Platelet serotonin changes in dogs with prosthetic aortic grafts

The purpose of this study was to elucidate the mechanisms underlying the striking reduction in platelet serotonin found after placement of prosthetic aortic grafts in dogs. Changes in platelet serotonin paralleled changes in platelet survival time. Both were reduced after graft placement, remained depressed for up to a year, and then returned to normal. In vivo release of serotonin was assessed by labeling autologous platelets with ⁵¹Cr (a nonreleasable, cytoplasmic label) and ¹⁴C-serotonin (a releasable, storage granule label). In dogs with grafts, ¹⁴C-serotonin persisted in the circulation beyond the life span of ⁵¹Cr-labeled platelets. The ratio of platelet ¹⁴C/⁵¹Cr activity over 5 days following infusion of double-labeled platelets markedly increased. These data indicated in vivo release and reutilization of labeled serotonin. In vitro platelet uptake of ¹⁴C-serotonin was assessed in separate experiments and was found to be depressed following graft placement. We conclude that the reduction in platelet serotonin stems from platelet interaction with aortic prostheses. Platelets adhere to the prosthetic surface, release serotonin, and recirculate. Reutilization of released serotonin occurs but may be limited by depressed platelet uptake. The net effect is a reduction in platelet serotonin. These findings support our view that platelet interaction with prosthetic surfaces is, in large measure, a reversible phenomenon, with platelets reentering the circulation in an altered state.