Increased release of atrial natriuretic peptide by the atria of rats with experimental renal failure.

Indirect evidence suggests that atrial natriuretic peptide (ANP) secretion is augmented in chronic renal disease. The object of our present study is to examine the release of ANP from isolated atria obtained from chronic renal failure rats to directly determine whether ANP secretions are increased under these conditions. Experiments were conducted on male Wistar rats (200-225 g) who were subjected to 5/6 nephrectomy of sham operation. Plasma blood urea nitrogen was significantly elevated in 5/6 nephrectomized rats (65 +/- 7 vs. 16 +/- 1 mg%). Overall glomerular filtration rate was 2.36 +/- 0.06 ml/min in sham-operated animals, as opposed to 0.55 +/- 0.11 ml/min in 5/6 nephrectomized rats. Fractional excretion of sodium was significantly higher in 5/6 nephrectomized rats (0.52 +/- 0.01 vs. 1.68 +/- 0.21%). Plasma ANP was 102 +/- 4 pg/ml in normal rats and 161 +/- 14 pg/ml in 5/6 nephrectomized ones. We have also measured immunoreactive ANP in the atria of normal and 5/6 nephrectomized rats. ANP content and concentration in the atria were lower in 5/6 nephrectomized rats. (652 +/- 34 vs. 515 +/- 46 ng/mg of tissue). Right atria from normal and nephrectomized animals was superfused with a modified Langendorff preparation. Spontaneous release of ANP was significantly higher from the nephrectomized rats (17.5 +/- 0.6 pg/min/mg) than from the normal rats (9.8 +/- 0.3 pg/min/mg). These results suggest that ANP may play a role in sodium homeostasis in rats with reduced renal mass.