Abstract
The ability of N-methyl-1,2-diphenyl ethanolamine (compound M), N-isobutyl-1,2-diphenyl ethanolamine (compound E), diltiazem and verapamil to inhibit in vitro ADP-induced platelet aggregation was examined in rat platelet-rich plasma. Pretreatment of the platelets with the compounds (0.1-3 mM) for 3 min at 37-degrees-C, inhibited an ADP-induced aggregation in a concentration-dependent manner. The maximum percentage inhibitions induced by compounds M, E, diltiazem and verapamil were: 95.5 +/- 6.5, 98.4 +/- 7.5, 100 and 95.9 +/- 8.3 % at concentrations of 3, 0.64, 0.96 and 0.4 mM, respectively (n = 8 - 12). The inhibitory dose 50 (ID50) values for compounds M, E, diltiazem and verapamil were 1.3 +/- 0.13, 0.29 +/- 0.01, 0.44 +/- 0.03 and 0.2 +/- 0.01 mM, respectively. The antiaggregatory effects were not antagonized by methylene blue (50-200-mu-M), but were completely antagonized (> 95%) by elevation of the Ca2+ level in the platelet-rich plasma by 0.2-0.7 mM. Co-administration of (-)propranolol (17-mu-M) with anyone of the compounds enhanced the antiaggregatory effects. The compounds (0.1-0.2 mM) enhanced the prostacyclin (0.01 nM)-induced antiaggregatory activity. The antiaggregatory effects of the compounds are likely to be due to an inhibition of influx of Ca2+ into the platelets.