with indomethacin (5 mg/kg) or naproxen (25 mg/kg) daily, resulted in unaltered coronary response to AA. Subsequent addition of NSAA to the perfusate produced inhibition of the AA effect. 4 Short infusions of acetylsalicylic acid at low concentrations (2.9 μg/ml), dipyridamole (0.6 μg/ml) and sulphinpyrazone (28.7 μg/ml) selectively inhibited the vasoconstrictor phase of the response to AA. 5 It was confirmed that metabolic coronary dilatation induced by cardiostimulation was inhibited by prolonged A A administration; this effect was prevented by NSAA pretreatment. Reactive hyperaemic responses to short lasting occlusions of coronary inflow were unaffected by NSAA. 6 Linolenic, linoleic, dihomo-γ-linolenic and oleic acid usually produced decreases in coronary flow which were unaffected by NSAA, dipyridamole or sulphinpyrazone. 7 Intra-aortic injections of AA, prostacyclin (PGI2) and prostaglandin E2 (PGE2) in the intact rat produced a dose-dependent decrease in blood pressure with the AA response inhibited by indomethacin. PGI2 and PGE2 produced long lasting coronary vasodilatation in the isolated heart. 8 The coronary actions of AA appear to be due to its transformation, within the easily accessible vascular wall, into prostaglandin and thromboxane-like substances. We suggest that a vasoconstrictor thromboxane A2-like substance may be responsible for coronary vasospasm. 9 Coronary insufficiency may also result from an inhibition of compensatory metabolic coronary dilatation by increased synthesis of PGE2 within the myocardial cell.