Intracellular sodium and calcium during antihypertensive treatment.

In 49 untreated essential hypertensives the effects of the loop diuretic, piretanide, in a dose of 12 mg daily (n = 14) and of 6 mg daily (n = 18) as well as of beta blockers (pindolol, metipranolol, atenolol, n = 17) on blood pressure, intracellular Ca++ and Na+ activity in red blood cells were examined. Intracellular ion activities were measured by ion-selective electrodes. The higher dose of piretanide caused a decrease of intracellular Ca++ activity and an increase of intracellular Na+ activity. Under the lower dose of piretanide there was a comparable decrease of intracellular Ca++ activity but no significant change of intracellular Na+ activity. Beta blockers decreased intracellular Ca++ activity but left intracellular Na+ activity unchanged. It is concluded that intracellular free Ca++ plays an important role in the regulation of vascular tone in essential hypertension. There seems to be no direct relation between intracellular free Na+ and blood pressure under antihypertensive therapy.