The tachyphylactic effect of arachidonic acid on in-vivo ADP induced arterial platelet thrombosis

The continuous superfusion of arachidonic acid over a branch of the mesenteric artery in an animal in-vivo model results in an initial increase followed by a decrease to control values of ADP induced platelet thrombogenesis. This phenomenon is observed in normal rats as well as in rats submitted to the intravenous administration of ASA three hours prior to the investigation. In the latter group the cyclooxygenase of the platelets is permanently affected while the cyclooxygenase of the endothelial cells is regenerated at the time the investigation is started. The tachyphylactic-like phenomenon observed with arachidonic acid is probably related to the dynamics of the enzymatic reactions of the arachidonate cascade involving the platelets and the endothelial cells surrounding the local de-endothelialized area.