Role of the natriuretic hormone in the specific natriuresis induced by intraportal infusion of hypertonic saline in dogs

: Previous experiments from our laboratory demonstrated that the infusion of a small amount of hypertonic saline into the portal vein induced higher diuresis and natriuresis than those induced by the infusion of the same amount of saline into a cubital vein. The purpose of the present experiment was to study the role of the so-called natriuretic hormone in this phenomenon. For this purpose, two groups of 5 dogs each were infused with 855 mM NaCl (0.05 ml X min-1 for 20 min), one group through the portal vein and the other through the cubital vein. Samples of peripheral, arterial and suprahepatic blood and urine were obtained, and the fraction described to contain the natriuretic hormone was purified by gel filtration chromatography. Its natriuretic activity was assayed by measuring the natriuresis induced by its infusion in conscious, unilaterally nephrectomized rats. The urine taken from the dogs infused with hypertonic saline into the porta showed higher natriuretic activity than that obtained before infusion or from the dogs infused into the cubital vein. Also, natriuretic activity was observed in the suprahepatic and arterial plasma samples obtained after portal infusion but not in those obtained before the infusion. There were no differences in natriuretic activity between suprahepatic and arterial samples. These results suggest that the natriuretic hormone plays an important role in the natriuresis induced by portal hypertonic saline infusion, and they do not support the hepatic origin of this substance.