Search

The value of mucosal biopsies in evaluating small bowel rejection is controversial. In this study, the value of mucosal biopsies was estimated in unmodified porcine small bowel rejection. Ten animals received the distal half of the small bowel as a heterotopic loop (Thiry-Vella loop). The allografts were followed by proximally and distally harvested full-thickness and mucosal biopsies every other day, starting from the 3rd day and continuing until the grafts became necrotic. The histological parameters in both types of biopsies were semiquantitatively scored from 0 to 3 and compared with each other. The difference in mean values on the subsequent days was not remarkable, the results favoring slightly higher values in full-thickness than in mucosal biopsies. Our results suggest that multiple mucosal biopsies are adequate in monitoring morphological changes of small bowel grafts during rejection and that the proximal and distal ileum are similarly affected by acute rejection.

Cholesterol absorption occurs primarily in the upper small intestine. Our aim was to assess absorption of cholesterol during ileal adaptation after proximal small intestinal resection. In vivo absorption and elimination of cholesterol, plasma cholesterol, cholesterol precursors, and plant sterols were related to intestinal morphology and transit 4 (n = 5), 8 (n = 5), and 14 (n = 5) weeks after a 75% proximal resection of porcine small intestine, and compared to preoperative (n = 5) and transected (n = 5) control animals. Fractional cholesterol absorption, the daily amount of cholesterol absorbed, plasma cholesterol, and plant sterol to cholesterol proportions were significantly (P < 0.05 or less) decreased, whereas fecal loss of cholesterol as neutral steroids, less so as bile acids, plasma cholesterol precursor proportions, and ileal mass and villus height were significantly increased (P < 0.05 or less) after 8 weeks of the resection. Cholesterol absorption efficiency, decreased by the resection, was gradually increased from 5.4 +/- 2.2 to 26.9 +/- 3.9% during the 14 postoperative weeks (P < 0.0001) simultaneously with a 46% increase in villus height compared with transection (P < 0.0001), but absorption remained still below control levels (80.4 +/- 2.5%, P < 0.0001). In resected and control animals, villus height correlated positively with cholesterol absorption efficiency (r = 0.85, P < 0.0001; r = 0.76, P = 0.01) and plasma plant sterol proportions (r = 0.94-0.95, P < 0.0001; r = 0.78-0.85, P < 0.008), respectively. In conclusion, after massive proximal small bowel resection, adaptation of intestinal cholesterol absorption efficiency occurs in the distal ileum closely parlleling villus hypertrophy.

Porcine small bowel allografts were followed for 18 weeks during immunosuppression with cyclosporine-A (CyA), azatioprine and prednisone. The mucosal alterations noted at the 12th week were epithelial vacuolation and loss of Goblet cells. Moderate infiltration of inflammatory cells, mainly lymphocytes, was found in the lamina propria. In addition, a few grafts exhibited oedema and fibrosis. Vessels already showed endothelial swelling and intimal proliferation at the 12th week. In the submucosa, the infiltration of inflammatory cells was not present till the 18th week. Further changes in the mucosa at the 18th week were the blunting of villi, cuboidal epithelium, crypt abscesses and epithelial atrophy. The histological alterations of mucosa and lamina propria existing in the full thickness biopsies were mostly also detectable in mucosal biopsies, provided that multiple biopsies were taken. Thus these parameters analyzed from mucosal biopsy material are suitable for the diagnosis and monitoring of chronic small bowel rejection. In autopsy, the most prominent features were in the mesenterial arteries: intimal proliferation, vasculitis, proliferation of media and endothelial alterations. The activity of the mucosal disaccharidases maltase and sucrase remained near the initial level till the 12th week and had decreased markedly by the 18th week.

Our major aim was to investigate the consequences of ileal autotransplantation in pigs with proximal small intestinal resection on biliary lipids and metabolism of bile acids. Biliary lipid secretion rates and bile acid absorption were assessed by measuring dietary and biliary lipids, fractional cholesterol absorption, and fecal excretion of cholesterol and bile acids. In addition, serum bile acids and cholesterol, biliary and fecal bile acid species, and ileal villus height were determined after resection of the proximal 75% of the jejunoileum (n = 15) and autotransplantation of the remaining ileum with systemic venous drainage (n = 15) or transection (n = 5). Autotransplantation further increased fecal excretion of neutral and acidic steroids and serum concentration of bile acids after proximal resection (P < .05 for all); autotransplantation significantly decreased serum cholesterol, ileal villus height, fractional bile acid and cholesterol absorption, and biliary molar percentage of total and primary bile acids, whereas biliary secretion of bile acids, enriched by secondary bile acids, and cholesterol remained unchanged. At 14 weeks, ileal villus height, fractional bile acid and cholesterol absorption, biliary molar percentage of bile acids, and proportion of secondary biliary bile acids were altered by transplantation from the respective postresection values of 864 +/- 22 microm, 97.9 +/- 0.6%, 26.9 +/- 3.9%, 91.8 +/- 1.2% and 9.2 +/- 1.3% to 428 +/- 21 microm, 91.1 +/- 1.5%, 9.5 +/- 1.1%, 83.9 +/- 1.4% and 52.5 +/- 3.5% (P < .005 for all). Posttransplantation biliary bile acid secretion correlated positively with fractional reabsorption (r = .70) and biliary molar percentage (r = .73) of bile acids and ileal villus height (r = .65; P < .01 for all). Decreased absorption efficiency and biliary molar percentage of bile acids, increased biliary secondary bile acids, and short ileal villi point to bacterial overgrowth-induced bile acid malabsorption, which with decreased absorptive area may contribute to malabsorption of other lipids after ileal autotransplantation. Compensatory increase in cholesterol synthesis in the pigs with autotransplanted ileum appeared sufficient for constant biliary secretion of cholesterol and bile acids.