The interaction of platelets with aortic subendothelium: inhibition of adhesion and secretion by prostaglandin I2

We have studied the effect of prostaglandin I2 on platelet turnover, attachment to the subendothelium, and secretion following balloon deendothelialization of the rabbit aorta. Survival of 51Cr-labeled platelets in the balloon-injured animals remained normal. Thirty minutes after injury, there were 4.52 X 10(6) platelets/sq cm attached to the aortic surface, which was 87% covered by platelets. Although plasma platelet factor 4, as measured by radioimmunoassay, did not rise above the normal level of 6.8 +/- 2.6 ng/ml (mean +/- SEM) during the first hour after balloon injury, platelet factor 4 antigen was detected within the vessel wall by direct immunofluorescence within 30 min of injury. An infusion of 650–850 ng/kg/min prostaglandin I2 completely inhibited platelet aggregation and reduced surface coverage by 84% and platelet attachment by 63%. Animals given 50–100 ng/kg/min prostaglandin I2, which only partially inhibited platelet aggregation, had 70% of the aortic surface covered by platelets. Platelet factor 4 antigen was also detected within the aortic wall. Platelet attachment was normal in animals that had been given 850 ng/kg/min prostaglandin I2 prior to balloon injury but sacrificed after the infusion was stopped and ex vivo platelet aggregation had returned to normal.