Endothelium‐dependent vasodilator effects of platelet activating factor on rat resistance vessels

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Abstract
1 To elucidate the mechanisms of the powerful and long-lasting hypotension produced by platelet activating factor (PAF), its effects on perfusion pressure in the perfused mesenteric arterial bed of the rat were examined. 2 Infusion of PAF (10−11 to 3 × 10−10m; EC50 = 4.0 × 10−11m; 95%CL = 1.6 × 10−11–9.4 × 10−11m) and acetylcholine (ACh) (10−10 to 10−6m; EC50 = 3.0 ± 0.1 × 10−9m) produced marked concentration-dependent vasodilatations which were significantly inhibited by treatment with detergents (0.1% Triton X-100 for 30s or 0.3% CHAPS for 90s). 3 Pretreatment with CV-6209, a PAF antagonist, inhibited PAF- but not ACh-induced vasodilatation. 4 Treatment with indomethacin (106m) had no effect on PAF- or ACh-induced vasodilatation. 5 These results demonstrate that extremely low concentrations of PAF produce vasodilatation of resistance vessels through the release of endothelium-derived relaxing factor (EDRF). This may account for the strong hypotension produced by PAF in vivo.