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 cyclooxygenase products were evaluated.


RESULTS
PAF induced a vasoconstriction in synovial circulation, which was inhibited by the PAF antagonist, WEB 2170, a cyclooxygenase 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 H1 or H2 receptors, respectively. This effect is not dependent on PAF.
Rocha
F A
FA
Department of Medicine, University of São Paulo, Brazil.
Jancar
S
S
Fraga
C A
CA
Timo-Iaria
C
C
De Brum-Fernandes
A J
AJ
D000818:Animals; D001381:Azepines / Q000494:pharmacology; D005260:Female; D006632:Histamine / Q000494:pharmacology*; D017078:Laser-Doppler Flowmetry; D008297:Male; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011817:Rabbits; D012039:Regional Blood Flow / Q000187:drug effects; D013583:Synovial Membrane / Q000098:blood supply*; D014230:Triazoles / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects
D001381:Azepines; D010972:Platelet Activating Factor; D014230:Triazoles; D006632:Histamine; C063964:bepafant