The biological and immunological properties of fractionated atrial extracts from young and old rats.

Abstract We have previously reported that the biological activity of rat atrial extract declines with age. The present study was undertaken to further evaluate the natriuretic, hypotensive and immunological properties of fractionated and HPLC purified atrial extracts prepared from young and old rats. Acetic acid extracts were prepared and subsequently fractionated by gel permeation chromatography. The high (> 10,000 daltons) and low (≤ 10,000 daltons) molecular weight fractions were collected, lyophilized and assayed. Radioimmunoassay competitive binding curves of the initial and fractionated extracts were parallel (p > 0.05) to the synthetic ANP 101–126 standard. No differences in parallelism (p > 0.05) were observed in the natriuretic activity of the initial extracts, the low molecular weight (LMW) fractions from both age groups, the 290 day high molecular weight (HMW) fraction or the synthetic ANP standard. However, the natriuretic activity of the 15 day HMW fraction was significantly attenuated compared to the other treatment groups (p