REDUCED RENAL HEMODYNAMIC-RESPONSE TO ATRIAL-NATRIURETIC-PEPTIDE IN ELDERLY VOLUNTEERS

Aging is associated with decreased ability to excrete salt and water, thus increasing the susceptibility to volume overload in older individuals. Meanwhile, plasma levels of atrial natriuretic peptide (ANP) increase progressively with age for unknown reasons. We compared the natriuretic and renal hemodynamic responses to low-dose ANP infusion in an elderly group of volunteers (mean age, 74 years) with those of a group of younger subjects (mean age, 29 years). A significant reduction below baseline values in effective renal plasma flow occurred in the young group after the 2-hour peptide infusion (657 ± 125 υ 476 ± 92 mL/min [mean ± 1 SD]) when compared with the elderly group (two-way analysis of variance; P < 0.02). A concomitant increase in renal vascular resistance was noted in the young group only during the same period (6,631 ± 1,384 υ 9,136 ± 2,126 dyn s cm2 x 106). This increase was also significantly higher than that in the elderly group (analysis of variance; P < 0.02). Both groups demonstrated similar natriuretic responses. Absolute sodium excretion had increased significantly above baseline values in both young and elderly subjects at the end of the 2-hour peptide infusion (111 ± 25 μmol/min to 183 ± 33 μmol/min υ 107 ± 23 μmol/min to 198 ± 56 μmol/min) and remained elevated until 1 hour postinfusion. We conclude that the elderly subjects in our study demonstrated a diminished renal hemodynamic response to infusion of ANP while preserving a natriuretic response similar to that found in the younger subjects. The present results lend no support to the hypothesis that a diminished diuretic response to salt loading in the elderly results from a reduced natriuretic response to ANP. The diminished hemodynamic response may either reflect downregulation of ANP vascular receptors with increasing age or may result from age-related changes in the renal arterioles. © 1993, National Kidney Foundation. All rights reserved. All rights reserved.