INTERACTION BETWEEN THE EFFECTS OF 5-HYDROXYTRYPTAMINE AND ADRENALINEON THE GROWTH OF PLATELET THROMBI IN THE CORONARY-ARTERY OF THE ANESTHETIZED DOG

1 The interaction between adrenaline and 5-hydroxytryptamine (5-HT) ha s been quantitated on the rate of thrombus formation, in the stenosed coronary artery with damaged endothelium of the anaesthetized dog. 2 C hanges in the plasma concentration of adrenaline were produced by vary ing the rate of an intravenous infusion of adrenaline and in the effec ts of 5-HT, by intravenous injections of the selective 5-HT2 receptor antagonist, ICI 170809. 3 Increases in the plasma concentration of adr enaline, which did not cause significant changes in blood pressure and heart rate, increased the rate of thrombus formation. 4 Antagonism of the 5-HT2 receptor by ICI 170809, in the absence of an infusion of ad renaline, abolished thrombus formation (mean ED50 0.41 mug kg-1, i.v.) .5 The effects of adrenaline were non-competively antagonized by ICI 1 70809; maximum effects were obtained in the dose-range 50-200 mug kg-1 , i.v., when the mean dose-ratio increase in adrenaline required to re store equivalent rates of thrombus formation was 39 fold. 6 These resu lts are consistent with a synergism between adrenaline and 5-HT and em phasize the importance of both on thrombus formation.