Abstract
To investigate the ability of the ageing heart to release atrial natriuretic peptide (ANP) we compared the response of awake, trained, chronically catheterized old (20–21 months) and young; (4 months) rats to an acute, hypertonic saline challenge. There were no differences between young and old rats in basal plasma concentration of sodium (P Na; old: 141 ± 3 meq/l; young 143 ± 3 meq/l) or ANP (old: 61 ± 5 pg/ml; young: 67 ± 12 pg/ml. Five minutes after acute saline challenge, P Na rose in both groups (old: 146 ± 2 meq/l; young 149 ± 1 meq/l) and approximately 3-fold increases in plasma ANP levels (182 ± 24 pg/ml; young: 179 ± 42 pg/ml). Hearts of old and young rats were assayed for atrial and ventricular ANP content. Atrial ANP levels were similar in old and young rats (13.5 ± 3.6 vs. 24.9 ± 8.7 μg/gl atrial tissue), whereas ventricular ANP content was ∼ 4-fold higher in old vs. young rats (153.7 ± 39.3 vs. 47.5 ± 6.4 ng/g ventricular tissue). Thus, the ageing rat heart responds equally as well as the young rat to an acute NaCl challenge.
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