Influence of right atrial stretch and atrial natriuretic factor on rat intestinal fluid content.

1. Studies were made on the effects of right atrial stretch and atrial natriuretic factor (ANF) infusion on fluid movement into the intestinal tract. 2. Stimulation of the atrial volume receptors by inflation of an intracardiac balloon in the conscious, unrestrained rat did not change intestinal fluid content under normovolaemic conditions. 3. When the rat was rendered hypovolaemic by peritoneal dialysis (34% deficit in extracellular fluid volume), right atrial stretch significantly increased intestinal fluid content. Under these conditions, inflation of the balloon restored large intestinal fluid content to the pre-dialysis state, i.e. right atrial stretch completely abolished that component of fluid absorption attributable to the extracellular fluid volume deficit. 4. These data suggest that stimulation of the right atrial receptors inhibits intestinal fluid reabsorption but probably does not initiate fluid secretion. 5. There was no evidence that this might be mediated by ANF since rat ANF (twenty-eight residue peptide, Ser-99-Tyr-126), infused for 1 h at doses of 0, 0.05, 0.1 and 0.5 microgram/min, did not cause any detectable changes in the fluid content of the large or small intestine of similarly prepared hypovolaemic rats.