Functional changes in nonadrenergic, noncholinergic inhibitory neurons in ileal circular smooth muscle after small bowel transplantation in rats.

This experiment was designed to determine mechanisms of change in nonadrenergic, noncholinergic (NANC) inhibitory neurons in the ileum after small bowel transplantation (SBT) in the rat and whether nitric oxide (NO) serves as an important NANC inhibitory neurotransmitter in the rat ileum. Eight groups of rats (N > or =8 rats/group) were studied: neurally intact unoperated controls; rats one week after anesthesia and sham celiotomy; and separate groups one and eight weeks after either 40 min of cold ischemia of the jejunoileum, combined jejunal and ileal intestinal transection/reanastomosis, or orthotopic SBT of the entire jejunoileum. Contractile activity was evaluated in full-thickness ileal circular muscle strips under isometric conditions. Spontaneous activity did not differ among groups. In all groups, exogenous NO, NG-monomethyl-L-arginine (L-NMMA, an NO synthase inhibitor), and methylene blue (soluble guanylate cyclase inhibitor) had no effect on spontaneous activity, while 8-bromocyclic guanosine monophosphate (8Br-cGMP) inhibited contractile activity in all groups. Low frequency (2-10 Hz) electrical field stimulation (EFS) inhibited contractile activity only in control and SBT groups; L-NMMA and methylene blue did not alter the response to EFS in any group. These results suggest that each aspect of the SBT procedure, ischemia/reperfusion injury, disruption of enteric neural continuity by intestinal transection, and extrinsic denervation, alter function of enteric ileal inhibitory neurons separately early (one week) after operation. NO, a known inhibitory neurotransmitter in other gut regions, does not affect ileal circular muscle in neurally intact tissue nor mediate functional changes in inhibitory nerve function nor smooth muscle contractility after SBT.