REGIONAL HEMODYNAMIC-EFFECTS OF PLATELET-ACTIVATING-FACTOR IN THE RAT

The effects of platelet activating factor (PAF) on haemodynamics in th e absence and presence of the potent PAF receptor antagonist TCV-309 y l]carbonamoyl]ethyl]carbamoyl]-1-propylpyridinium nitrate) were studie d by the microsphere technique in pentobarbitone-anaesthetized rats. I .v. infusion of the low dose PAF (0.05 mu g kg(-1) min(-1)) did not si gnificantly alter mean arterial pressure, cardiac output or total peri pheral resistance but increased arterial conductances in the stomach, intestine, caecum and colon and reduced conductance in the spleen. I.v . infusion of the high dose of PAF (0.3 mu g kg(-1) min(-1)) markedly reduced mean arterial pressure (-53 mm Hg) and cardiac output (-62%) a nd insignificantly increased total peripheral resistance. Arterial con ductances in the lungs, stomach, intestine, caecum and colon, kidneys and spleen were reduced and those in the heart and muscle were increas ed. TCV-309 (10 mu g kg(-1)) abolished all changes in arterial pressur e, cardiac output and total peripheral resistance and arterial conduct ances elicited by either the low or the high dose of PAF. The results show that a non-hypotensive dose of PAF caused vasodilatation of the g astrointestinal organs and vasoconstriction of the spleen. A high dose of PAF which markedly decreased arterial pressure and cardiac output caused vasodilatation of the heart and muscle and vasoconstriction of the lungs (bronchial), gastrointestinal organs, kidneys and spleen. Al l haemodynamic changes were blocked by TCV-309 indicating the involvem ent of PAF receptors.