Divalent cations in essential hypertension. Relations between serum ionized calcium, magnesium, and plasma renin activity.

We studied the relation of plasma renin activity to serum levels of ionized calcium and magnesium in 102 normotensive patients and in 98 patients with essential hypertension who were divided into low-renin, normal-renin, and high-renin groups. Serum magnesium levels were higher in patients with low-renin hypertension and lower in patients with high-renin hypertension than in those with normal-renin hypertension (P less than 0.025 for both comparisons) or in normotensive controls (P less than 0.005, P less than 0.05, respectively). In contrast, serum levels of ionized calcium were lower in patients with low-renin hypertension and higher in patients with high-renin hypertension than in those with normal-renin hypertension (P less than 0.001, P less than 0.05, respectively) or in normotensive controls (P less than 0.001, P less than 0.05, respectively). Altogether, the range of plasma renin activity in essential hypertension shows a continuous negative correlation with the serum magnesium level (r = -0.60, P less than 0.001) and a positive correlation with the serum ionized calcium level (r = 0.44, P less than 0.001). Accordingly, plasma renin activity in hypertension may reflect or contribute to changes in calcium and magnesium fluxes across cell membranes.