The role of plasma proteins and stress in the assessment of hemocompatibility

The physiological and psychological conditions of subjects supplying blood for hemocompatibility tests significantly affect the behavior of platelets in terms of both adhesion and activation. The responses of platelets to a s tandard biomaterial, polyethylene (PE), were examined with blood collected from male rabbits both in basal conditions and after stress, Different medi a were utilized. First, platelet-rich plasma (PRP) was used to obtain a PE response to contact with platelets. Then platelets drawn from PRP were isol ated and washed with Krebs-Ringer solution. One aliquot was suspended in se rum (Pw-S) where fibrinogen was absent, another aliquot in Krebs-Ringer sol ution (Pw-KR) tin order to avoid the influence of the plasma proteins on pl atelets), and a third aliquot in the original plasma from which the platele ts were drawn (Pw-PPP) tin order to restore the initial condition of the pl asma but with washed platelets). The analysis of platelet adhesion and morp hology was performed by Scanning Electron Microscopy (SEM). Differences in platelet adhesion and morphology were observed with four different media in nonstressed animals, with Pw-PPP showing a higher number and Pw-S and PW-K R lower numbers. Platelet morphology indicated low levels of activation. Th e platelets drawn from stressed subjects could not be counted in either PRP or PPP medium because they were fully aggregated and adhered; in contrast, in Pw-KR and Pw-S, no significant differences were found with respect to n onstressed conditions, and there was little difference in platelet morpholo gy. All of these factors underline the role of plasma proteins, in particul ar fibrinogen, in the stress-induced activation of platelets. (C) 1999 John Wiley & Sons, Inc.