The effects of calcium channel blockade on blood pressure and calcium metabolism.

To study the relation of calcium channel blockade to calcium metabolism, we measured serum ionized calcium (Ca++i0), magnesium (Mg), calcitonin (CT), and 1,25-dihydroxyvitamin D (1,25-D) before and after short-term therapy with verapamil 120 mg three times daily in essential hypertensive subjects on low (10 mEq) and high (200 mEq) dietary sodium intakes. Salt-sensitive compared with salt-insensitive subjects on high v low dietary salt intake had lower Ca++i0 (P less than .05), higher 1,25-D (P less than .02), and a greater hypertensive responsive to verapamil (% delta DBP = 17.7 v -8.2, P less than .05). The % delta DBP was related to the initial CT (r = 0.68, P less than .05), initial 1,25-D (R = -0.89, P less than .01), and to the drug-induced % delta 1,25 D (R = .60, P less than .05). Thus, lower initial calcium and calcitonin levels, higher initial levels of 1,25-D, and a greater drug-induced suppression of 1,25-D were associated with an enhanced hypotensive response to verapamil. Verapamil elevated Ca++i0 (2.46 +/- 0.04 to 2.53 +/- 0.04 2.00 mEq/L, P less than .05), and suppressed Mg (2.00 +/- 0.03 to 1.84 +/- 0.03 mEq/L, P less than .01) and 1,25-D levels (66.7 +/- 8.1 to 51.6 +/- 5.7 pg/mL, P less than .05). These results suggest interactive effects of sodium and calcium metabolism in essential hypertension, especially among salt-sensitive individuals. We conclude that alterations of calcium metabolism may underlie the sensitivity to verapamil therapy and may contribute to its hypotensive effects.