To examine effects of age on basal and sodium-stimulated plasma concentrations and atrial contents of atrial natriuretic factor (ANF), young (2 mo), mature (4 mo), and older adult (12-18 mo) rats were maintained on a low-sodium diet (< .05% by weight) for 8 days. Half of each group then received a high-sodium diet (3.1%) for 24 hours before sacrifice. Mean plasma ANF concentrations were greater in the older adult rats, 506 ± 287 pg/ml, than in young or mature rats, 262 ± 182 and 150 ± 40pg/ml, respectively (p < .001). Age-related increases in plasma ANF concentration and left atrial ANF content (p < .001) were present in both low- and high-sodium fed rats. Significant differences in plasma and atrial ANF levels between low- and high-sodium fed rats were noted only in older adult rats, where an inverse correlation (r = -.425, p < .05) was observed between plasma and left atrial ANF levels. These observations demonstrate that plasma and atrial ANF levels increase with age in the rat. With aging, increased ANF effects may modulate other systems regulating cardiovascular homeostasis.
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