Intracellular calcium in essential hypertension. A parameter for assessing effective antihypertensive treatment.

The effects of the loop diuretic piretanide on blood pressure and intra-erythrocytic free Na+ and Ca2+ were examined in 14 essential hypertensives. Intra-erythrocytic Ca2+ activity was found to decrease (P less than 0.01) and Na+ activity to increase (P less than 0.05). In spontaneously hypertensive rats (SHRs) hypovolaemia abolished the humoral transmission of hypertension to normotensive rats. Therefore the decrease in intracellular Ca2+, which may be responsible for the diminished vascular tone under diuretic treatment, could be mediated by a suppression of humoral factors due to diuretic-induced hypovolaemia.