Intracellular electrolytes during antihypertensive treatment with a loop diuretic.

The effect of the loop diuretic, piretanide (12 mg/day on blood pressure and intracellular electrolyte composition in red blood cells during a six-week treatment period was studied in 14 previously untreated essential hypertensive patients. Blood pressure fell continuously during the six weeks, intracellular Na+ activity in red blood cells increased slightly (P less than 0.05), and there was a marked decrease in intracellular Ca2+ activity (P less than 0.01). Intracellular K+ concentration was not altered. It is concluded therefore, that intracellular free Na+ does not correlate with the actual blood pressure, whereas the fall in blood pressure is associated with a decrease in intracellular free Ca2+, suggesting that intracellular free Ca2+ is involved in the regulation of vascular tone.