Cholinergic Agents Modulate Transport in the Isolated, Perfused Ileum

Abstract

The mammalian small intestine is extensively innervated by cholinergic nerve fibers, including projections to the muscular and submucosal layers. This study tested the hypothesis that cholinergic agents modulate ileal transport independent of alterations in intestinal vascular resistance and motility. Ten-centimeter segments of rabbit ileum ( n = 32) were vascularly perfused ex vivo with a physiologic electrolyte solution containing red cells. The lumen was perfused with an electrolyte solution containing [ 14C]polyethylene glycol. Net fluxes of water, sodium, and chloride were calculated during three 20-min periods: basal, drug infusion, and recovery. Agents infused at a final arterial concentration of 10 -5 mole/liter included acetylcholine, atropine, and hexamethonium. Measured perfusion pressure reflected changes in vascular resistance. Recovery calculations controlled for motility effects. Acetylcholine caused significant secretion of water, sodium, and chloride ( P < 0.05). The infusion of atropine or hexamethonium alone had no effect. Atropine but not hexamethonium prevented the prosecretory effect of acetylcholine. There were no significant changes in perfusion pressure or 14C recovery for any infused agent. Acetylcholine-induced ileal secretion is (1) mediated via atropine-sensitive muscarinic cholinergic receptors, (2) independent of extraintestinal neural pathways, and (3) independent of changes in vascular resistance or motility. These data support the hypothesis that acetylcholine influences ileal transport directly, independent of alterations in vascular resistance and motility.