Increased bioactivity of rat atrial extracts: Relation to aging and blood pressure regulation

The purpose of this study was to evaluate the possible role of atrial facto r(s) in the regulation of cardiovascular homeostasis and their relationship to aging. Rats were anesthetized and received jugular vein, carotid artery , and bilateral ureteral catheterization. After a half-hour equilibration p eriod, the rats received 0.5 ml of atrial extract with a concentration of p roANP (atrial natriuretic peptide) of 150 mug/ml prepared from either aged (18-20 month, "aged extract group", n = 12) or young (2-3 month, "young ext ract group", n = 12) rats. Mean arterial pressure (MAP) and renal function were monitored ol er five 20-minute periods. The atrial extract caused MAP to fall significantly in the aged extract group (p <.05) but MAP was unchan ged in young extract group. There was a significant difference in MAP betwe en the two groups (p <.05). Urine output increased significantly in both gr oups after extract infusion (p <.05 in both cases). Sodium and potassium ex cretion showed similar responses. However, the diuresis, natriuresis, and k aliuresis after extract infusion would have been expected to be relatively lower in the aged extract group compared to the young extract group conside ring the significantly lower MAP in the aged extract group. High performanc e gel permeation chromatography (HP-GPC) analysis of the atrial extract sho wed an increased quantity of a large molecular weight C-terminal peptide in atrial extracts from aged rats compared to young rat atria. Plasma levels of ANP and proANP 1-30 both increased significantly after extract infusion in both aged and young groups, and there was no significant difference in A NP concentration between the two groups. However, the concentration of proA NF 1-30 was significantly increased in the aged group compared to the young group after extract infusion. These results suggest that changes in the st ructure or processing of proANP in aging may contribute to the different he modynamic responses.