Extrinsic intestinal reinnervation after canine small bowel autotransplantation

The process of extrinsic reinnervation after small bowel transplantation is poorly understood.

Jejunal and ileal specimens, obtained from the dogs that underwent intestinal autotransplantation by an end-to end (E-E) or end-to-side arterial reconstruction, were analyzed at 1 (n = 7), 3 (n = 6), 6 (n = 6), 12 (n = 6), or 24 (n = 2) months and compared with control specimens (n = 7). Tissue catecholamine levels and indirect immunohistochemistry results for extrinsic neuropeptides, calcitonin gene-related peptide, neuropeptide Y, substance P, and tyrosine hydroxylase (TH) were examined.

Catecholamine levels in the grafts were undetectable until 6 months but increased significantly after 12 months, particularly in the E-E group. Immunohistochemistry results showed no significant indication of extrinsic reinnervation until 12 months, when TH fibers were observed in five of six dogs. The E-E group revealed some TH fibers extending across the arterial anastomosis toward the graft mesentery. Examination of the intestinal anastomosis at 12 months showed abundant peptidergic and TH extrinsic fibers in the host side, whereas there were few or none on the graft side.

These results suggest that extrinsic reinnervation of the graft intestinal wall does occur but requires a prolonged period, and the major route of extrinsic reinnervation is along the arterial axis of the intestinal graft, not beyond the enteric anastomosis.