Natriuretic factor in rats acutely expanded by Ringer's versus albumin solution.

Previous studies have shown that it is possible to extract a natriuretic factor from the renal tissue of rats. This substance, which can be isolated by fractionation through a G-25 Sephadex column, shows a strong correlation with sodium elimination by the kidney. The present work was designed to compare the effects of expansion by a Ringer's solution versus an albumin solution on the presence of this factor and the natriuretic response in the rat. Albumin-expanded rats, like control nonexpanded rats, which have no natriuretic response, do not exhibit any active natriuretic factor in their kidneys. In contrast, significant activity of the natriuretic factor is found in the kidneys of Ringer-expanded rats, which also respond by a significant natriuresis (P less than 0.001). We conclude that the expansion of the extracellular fluid volume, as opposed to the expansion of the intravascular volume, only determines both the presence of the natriuretic factor and the physiologic natriuretic response. As the difference in the sodium transport by the renal tubule in these two modes of expansion takes place in the collecting duct, we suggest that the natriuretic factor acts at this level.