Platelet content of serotonin and response to stress.

As a source of peripherally available vasoactive agents, platelets may play a role in many cardiovascular events. This study aimed to assess the functional role of serotonin released by platelets in mediating the effects of sympathetic stimulation on vascular tone in healthy subjects. Platelet serotonin (5-HT) content and plasma catecholamine concentrations were measured by high performance liquid chromatography with electrochemical detection in blood samples drawn from 10 healthy subjects undergoing tilt test, cold pressor test, treadmill and isometric exercise by handgrip. It was possible to identify both responder subjects who showed a significant decrease in 5-HT platelet content and non-responder subjects who showed no significant change. Stress-induced increases in plasma catecholamine levels were higher in the responders. This suggests that some subjects were more susceptible to adrenergic stimuli and that the elevated concentrations of circulating catecholamines may induce platelet activation and 5-HT release. Analysis of the cardiovascular responses to the tests suggests that 5-HT released by platelets upon adrenergic stimulation in healthy subjects might induce a vasodilatory response modulating sympathetic tone.