Increased atrial natriuretic factor prohormone peptides with aging in the heart, but not in lung, liver, or intestine.

Atrial natriuretic factor (ANF) has been found to be increased in the circulation of aged rats. The present investigation was designed to determine if the N-terminal ANF prohormone peptides with blood pressure lowering properties are increased in the circulation of "aged" (24-26 months) versus "adult" (4-6 month old) Fisher 344 rats. We utilized two sensitive and specific radioimmunoassays that immunologically recognize the 98 amino acid (a.a.) N-terminus (proANF 1-98) and a.a. 31-67 (proANF 31-67, Vessel dilator) from the midportion of the N-terminus of the 126 a.a. ANF prohormone. ProANF 1-98, and proANF 31-67, as well as ANF, were found to be elevated in the circulation of aged versus adult animals with proANF 31-67 and ANF elevations being significant at p < 0.05. To determine the potential source of the increased atrial natriuretic peptides in aged animals four tissue sources (liver, lung, heart, and intestine) from both adult and aged animals were examined. Hearts of aged animals contained significantly (P < 0.05; ANOVA) more proANF 1-98, proANF 31-67, and ANF than hearts of adult animals. There was no significant difference in the concentration of proANF 1-98, proANF 31-67, or ANF in the lung, liver, or intestine of the aged versus the adult animals. These results indicate that aged animals contained increased N-terminal and C-terminal ANF prohormone peptides in the circulation. The source of these increased peptides appears to be the heart.