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

Objective. To investigate platelet activating factor (PAF) and histami ne effects in synovial circulation of rabbits. Methods. A laser-Dopple r flowmeter was adapted to study the synovial blood flow. Either PAF o r histamine were infused in the first femoral artery branch. The effec ts of PAF and histamine antagonists as well as of inhibitors of cyclox ygenase products were evaluated. Results. PAF induced a vasoconstricti on in synovial circulation, which was inhibited by the PAF antagonist, WEB 2170, a cycloxygenase inhibitor, indomethacin or a thromboxane sy nthesis inhibitor, dazmegrel. Histamine induced vasoconstriction in th e synovial vessels. Promethazine not only inhibited this vasoconstrict ion but also induced a vasodilation, that was blocked by a combined tr eatment with promethazine and cimetidine. Pretreatment with WEB 2170 d id not interfere with histamine effect, Conclusions. Our data indicate that PAF induces vasoconstriction in synovial blood flow through a re ceptor mediated mechanism and that thromboxane is involved in this eff ect. Histamine induces constriction or dilation in synovial vessels, t hrough action on H-1 or H-2 receptors, respectively. This effect is no t dependent on PAF.