Effects of atrial natriuretic peptide (ANP) on jejunal net fluid absorption in the rat

The role of atrial natriuretic peptide (ANP) on jejunal net fluid transport was studied in intact rats as well as in rats subjected to a perivascular denervation of the intestinal segment. In rats with intact nerves, an acute volume expansion with 5% albumin (10% of estimated blood volume) decreased jejunal net fluid absorption by approximately 70% compared to control animals not subjected to volume expansion. After a perivascular denervation of the intestinal segment, the acute volume expansion reversed net fluid absorption into a net fluid secretion. In order to reduce the volume expansion-induced endogenous release of ANP, one group of rats was subjected to a right atrial appendectomy 7 days prior to the experiments. In these animals, the intestinal response to the same 10% volume load was blunted compared to controls. Administration of rat alpha-ANP (99-126; 5 micrograms kg-1 i.v.) induced effects similar to those of volume expansion both in rats with intact perivascular nerves as well as in denervated animals. Volume expansion increased mean arterial pressure (MAP) as well as central venous pressure and decreased heart rate (HR) in all groups. When exogenous ANP was administered, a fall in MAP was seen, while HR remained unchanged. In conclusion, these data strongly indicate a physiological role for ANP in jejunal fluid transfer in response to acute volume expansion.