The effects of the 5 HT2 antagonist ritanserin on blood pressure and serotonin-induced platelet aggregation in patients with untreated essential hypertension.

We have given the selective 5 HT2 antagonist ritanserin in a dose of 10 mg twice daily for 4 weeks in a double-blind, randomized, placebo-controlled, parallel group study of 18 patients with untreated essential hypertension. The fall in single platelet count due to 5 HT-induced platelet aggregation was significantly reduced by ritanserin compared with placebo (p less than 0.05). There were no significant changes in supine or erect blood pressure or heart rate after ritanserin compared to placebo. Forearm blood flow, measured by mercury-in-strain gauge venous occlusion plethysmography, was not significantly altered by ritanserin. Ritanserin caused prolongation of the QTc interval by 41 (SEM 11) ms (p less than 0.05 compared to placebo) but had no detectable effect on QRS duration, features suggestive of Class III antiarrhythmic activity. These findings do not support an independent role of the 5 HT2 receptor in maintaining raised arterial pressure in essential hypertension.