Acute effects of nifedipine on renal electrolyte excretion in normal and hypertensive subjects

The role of atrial natriuretic peptide in the diuretic effect of Ca2+ entry blockers

The effect of three calcium entry blockers--verapamil, nifedipine and felodipine--on diuresis, natriuresis, the renin-aldosterone axis, and atrial natriuretic peptide (ANP) levels was studied in 30 previously untreated patients with mild to moderate essential hypertension. All three blockers produced significant antihypertensive effects after 2 and after 24 h. Heart rate tended to decrease, but did not change significantly after verapamil, but increased significantly 1-2 h after nifedipine and felodipine. Plasma renin activity (PRA) did not change significantly with any treatment, and plasma aldosterone decreased with all three agents. ANP levels did not change significantly after verapamil, but increased significantly after nifedipine and felodipine. There was a significant positive correlation between the maximal change in ANP level and urinary sodium after nifedipine and felodipine. The increase in urinary sodium after verapamil was not significant. The role of the direct renal effect of calcium entry blockers in their persistent natriuretic action is discussed, as well as their short-term enhancement of ANP levels, which may account for the initial diuretic and natriuretic effects seen with this class of dihydropiridines.

Nitrendipine and renal tubular function in human volunteers

Nine normotensive, water-loaded subjects received 10 mg oral nitrendipine, and eight subjects received placebo in a double-blind randomized manner. Urine and plasma were collected at fixed time points for 1 hour before and for 4 hours after drug administration for biochemical measurements. Glomerular filtration rate was measured by inulin clearance and effective renal blood flow was measured by para-amino hippurate clearance. Absolute sodium excretion increased by 25.9% from 0.27 +/- 0.03 mmol/min to 0.34 +/- 0.02 mmol/min (P = .02), and fractional sodium excretion increased by 32.3% from 18.9 +/- 3.0% to 25.0 +/- 1.9% (P = .03) after nitrendipine, but both were unchanged after placebo. There was no change in inulin clearance, para-amino hippurate clearance, urine volume, or fractional excretion of uric acid, which made an effect on glomerular filtration, renal blood flow, or proximal tubular function an unlikely explanation of the natriuresis. Fractional excretion of magnesium increased after both placebo and nitrendipine administration, from 5.0 +/- 0.6% to 6.8 +/- 0.7% (P = .027) and 5.7 +/- 0.8% to 8.8 +/- 1.0% (P = .006), respectively. Fractional excretion of phosphate also increased after both placebo and nitrendipine, from 9.5 +/- 2.3% to 12.9 +/- 3.9% (P = .05) and 9.7 +/- 1.7% to 14.2 +/- 1.9% (P = .002), respectively. These changes are likely to be due to the effects of the water load rather than due to a drug effect. There was no change in clearance of solute free water, which made a direct effect on the loop of Henle or cortical diluting segment unlikely.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of nifedipine on plasma atrial natriuretic peptide in normal subjects and hypertensive patients

The physiology of atrial natriuretic peptide (ANP) secretion was studied in normotensive subjects and hypertensive patients both young and old. Basal plasma ANP concentration was least in young normotensives, intermediate in old normotensives and young hypertensives, and highest in old hypertensives. Nifedipine, a known stimulator of ANP secretion, acutely increased plasma ANP in young and old normotensive subjects but not in young hypertensive patients and half of the old hypertensive patients. Increase in serum ANP level in response to nifedipine did not augment its hypotensive effect. However, the increase of aldosterone in response to nifedipine-induced rise in plasma renin activity (PRA) seemed to be suppressed by elevated ANP.