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 infusio n have never been evaluated in these patients. To address this topic, 27 lean nondiabetic men affected by uncomplicated essential hypertensi on were studied. Low-renin patients (n = 9, age 42 +/- 3 years) were d efined as those individuals in balance on a low NaCl intake (10 mmol N aCl/day for 1 week) who had a plasma renin activity <0.30 ng angiotens in I/I/s, in both the supine and the upright positions. The remaining hypertensives (n = 18, age 41 +/- 4 years) were classified into the no rmal-renin group. Six age-matched healthy men (age 40 +/- 2 years) ser ved as controls. After plasma renin activity determinations, both pati ents 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 f or 3 h) which is known to induce changes in plasma ANP 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, lo w-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 fmo l/ml) and normotensives (7.4 +/- 3.3 fmol/ml). The ANP-related aldoste rone decrement was more rapid 0,< 0.05 at 30 min) and evident in low-r enin patients (from 325.3 +/- 12.3 pmol/l at time 0 to 207.7 +/- 8.3 a t 180 min; p < 0.001) than in normal-renin patients (from 352.6 +/- 4. 5 pmol/l at time 0 to 282.6 +/- 11.3 at 180 min; p < 0.01) and control subjects (from 300.5 +/- 10.3 pmol/l to 270.6 +/- 12.8 at 180 min; p < 0.05). As compared with placebo, ANP significantly increased renal s odium excretion in all groups, but low-renin patients had a greater AN P-induced increase in natriuresis (p < 0.05 at 120 min) than normal-re nin hypertensives (NS) and control subjects (NS). The glomerular filtr ation rate increased during ANP infusion in low-renin patients (p < 0. 05 at 60 min), while no significant changes were observed in normal-re nin hypertensives and normotensives. In conclusion, at variance with o ther conditions, such as cardiac failure and liver cirrhosis, in hyper tensive patients the presence of increased levels of plasma ANP does n ot imply a reduction in the renal and endocrine responses to ANP infus ion.