title: Specific binding of the new stable epoprostenol analogue beraprost sodium to prostacyclin receptors on human and rat platelets.
abstract: Binding of beraprost sodium (sodium dl-4-[(1R,2R,3aS,8bS)-1,2,3a,8b-tetrahydro-2-hydroxy-1-[(3S, 4RS)- 3-hydroxy-4-methyl-oct-6-yne-(E)-1-enyl] -5- cyclopenta[b]benzofuranyl]butyrate, TRK-100), a new potent antithrombotic agent, to washed platelets of humans and rats was studied. [11-3H]-TRK-100 binding was rapid, reversible, saturable, and highly specific. Scatchard analysis of concentration-dependent binding to human platelets revealed a single class of specific binding sites with an equilibrium dissociation constant (Kd) of 133 nmol/l and a maximal concentration of binding sites (Bmax) of 46 fmol/10(8) platelets (275 sites/cell). Similar binding was observed on rat platelets. The Kd and Bmax were 66 nmol/l and 124 fmol/10(8) platelets (750 sites/cell), respectively. Competitive studies indicated that TRK-100 was 1.5 times less active than prostacyclin (epoprostenol, PGI2), but was 3 times more potent than PGE1 in displacing [3H]-TRK-100 from the binding sites on rat platelets. PGE2, PGD2, PGF2 alpha, and pinane thromboxane A2, a stable thromboxane A2 analogoue, had no affinity for the binding sites. The relative affinity of the four enantiomers of TRK-100--APS-314d, 315d, 3141 and 3151--for the binding sites was 100: 14: less than 1: less than 1, respectively. These results suggest that TRK-100 is a useful tool for studying biological roles of PGI2 as well as for use as an antithrombotic agent since TRK-100 mimics its actions via specific interaction with PGI2 receptors.
authors.affiliation: Central Research Laboratories, Kaken Pharmaceutical Co., Ltd., Kyoto, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Kajikawa
authors.forename: K
authors.initials: K
authors.lastname: Nogimori
authors.forename: T
authors.initials: T
authors.lastname: Murata
authors.forename: S
authors.initials: S
authors.lastname: Nishio
authors.forename: S
authors.initials: S
authors.lastname: Uchiyama
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D011464:Epoprostenol / Q000097:blood* / Q000031:analogs & derivatives; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D010975:Platelet Aggregation Inhibitors / Q000097:blood*; D051381:Rats; D011919:Rats, Inbred Strains; D044006:Receptors, Epoprostenol; D011982:Receptors, Prostaglandin / Q000378:metabolism*; D013696:Temperature
chemical_list: D010975:Platelet Aggregation Inhibitors; D044006:Receptors, Epoprostenol; D011982:Receptors, Prostaglandin; C048081:beraprost; D011464:Epoprostenol