Body sodium-blood volume state, aldosterone, and cardiovascular responsiveness after calcium entry blockade with nifedipine.

Exchangeable sodium, blood volume, plasma norepinephrine (NE), epinephrine, renin and aldosterone levels, and pressor responses to infused NE or angiotensin II (AII) were assessed in ten patients with essential hypertension on placebo, following 6 to 8 weeks of calcium-antagonist nifedipine (NIF), 3 X 10 to 20 mg/day, and after 6 to 8 weeks on NIF combined with the diuretic chlorthalidone (CHLOR), 25 to 50 mg/day. Pressor effects of infused calcium also were evaluated on placebo and NIF. Supine blood pressure was decreased from 151/97 +/- 5/2 (SEM) to 132/88 +/- 6/2 mm Hg after NIF alone (P less than 0.05) and to 124/83 +/- 7/3 mm Hg after NIF + CHLOR (P less than 0.01). Body wt was increased from 72.7 to 73.9 kg on NIF alone (P less than 0.05), but decreased to 72.1 (P less than 0.05 compared with placebo) after adding CHLOR. Exchangeable sodium also rose from 2642 +/- 237 to 3360 +/- 266 mmoles on NIF (+ 27%; P less than 0.01) and returned to control values (2638 +/- 248 mmoles) after addition of CHLOR. Plasma volume was only slightly modified on NIF (from 2621 +/- 193 to 2751 +/- 160 ml; + 5%), but was reduced to 2232 +/- 231 ml on NIF + CHLOR (P less than 0.05). Responses of circulating aldosterone to AII were similarly diminished (P less than 0.01) during both conditions. Heart rate, supine and upright plasma renin, aldosterone and catecholamine levels, and pressor responses to NE, AII, or calcium were not consistently changed.(ABSTRACT TRUNCATED AT 250 WORDS)