PLATELET-ACTIVATING-FACTOR AND HISTAMINE EFFECTS IN SYNOVIAL BLOOD-FLOW EVALUATED BY LASER-DOPPLER FLOWMETRY

Objective. To investigate platelet activating factor (PAF) and histamine effects in synovial circulation of rabbits. Methods. A laser-Doppler flowmeter was adapted to study the synovial blood flow. Either PAF or histamine were infused in the first femoral artery branch. The effects of PAF and histamine antagonists as well as of inhibitors of cycloxygenase products were evaluated. Results. PAF induced a vasoconstriction in synovial circulation, which was inhibited by the PAF antagonist, WEB 2170, a cycloxygenase inhibitor, indomethacin or a thromboxane synthesis inhibitor, dazmegrel. Histamine induced vasoconstriction in the synovial vessels. Promethazine not only inhibited this vasoconstriction but also induced a vasodilation, that was blocked by a combined treatment with promethazine and cimetidine. Pretreatment with WEB 2170 did not interfere with histamine effect, Conclusions. Our data indicate that PAF induces vasoconstriction in synovial blood flow through a receptor mediated mechanism and that thromboxane is involved in this effect. Histamine induces constriction or dilation in synovial vessels, through action on H-1 or H-2 receptors, respectively. This effect is not dependent on PAF.