Platelet accumulation and turnover on de-endothelialized aortae in rats

Previous studies indicate that the subendothelium of rabbit aortae de-endothelialized with a balloon catheter rapidly becomes covered with a monolayer of platelets; after 60 min few additional platelets accumulate and although most platelets are lost from the injured surface by 4 days, there is a substantial delay before re-endothelialization. We examined the dynamics of platelet accumulation on rat aortae de-endothelialized with a balloon catheter to determine if the response to this type of injury is similar to rabbit aortae. When 51Cr-platelets were injected prior to aortic de-endothelialization, 25,500 +/- 2,750 platelets/mm2 accumulated on rat subendothelium in the first 15 min. After 60 and 92 h, fewer platelets remained on the surface (13,740 +/- 2,400 and 5,020 +/- 1,330 platelets/mm2, respectively). When 51Cr-platelets were injected into rats 30 min after injury, platelet accumulation in a 30-min period was 8,610 +/- 1,230 platelets/mm2. By 4 days rat aortae did not accumulate newly injected platelets significantly in a 30-min period, but in a 24-h period 20,600 +/- 3,490 platelets/mm2 accumulated. Morphologically, the non-endothelialized areas of rat aortae were almost completely covered with platelets 4 days after injury. Fourteen days after injury, rat aortae did not accumulate newly injected platelets and, morphologically, no platelets were present on the surface which was almost re-endothelialized. Thus, in rats, as with rabbits, platelets rapidly accumulate on de-endothelialized aortae and the ability to attract newly introduced platelets is considerably reduced shortly after injury. In contrast to rabbits, however, de-endothelialized aortae in rats remain attractive to new platelets up to 4 days following injury, but less so than at the time of injury. Also, in contrast to rabbits, 14 days after injury to rat aortae the surface is almost completely re-endothelialized. Thus, there are species differences in platelet interactions with de-endothelialized vessels.