Hormonal and renal responses to atrial natriuretic peptide infusion in low-renin hypertension

Although atrial natriuretic peptide (ANP) levels are often elevated in lowrenin hypertensives, the renal and hormonal effects of ANP infusion have never been evaluated in these patients. To address this topic, 27 lean nondiabetic men affected by uncomplicated essential hypertension were studied. Low-renin patients (n = 9, age 42 ± 3 years) were defined as those individuals in balance on a low NaCl intake (10 mmol NaCl/day for 1 week) who had a plasma renin activity <0.30 ng angiotensin I/l/s, in both the supine and the upright positions. The remaining hypertensives (n = 18, age 41 ±4 years) were classified into the normal-renin group. Six age-matched healthy men (age 40 ± 2 years) served as controls. After plasma renin activity determinations, both patients and controls were replaced on a normal NaCl intake (120 mmol NaCl/day). After 1 week, either ANP (99-126), at a dose(0.7 pmol/kg/min for 3 h) which is known to induce changes in plasma AN P confined to the range of normality, or its vehicle were infused at 1-week intervals, according to a randomized double-blind crossover design. At time 0, low-renin patients had significantly higher (p < 0.05) levels of plasma ANP (12.4 ± 2.5 fmol/ml) than normal-renin patients (7.2 ± 2.4 fmol/ml) and normotensives (7.4 ± 3.3 fmol/ml). The ANP-related aldosterone decrement was more rapid (p<0.05 at 30 min) and evident in low-renin patients (from 325.3 ± 12.3 pmol/l at time 0 to 207.7 ± 8.3 at 180 min; p < 0.001) than in normal-renin patients (from 352.6 ± 4.5 pmol/1 at time 0 to 282.6 ± 11.3 at 180 min; p < 0.01) and control subjects (from 300.5 ± 10.3 pmol/1 to 270.6 ± 12.8 at 180 min; p<0.05). As compared with placebo, ANP significantly increased renal sodium excretion in all groups, but low-renin patients had a greater ANP-induced increase in natriuresis (p < 0.05 at 120 min) than normal-renin hypertensives (NS) and control subjects (NS). The glomerular filtration rate increased during ANP infusion in low-renin patients (p < 0.05 at 60 min). while no significant changes were observed in normal-renin hypertensives and normotensives. In conclusion, at variance with other conditions, such as cardiac failure and liver cirrhosis, in hypertensive patients the presence of increased levels of plasma ANP does not imply a reduction in the renal and endocrine responses to ANP infusion. © 1995 S. Karger AG, Basel.