Non-platelet-mediated vascular actions of 1-O-alkyl-2-acetyl-sn-3-glyceryl phosphorycholine (a synthetic PAF).

Rat platelets fully responsive to thrombin and collagen did not release 3H-serotonin with up to 10 microgram/ml synthetic PAF. Therefore, an experimental approach using 57Co and 113Sn radiolabelled microspheres was developed to evaluate the effect of PAF on cardiac output (CO), peripheral vascular resistance (PVR) and redistribution of CO among organs. The effect on vascular permeability was studied by measuring the clearance of 125I-HSA and the variations of the haematocrit. A significant fall in blood pressure and PVR was found with doses of PAF from 50 to 5000 ng. Moreover, the highest doses of PAF induced also a marked reduction in blood volume. A significant fall in spleen, coronary and kidney output was found but not in CO. Our data show that PAF, by itself, induces a fall in PVR and at higher doses also in circulating volume, both accounting for the hypotensive effect. The redistribution of CO seems to be the expression of a non-uniform action upon PVR.