CYCLIC-AMP AND CYCLIC-GMP PHOSPHODIESTERASE INHIBITION BY AN ANTIPLATELET AGENT, -[(3-METHYLENE-2-OXO-5-PHENYL-5-TETRAHYDROFURANYL) METHOXY]QUINOLINONE (CCT-62)

The antiplatelet activity of -[(3-methylene-2-oxo-5-phenyl-5-tetrahydr ofuranyl) methoxy]quinolinone) (CCT-62) was determined in vitro in rab bit platelets. CCT-62 inhibited rabbit platelet aggregation and ATP re lease caused by thrombin (0.1 U/ml), platelet-activating factor (2 ng/ ml), collagen (10 mu g/ml), arachidonic acid (100 mu M), and 9,11-dide oxy-9 alpha, 11 alpha-methanoepoxy prostaglandin F-2 alpha (1 mu M) in a concentration-dependent manner. The TC50 values for platelet aggreg ation were 18.4 +/- 4.5, 10.1 +/- 1.6, 3.0 +/- 0.9, 1.5 +/- 0.3 and 1. 0 +/- 0.3 mu M, respectively. In addition, CCT-62 disaggregated the cl umped platelets caused by these aggregation inducers. It also inhibite d phosphoinositide breakdown and intracellular calcium elevation induc ed by the above platelet aggregation inducers. CCT-62 increased intrac ellular cyclic AMP and cyclic GMP levels in a concentration- and time- dependent manner. Furthermore, it potentiated cyclic AMP formation cau sed by prostaglandin E, but not that caused by 3-isobutyl-1-methylxant hine. CCT-62 did not affect adenylate or guanylate cyclase but inhibit ed cyclic AMP- and cyclic GMP-phosphodiesterase activities. The antipl atelet effect of CCT-62 was reversed by a protein kinase A inhibitor, N-[2-( romocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89). This data clearly indicated that CCT-62 is an inhibitor of phosphodiesteras es and that its antiplatelet effect is mainly mediated by elevation of cyclic AMP levels. (C) 1998 Elsevier Science B.V. All rights reserved .