Control of intestinal absorption by the renin-angiotensin system.

In vivo angiotensin II (ANG II) exerts a dose-dependent dual action upon intestinal absorption. At low doses, ANG II stimulates sodium (Na) and water absorption from all intestinal areas. At high doses, ANG II inhibits absorption. The stimulation of jejunal absorption in response to ANG II is secondary to the release of norepinephrine (NE) from enteric sympathetic nerves. ANG II may act either within the brain or at the sympathetic nerve terminal to liberate NE. In contrast, the inhibition of absorption in response to ANG II is due to enteric prostaglandin production. At the present time it is unclear whether the changes in absorption in response to ANG II in vivo are due to changes in transport processes or secondary to alterations in enteric hemodynamics. ANG II also exerts a dose-dependent dual action on intestinal ion and water absorption in vitro. The mechanisms responsible for changes in absorption in vitro are unknown. However, since enteric sympathetic nerves are severed from their ganglia, it is unlikely that ANG II stimulates absorption in isolated preparations through release of NE. ANG II exerts a major control over intestinal absorption following volume depletion. The hormone controls colonic absorption through release of aldosterone and directly influences jejunal absorption via enteric sympathetic nerves. ANG II may control ileal absorption following volume depletion. All components of the renin-angiotensin system are present within the intestine. Furthermore, ANG II-like immunoreactivity is present within enteric nerves. The role of locally formed ANG II in the control of intestinal absorption has not been studied. Models illustrating the effect of ANG II on intestinal absorption are discussed.