Studies on antiplatelet effects of OP-41483, a prostaglandin l2 analog, in experimental animals II. Mechanism of its antiplatelet effect.

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概要

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• The mechanism for the inhibition of platelet functions by a prostaglandin I2 analog, OP-41483, was studied with guinea pig platelets. OP-41483, and PGI<SUB>2</SUB> as well, inhibited aggregation, ADP release and thromboxane formation of platelets with IC50 values of 4.3-5.8 ng/ml and 0.6-0.9 ng/ml, respectively. The ligand binding study using [<SUP>3</SUP>H]-OP-41 483 suggested that OP-41 483 bound with different affinities to two classes of bindig sites on platelets. The dissociation constant of OP-41483 for the higher affinity site corresponded to the IC50 values of its antiplatelet effect. PGI<SUB>2</SUB> as well as OP-41483 displaced [<SUP>3</SUP>H]-OP-41483 previously bound to platelets, thus indicating that both agents exerted their antiplatelet effects by binding to the same site on platelets. OP-41483 and PGI<SUB>2</SUB> activated adenylate cyclase and raised cyclic AMP levels in platelets. However, their inhibitory effect on platelet aggregation was not fully antagonized by an adenylate cyclase inhibitor, 2', 5'-dideoxyadenosine (DDA), at a concentration completely inhibiting the increase of cyclic AMP. Moreover, this DDA-resistant effect of OP-41483 disappeared in the presence of calcium chloride (10<SUP>-4</SUP>-10<SUP>-3</SUP> M). OP-41483 and PGI<SUB>2</SUB> inhibited thrombin-induced Ca<SUP>++</SUP> influx into platelets. The inhibition of Ca<SUP>++</SUP> influx was not reversed by DDA. Based on these results, we speculate that the inhibitory effects of OP-41483 and PGI<SUB>2</SUB> on platelet functions are produced through dual mechanisms: one mediated by activation of adenylate cyclase and the other by an inhibition of Ca<SUP>++</SUP> influx; and these two mechanisms seem to be independent of each other.

• 公益社団法人 日本薬理学会の論文

著者

• Fujitani Buichi

  Research Laboratories Dainippon Pharmaceutical Co. Ltd.

• WAKITANI Korekiyo

  Research Institute, Ono Pharmaceutical Co., Ltd.

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