Decreased nitric oxide levels and increased calcium content in platelets of hypertensive patients

Decreased levels of nitric oxide (NO) may contribute to impaired endotheliu m-dependent vasodilatation in essential hypertension. Moreover, in hyperten sion, major platelets aggregation and endothelial adhesion, and increased a therogenetic risks are also present. Nitric oxide produced by platelet NO s ynthase, which is similar to endothelial NO synthase, inhibits platelets ag gregation by increasing cytoplasmic cyclic GMP levels and contributes in a major way to the antithrombogenic properties of endothelium. The aim of thi s study was to investigate platelet NO production and cytosolic Ca2+ levels in patients with essential hypertension and in healthy subjects. We studie d NO production in 36 subjects (21 patients had essential hypertension and 15 subjects were normotensive); NO synthase activity was evaluated by measu ring nitrite levels by the Griess reaction in the supernatant of sonicated platelets. Cytosolic Ca2+ levels were measured in intact platelets using th e fluorescent probe Fura 2-AM. Nitric oxide levels in platelets were found higher in normotensive than in hypertensive patients (P < .0001). Nitric ox ide levels in hypertensive women were significantly higher than in hyperten sive men (P < .001). Hypertensive women and men had lower levels of nitrite than normotensive women and men (P < .001 and P < .002, respectively). Pla telet cytosolic Ca2+ levels were higher in hypertensive patients than in no rmotensive subjects (P < .001). An inverse correlation was found between pl atelet cytosolic Ca2+ and NO levels (r = 0.74, P < .002). These data confir m the link between hypertension and altered platelets function and suggest a role for NO in cardiovascular events. Moreover, the higher levels of nitr ic oxide in child-bearing age women than in men further support the protect ive effect of estrogens on cardiovascular diseases. (C) 2001 American Journ al of Hypertension, Ltd.