title: Platelet depletion and severity of streptococcal endocarditis.
abstract: OBJECTIVE
  To evaluate the importance of thrombocytopenia in streptococcal endocarditis using an animal model.
  
  
  METHODS
  A model of human septic endocarditis was established in rats (polyethylene catheters across the aortic valve and administration of Streptococcus sanguis, 5×10(7) colony forming units [cfu] intravenous). Thrombocytopenia at four levels was produced by antiplatelet serum. Secondary methods of producing thrombocytopenia were also evaluated. At sacrifice (96 h after platelet depletion and 72 h after infection), vegetations were removed, weighed, diluted, plated and counted. Potential mechanisms of the dose-response relationship between vegetation density and platelet count were evaluated.
  
  
  METHODS
  Controlled research laboratory experiments.
  
  
  METHODS
  Animal models of streptococcal endocarditis.
  
  
  RESULTS
  The bacterial density of the aortic valve vegetations significantly increased as the platelet count decreased (P=0.0007). In severely thrombocytopenic animals (two-dose antiplatelet serum), data suggest increased vegetation embolism. Platelet depletion, which was minimal with chemical methods, was produced most effectively by antithrombocyte serum. Platelet surfaces in endocarditis were found to express elevated CD62p proteins (72.7% endocarditis, 34.7% control). Platelet protein fractions were evaluated in vitro by both streptocidal (P=0.19) and phagocytosis-stimulating assays. Platelet presence in mature aortic valve vegetations averaged only about 2%.
  
  
  CONCLUSIONS
  In platelet depletion experiments using a rat model, a dose-response relationship of peripheral circulating platelet depletion to aortic valve vegetation density was found. The mechanism relating thrombocytopenia to endocarditis severity remains unresolved.
authors.affiliation: Section of Infectious Diseases, School of Medicine, University of Missouri-Kansas City, Kansas City, Missouri.
authors.forename: L
authors.initials: L
authors.lastname: Dall
authors.forename: T
authors.initials: T
authors.lastname: Miller
authors.forename: B
authors.initials: B
authors.lastname: Herndon
authors.forename: I
authors.initials: I
authors.lastname: Diez
authors.forename: M
authors.initials: M
authors.lastname: Dew