Exogenous prostacyclin decreases vasoconstriction but not platelet thrombus deposition after arterial injury

Abstract Objectives . The aim of this study was to examine the in vivo effects of increasing doses of prostacyclin (PGI 2 ) on arterial vasoconstriction, platelet deposition and their interrelation after balloon injury of porcine carotid arteries. Background . Extensive platelet deposition and localized vasoconstriction occur acutely after arterial injury in vivo. The platelet deposition and vasoconstriction are directly correlated, and previous studies suggest that platelets may mediate the vasoconstrictive response. However, it is unclear whether vasoconstriction contributes to platelet deposition. Methods . Seven pigs received an intravenous infusion of PGI 2 at 10 ng/kg per min (PGI 2 10), 8 pigs at 50 ng/kg per min (PGI 2 50) and 4 pigs at 500 ng/kg per min (PGI 2 500); 24 pigs with saline infusion served as a control group. Results . Vasoconstriction immediately proximal and distal to the balloon-dilated carotid arterial segment where selective endothelial injury occurred was directly related to indium-111-labeled platelet deposition within the dilated segment in both control pigs and PGI 2 -treated pigs. However, this relation was such that for any given level of platelet deposition relative to control, PGI 2 decreased vasoconstriction in a dose-related manner. None of the treatments (PGI 2 10, 50 or 500) decreased quantitative 111 Inlabeled platelet deposition or the proportion of deeply injured arteries with mural thrombus (91%, 70% or 75%, respectively, p = NS) compared with values in control pigs (81%). Thus, vasoconstriction was directly related to platelet deposition in control and PGI 2 -treated animals, but vasodilation alone did not decrease platelet deposition. Conclusions . Intravenous infusion of PGI 2 significantly decreases vasoconstriction but not platelet deposition or mural thrombosis after arterial injury by balloon dilation. It is therefore unlikely that vasoconstriction mediates platelet deposition in this model. At hemodynamically tolerated doses, PGI 2 infusion probably will not prevent the thrombotic complications associated with angioplasty.