Effect of platelet-activating factor on microvascular permselectivity: dose-response relations and pathways of action in the hamster cheek pouch microcirculation.

Platelet-activating factor (PAF) has recently been described as a mediator of inflammatory processes. In this study, we quantitated the dose-response effects of topically applied PAF on microvascular permselectivity and investigated the biochemical pathways of this compound. Permselectivity alterations were assessed by measuring the clearance of macromolecules with fluorescein isothiocyanate dextran 150 (FITC-dx 150) as a tracer. The microvascular bed of the hamster cheek pouch served as a model. PAF was found to induce leakage of macromolecules from postcapillary venules. Control FITC-dx 150 plasma clearance (+/- SEM) was 72 +/- 10 nl/90 min. Clearances of 61 +/- 10 474 +/- 145, 622 +/- 57, 301 +/- 86, and 142 +/- 3 nl/90 min were obtained at PAF concentrations of 10(-9), 10(-8), 10(-7), 10(-6), and 10(-5) M, respectively. A one-way analysis of variance showed that the population means were not equal. Multiple comparison by the Student-Newman-Keuls test demonstrated that the clearances obtained with 10(-8), 10(-7), and 10(-6) M were significantly greater than controls. Significant differences existed between 10(-7) M PAF and 10(-9), 10(-6), and 10(-5) M PAF. In an effort to elucidate the biochemical pathways of PAF activity, several inhibitors of the arachidonic acid cascade and receptor blockers were used. Dexamethasone and kadsurenone attenuated the clearance response to PAF in a statistically significant manner, while indomethacin, OKY-046, and chlorpheniramine were without effect.(ABSTRACT TRUNCATED AT 250 WORDS)