MULTIPLE AGONIST INDUCTION OF AGGREGATION - AN APPROACH TO EXAMINE ANTI-AGGREGATING EFFECTS IN-VITRO

We tested the hypothesis that utilisation of multiple agonists in phys iological concentrations is more appropriate for platelet aggregation in vitro than a single agonist in high concentration, Utilising impeda nce aggregometry in whole human blood (normal subjects and patients wi th coronary artery disease) we observed potentiation of pro-aggregator y effects of ADP by the combination of adrenaline, serotonin and throm bin in subthreshold concentrations (multiple agonist approach), In blo od samples from the patients, verapamil (Ver, an L-type Ca2+ channel b locker), nitroglycerine (NTG, a stimulator of cGMP formation) and pros taglandin E(1) (PGE(1), a stimulator of cAMP formation) inhibited plat elet aggregation in vitro, With NTG and PGE(1), there was increased se nsitivity to multiple agonists in comparison with ADP alone. For examp le, inhibition of aggregation with 10(-4)M NTG increased from 37 +/- 5 % with ADP alone to 86 +/- 13% (P < 0.01) with multiple agonists. Thre shold effects of NTG were seen at 10(-6)M with ADP alone and 10(-7) M with multiple agonists; whilst threshold for PGE(1) was reduced from 1 0(-10) to 10(-11)M, However, responses to Ver were unchanged by multip le agonists, demonstrating that the potentiation of anti-aggregating e ffects utilising the multiple agonist approach is not a non-specific p henomenon, The ability of multiple agonists to enhance the anti-aggreg ating effects of NTG and PGE(1) provides an in vitro experimental meth od mimicking the in vivo situation.