Effect of age on stretch-induced secretion of atrial natriuretic factor

Plasma atrial natriuretic factor (ANF) levels are known to be higher in aged rats and humans. Although this may be partially explained by a reduction in clearance from the circulation, it was not known whether the secretory nature of the atrial tissue also changes with age. We measured ANF release in response to atrial distention in young adult (2-3 months) and older retired breeder (4-6 months) male rats both in vivo (conscious instrumented animals) and in vitro (isolated perfused atria). Whereas increased intraluminal pressure caused a rise in ANF secretion when using atria derived from the younger rats, there was no such response when using atria derived from the older rats, i.e., stretch induced secretion was impaired. This appeared to be secondary to a reduction in atrial compliance in the older animals. Unlike previous studies, basal plasma ANF levels were lower in our retired breeders, although the response to volume loading was preserved. These results suggest that, already by about 6 months of age, the atrial tissue is less responsive to changes in atrial pressure. The increased plasma levels previously reported in senescent rats are therefore probably a result of reduced clearance rather than increased secretion.