Abnormal platelet aggregation in patients with Raynaud's phenomenon

Platelet aggregation in vitro to several aggregating agents (serotonin (5-HT), adenosine diphosphate, adrenaline and collagen) was studied in 16 patients with primary and secondary Raynaud's phenomenon and compared with that in 13 normal volunteers. Platelets from patients with Raynaud's phenomenon had significantly greater responses to all the 5-HT concentrations tested (p <0.001 for 10 μM; p <0.01 for0 1 μM; p <005 for 0 01 μM; p <0 02 for 0 025 μM) and to low doses of adenosine diphosphate (p <0.01 for 0 1 μM; p <0 02 for 0 5 μM) but normal responses to collagen, adrenaline, and high doses of adenosine diphosphate. Patients with secondary Raynaud's phenomenon were significantly more hypersensitive to 0 5 μM adenosine diphospate than patients with primary Raynaud's phenomenon. In patients with secondary Raynaud's phenomenon there was a significant correlation between the extent of 5-HT aggregation and the duration of the disease. The finding that platelets from patients with Raynaud's phenomenon have enhanced responses to 5-HT and adenosine diphosphate, but normal responses to adrenaline and collagen, is consistent with a role for 5-HT in this disease.