Aim\ To investigate the effects of single dose of captopril on intracellular free calcium concentration(
i) of platelets
and relationship between the activation of platelets and the progression of hypertension in hypertensive patients.\ Methods\ The resting i of platelets was measured in 102 essential hypertensives(EHT),of which 52 cases were orally given a single dose of captopril.\ Plasma renin activity(PRA), angiotensin Ⅱ(AngⅡ) concentration and i of platelets were monitored before and 1 hour after administration.\ Results\ It was found that the basal i level of platelets was significantly higher in the patients with EHT than in normal controls,and was steadly increased with the progression of hypertension.\ The blood pressure,plasma AngⅡ,and resting Ca 2+ of platelets were markedly decreased 1 hour after administration of a single dose of oral captopril,while PRA was significantly increased.\ There were weak correlations between the decreases in mean BP and the decreases in the Ca 2+ of platelets(r=0 36,P<0 01),and the decreases in plasma AngⅡ(r=0 38).\ A weak correlation between the changes in plasma AngⅡ and the decrease in Ca 2+ was also noted(r=0 37,P<0 01).\ No significant correlation was found between plasma AngⅡ and the resting level of Ca 2+ of platelets.\ Conclusion\ Platelets are activated in the patients with hypertension and the activation of plateletes are paralelled with the progression of hypertension.\ Plasma AngⅡ seems responsible neither for the maintainance of basal level nor for the changes of Ca 2+ of platelets after administration of oral captopril in the hypertensives.