MUSCARINIC CHOLINERGIC RECEPTOR DENSITY FOLLOWING SMALL-INTESTINAL TRANSPLANTATION IN RATS

After small intestinal transplantation, intestinal isografts can organ ize 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 intest ine. We hypothesized that changes in motor activity after transplantat ion were related to alteration of cholinergic nerve activity or recept or density. With use of standard microsurgical techniques, the distal 50% of small intestine was orthotopically transplanted in a Lewis-to-L ewis 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, sm all intestine was harvested. Choline acetyltransferase activity among the three groups was similar, suggesting that intrinsic cholinergic ne rves remained intact. There was a strong trend toward decreased acetyl cholinesterase activity [analysis of variance (ANOVA), P = 0.161 after transplantation, consistent with loss of extrinsic vagal nerve fibers . There were no differences in histochemical distribution of acetylcho linesterase among these groups. Muscarinic receptor density, as determ ined by binding to [N-methyl-H-3]scopolamine, was decreased after tran splantation (ANOVA, P = 0.02). There was a trend toward decreased rece ptor density in animals with resected small intestine. Surgical interr uption of intrinsic nerve pathways rather than ischemia or extrinsic d enervation might be the mechanism for diminished receptor density afte r transplantation, and reduced small bowel motor activity may be relat ed to decreased density of muscarinic cholinergic receptors.