Effect of chronic ketanserin treatment on serotonin-induced platelet aggregation in patients with Raynaud's phenomenon

Serotonin and serotonin antagonism in cardiovascular and non-cardiovascular disease

Serotonin, or 5-hydroxytryptamine, is a naturally-occurring vasoactive substance found primarily in the brain, enterochromaffin tissue, and blood platelets. It has diffuse cardiophysiologic effects. The multiple effects of serotonin on blood vessels can be explained by the existence of 2 serotonergic receptor subtypes (the S1 receptor mediates vasodilation, and the S2 receptor vasoconstriction). Serotonin via the S2 receptor also augments the actions of several other vasoconstricting substances. Serotonin may be responsible for causing, or at least perpetuating, some forms of systemic hypertension through peripheral and central nervous system (CNS) actions. Ketanserin is a highly selective S2-serotonergic antagonist with additional alpha-adrenergic blocking activity, which has been proposed as a therapy for various cardiovascular diseases including hypertension. It has been shown to be more effective than placebo in treating hypertension and comparable in effectiveness to other antihypertensive drugs. Its major side effects relate to the CNS, and prolongation of the electrocardiogram QT interval has been described. Caution must be used when using ketanserin in patients receiving potassium- and magnesium-losing agents, because of the risk of torsades de pointes. Ketanserin has potential utility in the treatment of eclampsia, peripheral vascular disease, carcinoid syndrome, and "shock lung." The drug is not yet approved for clinical use in the United States.

The effects of a selective 5-HT2 receptor antagonist (ICI 170,809) on platelet aggregation and pupillary responses in healthy volunteers

1. ICI 170,809 (2-(2-dimethylamino-2-methylpropylthio)-3-phenylquinoline hydrochloride) is a potent 5-hydroxytryptamine (5-HT) type 2 postsynaptic receptor antagonist. 2. Effects of ICI 170,809 as single oral doses (3, 7, 15 and 30 mg) or placebo were studied on the duration of antagonism for the ex vivo platelet aggregatory response to 5-HT and to the pupillary light constrictor response in eight healthy male volunteers. 3. Pupillary dark adapted responses to a 0.5 s light stimulus were measured using a portable infrared pupillometer, for up to 24 h after dosing. 4. The in vitro platelet 5-HT aggregation response was reduced by ICI 170,809, with depression of the dose-response curve to 5-HT at all concentrations of 5-HT and with no evidence for a parallel shift. 5. The ex vivo platelet 5-HT response demonstrated a dose related significant (P less than 0.02) decrease in aggregation reaching a maximum at 2 h after dosing with the effect persisting for at least 8 h after dosing with the 7 and 15 mg doses. 6. Resting pupil diameter (RPD), and light induced pupillary responses in the dark adapted pupil, showed a significant (P less than 0.01) dose related reduction with significant (P less than 0.05) effects still present with the 15 and 30 mg doses at 8 h after dosing. 7. We conclude that, changes in both ex vivo platelet aggregation to 5-HT and dark adapted pupil size, are significantly correlated (P less than 0.0001) with log plasma concentrations (ng ml-1) of ICI 170,809, enabling the assessment of 5-HT2-receptor antagonism in man.

Digital blood flow and 5-hydroxytryptamine receptor blockade after ketanserin in patients with Raynaud's phenomenon

1. The effect of ketanserin on digital blood flow and 5-hydroxytryptamine (5-HT)-induced platelet aggregation was studied in 18 patients with Raynaud's phenomenon. 2. Measurements were made before and after a single dose of 20 mg ketanserin and again after 1 month of continuous treatment with 20 mg ketanserin three times a day. 3. Digital blood flow was assessed by changes in digital pulse volume; platelet aggregation by changes in light transmission after challenge with 10(-5) M 5-HT. 4. Ketanserin induced a rise in digital blood flow and blocked the platelet response to 5-HT; the two events were not correlated and were independent of subjective improvement. 5. These data do not support the suggestion that 5-HT2-receptor blockade is of major importance in the dilatory effect of ketanserin in Raynaud's phenomenon.