Kinetics of atrial natriuretic peptide in young and elderly subjects

To study the influence of age on the kinetics of atrial natriuretic peptide (ANP) in man, human (99-126) ANP 2.0 micrograms.min-1 was infused IV for 60 min in 8 healthy young (18 to 25 y) and 9 healthy elderly (71 to 84 y) subjects. Both baseline ANP values and the levels at the end of infusion were higher in the elderly subjects. The mean residence time of ANP in the two age groups was not significantly different, whereas total body clearance (CL) was markedly diminished in the elderly as compared to the young subjects (mean +/- SD 3.1 +/- 1.0 l.min-1 and 6.2 +/- 4.1 l.min-1, respectively). The apparent volume of distribution at steady state was lower in the elderly than in the young, but the difference was not significant (mean +/- SD 44 +/- 19 and 103 +/- 111, respectively. The decrease in CL largely explained the higher ANP levels found in the elderly subjects. The MRT and the plasma half-life of the terminal phase did not differ between the two groups. In the elderly but not in the young subjects the calculated endogenous creatinine clearance was closely correlated with the CL (r = 0.90, P less than 0.001), thereby emphasizing the importance of the kidney in the metabolic clearance of ANP in the elderly.