ObjectiveTo determine whether sex influences the rate of sodium–proton (Na+-H+)-exchange-dependent swelling of platelets from patients with essential hypertension and normotensive controls.MethodPlatelet swelling was detected by measuring the change in optical density of platelet suspensions added to sodium propionate buffer, pH 6.7, at 37°C. We studied 56 subjects, 28 men and 28 women, each group containing 14 normotensive and 14 hypertensive subjects. The groups were well matched for sex, ethnicity and age.ResultsThat platelet swelling was dependent on Na+-H+exchange was demonstrated by performing blockade by 5-(N,N-hexamethylene)-amiloride and by measuring its dependence on extracellular Na+concentration. The rate of swelling of platelets from hypertensive men [(14.2 ± 0.9) × 10−3/s] was higher than that of those from normotensive men [(10.1 ± 0.5) × 10−3/s], normotensive women [(10.0 ± 0.5) × 10−3/s] and hypertensive [(11.1 ± 0.8) × 10−3/s] women. The interaction between sex and hypertension was significant (P< 0.05 by analysis of variance).ConclusionsSex influences the effect of hypertension on the rate of swelling of platelets exposed to sodium propionate (pH 6.7).