ALTERATIONS IN ATRIAL-NATRIURETIC-PEPTIDE (ANP) SECRETION AND RENAL EFFECTS IN AGING

Aging is associated with hypertension and electrolyte disturbances. Th e purpose of this study was to determine the effect of aging upon secr etion and renal actions of atrial natriuretic peptide (ANP). Rats were anesthetized and received tracheal, jugular rein, carotid artery, and bilateral uretheral catheterization. One set of young (2-3 mo) rats ( Group 2, n = 9) and one set of old (18-21 mo) rats (Group 4, n = 7) re ceived bilateral atrial appendectomies. Control young (Group 1, n = 8) and old (Group 3, n = 8) rats received a sham appendectomy. All rats were infused (iv) with 6% albumin in Krebs buffer sufficient to increa se blood volume by 15%. Finally each rat was injected with ANP (1 mu g /kg). Sodium excretion rate (UNa+V) in response to volume expansion wa s significantly decreased in all groups compared to Group 1 (young con trol, p<.05). All groups demonstrated a striking increase in UNa+V wit h the ANP injection, but the response was greatest in young control ra ts when factored by body weight (p<.05). There were no significant dif ferences in MAP between the groups, suggesting that the differences in UNa+V observed were not the result of hemodynamic factors. Isolated p erfused atria from young (n = 9) a,ld old (n = 8) mrs were subjected t o stretch and endothelin stimulation (50 nM). Atria from young rats sh owed a dramatic increase in ANP secretion in response to atrial stretc h and a further marked increase in secretion in response to endothelin , whereas both of these responses were markedly attenuated in old rats (p<.05). These results suggest that the secretion and renal effects o f ANP are impaired in aging. Changes in secretion and actions of ANP i n aging could contribute to the development of hypertension or heart f ailure.