EFFECT OF 1-(3-CHLOROANILINO)-4-PHENYLPHTHALAZINE (MY-5445), A SPECIFIC INHIBITOR OF CYCLIC-GMP PHOSPHODIESTERASE, ON HUMAN-PLATELET AGGREGATION

  • 1 January 1984
    • journal article
    • research article
    • Vol. 228  (2) , 467-471
Abstract
The effects of a novel compound, 1-(3-chloroanilino)-4-phenylphthalazine (MY-5445), on cyclic nucleotide metabolism and in vitro aggregation of human platelets were investigated. The concentrations of MY-5445 producing 50% inhibition of human platelet aggregation induced by 3 .mu.M ADP, 3 .mu.g/ml of collagen and 100 .mu.g/ml of arachidonic acid were 0.07, 0.02 and 0.17 .mu.M, respectively. Addition of MY-5445 significantly elevated cGMP content in human platelets but had no effect on cAMP content, suggesting that the drug affects principally the cGMP metabolism in the platelet. Although My-5445 had no effect on either adenylate cyclase of guanylate cyclase activity, it inhibited specifically human platelet cGMP phosphodiesterase which was separated from cAMP phosphodiesterase by diethylaminoethyl-cellulose column chromatography. The inhibitory effect of MY-5445 on cGMP phosphodiesterase was also demonstrated by direct binding of the enzyme to MY-5445 coupled Sepharase, which was a useful tool for purifying the cGMP phosphodiesterse from human platelet. MY5445 apparently inhibits human platelet aggregation by increasing cGMP content and it provides a useful probe for elucidating the role of cGMP in platelet aggregation.