Increased platelet aggregation in patients receiving chlorpromazine: responses to 5-hydroxytryptamine, dopamine and N-dimethyl dopamine.

Platelet aggregation responses to 5-HT, dopamine, N-dimethyl dopamine and adenosine diphosphate were compared in normal subjects and patients treated with chlorpromazine (CPZ) for longer than 6 months. We confirmed our previous finding that 5-HT induced aggregation is enhanced in CPZ treated patients. Increased aggregation responses were also observed with dopamine and N-dimethyl dopamine. Quantitative comparisons of aggregation rates and total changes in optical density of platelet rich plasma relative to adenosine diphosphate showed significant increases with 5-HT, dopamine and N-dimethyl dopamine. Implication of dopaminergic mechanisms in the central effects of phenothiazines suggests that changes in dopamine induced aggregation responses may be useful in attempting correlations of clinical and pharmacological effects.