No abstract

Ketanserin is a well-known serotonin S₂ receptor antagonist but its capacity to inhibit serotonin-induced aggregation ex vivo during chronic administration has been a matter of debate. In vitro evidence is presented that the inhibitory capacity of ketanserin is lowered by increasing plasma pH. Since the pH of plasma kept at the open air increases with time, we studied the effect of chronic administered ketanserin on serotonin-induced platelet aggregation in plasma kept at a lowered pH of 7.70, by replacing the air with 95% O₂–5% CO₂. Using this slightly modified technique, we could, in contrast to our previous studies, observe a complete inhibition of the serotonin-induced aggregation throughout the ketanserin treatment period.