Comparison of anti-aggregatory effects of PGI(2), PGI(3) and iloprost on human and rabbit platelets

In human, prostaglandin I-3 (PGI(3)) is as potent inhibitor of platelet agg regation as prostacyclin (PGI(2)). However the data on the anti-aggregatior y effect of this prostaglandin is scanty on human and is absent on platelet s of other species. The potency of PGI(3) on other species may be different if there are differences in the structure of receptors. Comparison of the rank orders of the potency of the selective agonists in different species m ay provide evidence for the existence of such differences. The aim of this work was to study the anti-aggregatory effect of PGI(3) on the platelets of human and rabbit and compare the rank orders of the potency of PGI(2), PGI (3), and iloprost, a synthetic analogue of PGI(2), on the platelets of the two species. Experiments were performed in the suspensions of washed platel ets prepared from the blood anticoagulated with trisodium citrate solution. A prostaglandin concentration causing 50% inhibition of ADP-induced platel et aggregation (IC50) was obtained from concentration-effect curves. On hum an platelets, PGI(2), was as effective as PGI(2), while on rabbit platelets , the value of IC50 for PGI(3) (10.2+/-1.6 nM) was twofold higher than that of PGI(2). The rank orders of agonist potency are different in rabbit comp ared to those of human. This indicates that the prostacyclin receptors of r abbit platelets are pharmacologically different from those of human. Copyri ght (C) 2001 S. Karger AG, Basel.