Methods and findings in experimental and clinical pharmacology vol:14 issue:3 pages:211-7
The effects of naftopidil on the intracellular concentration and transmembrane fluxes of Na+ and K+ in erythrocytes and on the intracellular Na+, K+ and free cytosolic Ca2+ concentration in platelets were studied in twenty-four normal male subjects, using a double-blind study design. After a run-in period on placebo for 1 week, the subjects were treated with either placebo (n = 8) or naftopidil 25 mg (n = 8) or 50 mg (n = 8) once a day for 4 weeks. Intraerythrocyte Na+ concentration and the erythrocyte anion carrier were decreased during naftopidil administration. No significant effect of naftopidil could be demonstrated on ouabain-sensitive Na+ efflux, bumetanide-sensitive Na+ efflux, ouabain, bumetanide-resistant Na+ and K+ efflux and Na+, Li(+)-countertransport activity in red blood cells or on the intraerythrocyte K+ and Mg2+ concentration. The free cytosolic Ca2+ and Na+ concentration in platelets was also decreased during naftopidil administration while no effect of naftopidil was found on the intracellular K+ and Mg2+ concentration in platelets.