Platelet antiaggregatory substances inhibit arachidonic acid induced coronary constriction

Isolated perfused hearts of rats and guinea pigs reacted to arachidonic acid (AA) with coronary vasoconstriction followed by vasodilatation. The infusion of prostacyclin (PGI2), Iloprost, hydralazine (HYD), and nifedipine (NFP) elicited a vasodilatation that nullified the coronary flow reserve, therefore the AA-induced vasodilatation was abolished. Dipyridamole (DPY) and 1-methyl-3-isobutylxanthine (MIX) produced a slight coronary dilatation without restricting the dilatation induced by AA. Regardless of their vasodilator action, all these drugs acted by inhibiting the AA-induced coronary constriction, while their infusion lasted. We postulated that a thromboxane-like substance, formed from AA in the vascular walls, would be responsible for the coronary vasoconstriction caused by AA. The inhibition of the AA-induced coronary constriction by PGI2, Iloprost, HYD, NFP, DPY, and MIX may be explained by an inhibitory action of these drugs on the synthetic processes of the thromboxane-like substance.