Cell membrane cation transport systems during aldosterone antagonism.

We conducted a double-blind, placebo-controlled parallel study of the effect of the aldosterone antagonist spironolactone, administered once daily for 1 week to normal male subjects, on blood pressure, intracellular cationic concentrations, and transmembrane cation transport systems and plasma or urinary variables. After a 1-week run-in period on placebo, the subjects (n = 40) were allocated to a placebo or a spironolactone group. Placebo or 100 mg spironolactone was administered once daily in the morning for 1 week. All subjects were investigated at baseline and after 1 week of placebo or spironolactone administration. Standing systolic blood pressure of subjects in the spironolactone group was decreased (p < 0.001) as compared with that of subjects in the placebo group, but standing diastolic blood pressure did not change. Decreased intraerythrocyte and intraplatelet Na+ and free Ca2+ concentration and decreased activity of the platelet Na(+)-pump activity were observed in the spironolactone-treated subjects. The intraerythrocyte and intraplatelet K+ and Mg2+ concentrations, as well as the activities of the erythrocyte Na+, Li(+)-countertransporter and Na+, K(+)-cotransporter, and Na+ and K+ leakage, were not changed during spironolactone administration. The blood pressure-lowering action of spironolactone in men in the standing position is accompanied by a decrease in cytosolic free platelet Ca2+ concentration, by a reduction in intraplatelet and intraerythrocyte Na+ concentration, and in the platelet Na+ pump activity.