Actions of centrally administered neuropeptides on rat intestinal transport: enhancement of ileal absorption by angiotensin II

Recent evidence suggests that opioids and other peptides may act within the CNS to modulate intestinal fluid and ion transport. In this study, the brain peptides bombesin and angiotensin II were examined for their ability to alter water flux across the small intestine after their intracerebroventricular (i.c.v.) administration to rats. In addition, changes in mean arterial pressure and respiratory frequency were determined after peptide treatment to assess the physiological specificity of their CNS actions. Bombesin, administered by i.c.v. bolus injections (10-1000 ng/rat) or continuous infusion (100 ng/min), rapidly elevated blood pressure and respiration, but had no significant effect on water transport in proximal jejunum or distal ileum in situ (as measured by single-pass perfusion with [¹⁴C]polyethylene glycol as non-absorbed water marker). Angiotensin II rapidly increased blood pressure and enhanced ileal absorption 30 min after its i.c.v. bolus injection at 0.1-1 μg, but had no effect on jejunal transport or respiration. These effects were inhibited in rats pretreated with either the angiotensin antagonist [Sar¹, Val⁵, Ala⁸]angiotensin II (5 μg i.c.v.) or the α-adrenoceptor antagonist, phentolamine (1 mg/kg i.v.). In contrast, atropine methylnitrate (0.1 mg/kg i.v.) pretreatment inhibited the proabsorptive, but not the pressor effects of angiotensin. These results indicate for the first time that angiotensin II promotes fluid absorption in the rat intestine by an action within the CNS. The mechanisms underlying this novel action of angiotensin appear to differ from those responsible for its hypertensive action.