phosphodiesterase

Ro 15-2041 inhibits platelet aggregation induced by all common platelet agonists in platelet-rich plasma obtained from various species including man (IC ₅₀ =1-3 μM). Ro 15-2041 potentiates platelet inhibition by prostacyclin, the prostacyclin-induced increase of intraplatelet cyclic (c) AMP levels and inhibits the collagen-induced release of serotonin and beta-thromboglobulin. Ro 15-2041 reduces the increase and accelerated the normalization of cytosolic free Ca ²⁺ in thrombin-stimulated human platelets. Ro 15-2041 is a potent (IC ₅₀ =70 nM) and selective inhibitor of platelet cAMP-phosphodiesterase activity. Whereas Ro 15-2041 causes complete inhibition of cAMP-phosphodiesterase activity in human platelet supernatants, breakdown of cAMP in cardiac homogenates is depressed to maximally 50%. In human brain and rabbit uterus Ro 15-2041 is at least 1000 times less potent. By comparison, papaverine fully inhibits phosphodiesterase activity in all four tissues with similar IC ₅₀ values of about 5 μM. Furthermore, Ro 15-2041 selectively inhibits cAMP-phosphodiesterase activity of a bovine calmodulin-independent but not of a calmodulin-dependent enzyme preparation.