Response of isolated rat jejunum to angiotensin peptides.

Following intravenous infusion, angiotensin I (ANG I), angiotensin II (ANG II), and angiotensin III (ANG III) enhance Na and water absorption across the jejunum by increasing sympathetic nerve activity. Increased absorption following intravenous infusion of angiotensin peptides may be secondary to an increase in ion transport. To test this hypothesis, the effect of angiotensin peptides on ion and water absorption from the isolated jejunum was studied. At a dose of 100 pM, serosal addition of ANG II stimulated jejunal Na and water absorption. In contrast, mucosal additions of the peptide were ineffective at doses up to 1 microM. ANG II enhanced jejunal absorption in the presence of prazosin. Thus ANG II does not appear to stimulate absorption from the isolated intestine through mediation of sympathetic fibers. ANG III and the substituted analogue [Sar1,Leu8]ANG II stimulated jejunal absorption at a dose of 100 pM. At a dose of 1 nM ANG I also stimulated jejunal absorption. The effect of ANG I on absorption could be prevented by prior treatment of the animals with the converting enzyme inhibitor MK 422. Thus ANG I must first be converted to ANG II to stimulate jejunal absorption.