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.