Summary
The ability of synthetic platelet-activating factor (PAF) given intravenously to produce
loss (extravasation) of protein rich plasma (resulting in hemoconcentration) has been
examined using guinea pigs. Hemoconcentration induced by PAF was not prevented by
prior administration of inhibitors of thromboxane synthetase (7-(3-pyridyl)heptanoic
acid, UK-37,248-01), PGI2, aspirin, indomethacin or antiserum induced thrombocytopenia. Calcium channel blockers
(nifedipine, verapamil, diethyl-amino octyltrimethoxybenzoate, diltiazem), antihistamines
(pyrilamine, cimetidine, diphenhydramine), or the elevator of cAMP IBMX were ineffective
in blocking PAF-induced hemoconcentration. In contrast, CV-3988, reported to be a
specific antagonist to PAF, was 98% inhibitory of PAF extravasation when given i.
a. at 3.5 mg/kg. The ED50 was 0.14 mg/kg I. A. and 15 mg/kg p.o. against 75 ng/kg PAF. These data suggest that
PAF-induced hemoconcentration involves receptor mediated alterations of vascular permeability
that are inhibited by a specific PAF antagonist.
Keywords
Platelet-activating factor - Guinea pig - Extravasation - Endothelial permeability
- Thromboxane inhibitors - Calcium channel blockers - Antihistamines