Rat atrial natriuretic polypeptide increases net water, sodium and chloride absorption across rat small intestine in vivo.

Localization of binding sites for synthetic rat atrial natriuretic polypeptide (alpha-rANP) and the effect of the peptide on net water and electrolyte movement in vivo perfused small intestine of the rat were studied. Autoradiographic study demonstrated that specific binding sites were localized on a space between the base of epithelia and lamina propria of the small intestine. Alpha-rANP (0.25 micrograms/min) infused into the superior mesenteric artery of rats increased net absorption of water (46% increase in comparison with controls), Na (84% increase) and Cl (70% increase) across the small intestinal tract perfused with Ringer's solution. These increases were also observed when glucose-free Ringer's solution was employed. Thus it would be concluded that the Na-glucose cotransport system is not involved in the action of alpha-rANP. These observations suggest that alpha-rANP controls circulating water-electrolyte balance through regulating not only renal function but also intestinal water, Na and Cl absorption.