Influence of platelet-activating factor on cerebral microcirculation in rats: part 1. Systemic application.

Background And Purpose: Platelet-activating factor (PAF) has been demonstrated to have a mediator function in shock, with some of its deleterious effects being attributed to its influence on microcirculation. Systemic PAF concentrations as found in shock could also compromise the cerebral microcirculation. Our purpose in the present study was to examine the influence of systemically applied PAF on microvascular perfusion and leukocyte-endothelium interactions in cerebral microvessels.

Methods: A closed cranial window technique was used for intravital fluorescence microscopy of the brain surface. PAF was infused in concentrations of 10(-12), 10(-9), and 10(-6) mol/L into the carotid artery (5 mL/h for 20 min) of Sprague-Dawley rats (n=30). The selective PAF receptor antagonist WEB 2170BS (2 mg/kg body weight) was used to inhibit specific PAF effects.

Results: The number of leukocytes (cells/100 microm. min) rolling along or adhering at the venular endothelium increased following infusion of PAF 10(-6) mol/L from 7.7+/-2.5 to 24.4+/-8.9 (P<0.05) and from 1.9+/-0.5 to 6.9+/-2.2 (P<0.05), respectively, within 2 hours. Mean arterial pressure decreased from 92+/-22 mm Hg to 49+/-17 mm Hg (P<0.05). The lower concentrations of PAF were less effective to decrease mean arterial pressure but also induced leukocyte-endothelium interactions. The intravenous administration of WEB 2170BS 15 min before the infusion of PAF 10(-6) mol/L prevented both systemic hypotension and activation of leukocyte-endothelium interactions.

Conclusions: Increased systemic blood levels of PAF as found during shock can not only cause systemic arterial hypotension but also induce leukocyte-endothelium interactions in cerebral venules. The activation of leukocytes was found to be independent of PAF-induced arterial hypotension. The specificity of these results is confirmed by the findings that WEB 2170BS could inhibit the PAF-induced systemic hypotension as well as the activation of leukocytes.