Morphological and immunohistochemical changes in intestinal mucosa and PYY release following total colectomy with ileal pouch-anal anastomosis in dogs.

Other studies have shown that both morphological and functional adaptation occur in the ileal mucosa after total colectomy and may be mediated by humoral factors. To elucidate the participation of peptide YY (PYY) in intestinal adaptation after total proctocolectomy with ileal pouch-anal anastomosis (IPAA), changes in the number of PYY-containing cells and in histological appearance in the intestinal mucosa, especially in the mucosa of ileal pouch, were investigated in dogs. We further examined changes in postprandial PYY release in relation to those in PYY-containing cells. Ten adult beagle dogs underwent IPAA. Before and 2, 6, and 12 months after surgery, a test meal was given, and blood samples were taken from a foreleg vein at intervals for 3 hr for measurements of plasma PYY concentration by radioimmunoassay. Before and one year after surgery, morphological studies of the intestinal mucosa were performed using parameters such as villous height (VH), mucosal thickness (MT), and villous index (VI). Immunohistochemical studies of PYY were also done in the intestinal mucosa. Both fasting and postprandial plasma PYY levels were reduced to half of the preoperative levels at two months after surgery. Thereafter, postprandial levels approached preoperative concentrations, while fasting levels remained unchanged. VH, MT, and VI were significantly smaller in the ileal pouch than in the ileal end of the controls. The MT of the ileal pouch was similar to that of the colon. PYY-containing cells in the mucosa of the ileal pouch were distributed more densely than those in the ileal end, similar to those in the colon of the controls. It was concluded that after IPAA, the pouch mucosa gradually changed to resemble the colonic mucosa not only in histological appearance but also in the population of PYY-containing cells. It is therefore considered that colonic transformation of the ileal-pouch mucosa is closely related to the increase in the number of PYY-containing cells and the steady recovery of postprandial PYY secretion.