Muscarinic cholinergic receptor density following small intestinal transplantation in rats

After small intestinal transplantation, intestinal isografts can organize migrating myoelectric complexes, and we have shown that migrating myoelectric complex frequency in the fasted state was reduced compared with controls after transplantation of the distal 50% of small intestine. We hypothesized that changes in motor activity after transplantation were related to alteration of cholinergic nerve activity or receptor density. With use of standard microsurgical techniques, the distal 50% of small intestine was orthotopically transplanted in a Lewis-to-Lewis donor-recipient combination. Resection controls were prepared by resecting the proximal 50% of small intestine, and sham controls were prepared by performing a sham laparotomy. Two months after surgery, small intestine was harvested. Choline acetyltransferase activity among the three groups was similar, suggesting that intrinsic cholinergic nerves remained intact. There was a strong trend toward decreased acetylcholinesterase activity [analysis of variance (ANOVA), P = 0.16] after transplantation, consistent with loss of extrinsic vagal nerve fibers. There were no differences in histochemical distribution of acetylcholinesterase among these groups. Muscarinic receptor density, as determined by binding to [N-methyl-3H]scopolamine, was decreased after transplantation (ANOVA, P = 0.02). There was a trend toward decreased receptor density in animals with resected small intestine. Surgical interruption of intrinsic nerve pathways rather than ischemia or extrinsic denervation might be the mechanism for diminished receptor density after transplantation, and reduced small bowel motor activity may be related to decreased density of muscarinic cholinergic receptors.