EFFECT OF EXTENT OF RESECTION ON INTESTINAL MUSCLE ADAPTATION

The response of intestinal muscle to resection has received less atten tion than mucosal adaptation but may be important in relation to alter ed motility and improved intestinal absorption. Our aim was to determi ne the effect of extent of resection on intestinal muscle adaptation. Distal resections of 25% (n = 5), 50% (n = 5), and 75% (n = 5) of the intestine were performed, Transverse intestinal sections were taken at resection and 12 weeks later to evaluate changes in mucosa and circul ar and longitudinal muscle thickness. Muscle cell number and size and muscle length were also measured, Mucosal thickness increased (P < 0.0 5) after all resections, (1007 +/- 253 mu m vs 1259 +/- 181 mu m, 25%; 1019 +/- 191 mu m vs 1366 +/- 293 mu m, 50%; and 927 +/- 88 mu m vs 1 432 +/- 213 mu m, 75%). Longitudinal muscle thickness (169 +/- 35 mu m vs 254 +/- 45 mu m 50%; 207 +/- 71 mu m vs 353 +/- 103 mu m, 75%) and length (180 +/- 10 cm vs 203 +/- 16 cm, 50%; 90 +/- 16 cm vs 110 +/- 21 cm, 75%) increased (P < 0.05) following 50% and 75% resections but not after a 25% resection. Circular muscle length increased after 75% resection alone (4.4 +/- 0.2 cm vs 5.8 +/- 0.4 cm, P < 0.05). There wa s no significant change in circular muscle thickness after any resecti on. Muscle cell size and number per unit area were unchanged in all gr oups, We concluded that: (1) Intestinal muscle adapts after intestinal resection and this response is related to the extent of resection; in contrast, mucosal adaptation was evident following even the least ext ensive resection. (2) Increased thickness and length of the longitudin al muscle layer are the most prominent changes. (3) This increased mus cle thickness results from hyperplasia rather than hypertrophy. (C) 19 96 Academic Press, Inc.