KYNURENIC ACID AS AN ADDITIONAL ENDOGENOUS ANTI-AGGREGATORY FACTOR

Kynurenic acid (KNA) is an endogenous metabolite of tryptophan that has been characterized both in the brain and various peripheral organs that included blood vessels, kidneys, hearts, intestine and the eye. Its release from the vascular tissues which also release prostacyclin and nitric oxide directed us to investigate its influence on platelets aggregation. Exposure of guinea- pig platelets to KNA in concentrations ranging from 0.1 to 2mM inhibited adenosine diphosphate (ADP) and arachidonic acid (AA) induced aggregations in a dose-dependent manner.The inhibitory dose 50 values against ADP and AA were found to be 1.1±0.06 and 0.9±0.08 mM ,respectively. (N=8). The anti-aggregatory effect was significantly reversed in presence of exogenous Ca2+ . Elevation of the level of the plasma by 0.5mM Ca2+ reversed the anti- aggregatory effect KNA by 60±4.5 and 71.5±6.3% against ADP and AA, respectively (P 0.01 , N=8). It is suggested that KNA may be considered as an additional endogenous anti-aggregatory factor.