[In vivo platelet activation in mild arterial hypertension]

In order to investigate whether an altered "in vivo" platelet serotonin release contributes to the low platelet serotonin content observed in essential hypertensive patients, we have measured plasma concentrations of beta-thromboglobulin and platelet factor 4, urinary beta-thromboglobulin concentrations and platelet serotonin and platelet factor 4 contents in 11 untreated essential hypertensive patients (WHO Stage I) and in 12 age-matched normotensive controls. Beta-thromboglobulin and platelet factor 4 are specific platelet proteins localized in the alpha-granules which are released during in vivo platelet activation. Plasma and urinary concentrations of these alpha granule proteins determined by radioimmunoassay were found to be similar in hypertensive and normotensive subjects. The low platelet serotonin content determined by high pressure liquid chromatography from platelet rich plasma in hypertensive patients (0.282 +/- 0.008 vs 0.348 +/- 0.019 nmol/10(8) platelets, p less than 0.01) was not associated with a decrease in platelet 4 content (1.36 +/- 0.07 vs 1.36 +/- 0.10 microgram/10(8) platelets). This study shows that platelet alpha-granule content is unaltered in uncomplicated essential hypertension and suggests that the low platelet serotonin content in hypertensives is mainly due to the inhibition of platelet serotonin uptake.