The DP-receptor Dependence of the Inhibitory Effects of PGD, on Collagen-induced Platelet Aggregation and TXA, Synthesis in Human Whole Blood in Vitro

Abstract

The DP receptor-dependence of inhibition of platelet aggregation (PA), degranulation, and TXA(2) synthesis, by PGD(2), in human whole blood, has not been established since selective antagonists have only recently been developed. Accordingly, the effects of PGD(2) (30 nM), were determined using the DP receptor antagonists AH6809 (50 µM) and 868C84 (0.5 µM), and results were compared with those obtained using the stable and DP receptor-specific agonist 572C85 (30 nM). With collagen at 0.3 µg/ml, PGD(2) markedly inhibited PA (6 vs 91% PA, p >0.03, n = 12) and both AH6809 and 868C84 alone also inhibited PA but less markedly (62 and 63% PA, respectively) and both antagonists largely prevented the antiaggregatory action of PGD(2) (57 and 52% PA, respectively). PGD(2) also markedly inhibited TXB(2), formation (reflecting inhibition of TXA(2) synthesis) (19 vs 48 nM TXB(2), p>0.03). AH6809 and 868C84 alone had little effect (both 45 nM) but both antagonists significantly reduced the inhibitory effect of PGD(2) on TXB(2) formation (35 and 33 nM, respectively, p> 0.03 vs PGD(2) alone). PGD(2) also inhibited β-thromboglobulin release, but only to a similar extent as with AH6809 and 868C84 alone. With collagen at 3.0 μg/ml, PGD(2) again inhibited PA (60 vs 96% PA, p >0.03), AH6809 and 868C84 alone had no effect on PA (98 and 96% respectively) but effectively abolished the antiaggregatory effect of PGD(2). PGD(2) also inhibited TXB(2) formation (194 vs 339 nM, p > 0.03) and this effect of PGD(2) was effectively abolished both by AH6809 and 868C84 (313 and 308 nM, respectively). Results obtained with 572C85 largely confirmed those obtained with PGD(2), and with collagen at 0.3 µg/ml, 868C84 effectively abolished inhibition of both PA and TXB(2) formation by 572C85. Thus, DP receptor-dependent inhibition of both aggregation and TXA(2) synthesis both by PGD(2) and the more selective DP receptor agonist 572C85, was established using the DP receptor antagonists AH6809 and 868C84. Results obtained for β-thromboglobulin release were inconclusive since both AH6809 and 868C84 inhibited release to a similar extent as did PGD(2), indicating that a limited effect either on aggregation or TXB(2) formation does not preclude a greater effect on degranulation.