Effects of captopril and of other antihypertensive drugs on cell membrane ion transport--a preliminary report.

We measured red blood cell Na+-K+ pump, Na+-Li+ countertransport and Na+-K+ cotransport activities, together with intraerythrocyte sodium content before and after 3 months therapy with captopril and two other antihypertensive drugs (atenolol and canrenoate potassium) in subjects suffering from essential hypertension. All patients discontinued any previous treatment at least 3 months before the basal evaluation of cell membrane activities. All three drugs significantly lowered blood pressure but only captopril and canrenoate potassium induced significant modifications in red blood cell parameters. After three months of captopril therapy intraerythrocyte Na+ content was significantly decreased (P less than 0.01) without any detectable change in cation transport system activity. After 3 months of canrenoate potassium therapy we also observed a significant decrease in internal Na content (P less than 0.01), together with a significant increase in Na+-K+ pump (P less than 0.02) and Na+-Li+ countertransport (P less than 0.05) activities.