Actomyosin, collagen, and cell hypertrophy in intestinal muscle after jejunoileal bypass

Previous observations indicate that bypass of 70% of the small bowel of rats induces increases in the seromuscular mass of both the in-continuity and the bypassed segment. The purpose of this study was to quantify the amount of actomyosin and collagen in the muscle layer and to determine the number of cells per cross-sectional area of the circular muscle layer at various locations of the small intestine after jejunoileal bypass. The amount of actomyosin relative to total tissue protein remained the same in the hypertrophied tissues compared with controls, and the actin-to-myosin ratios were similar. The collagen content per wet weight of the tissue from the sham- and bypass-operated animals tended to be less than in tissue from unoperated controls and was significantly less at the distal in-continuity location. The number of cells per cross-sectional area was decreased in tissues from all locations of the bypassed animals. These findings support the hypothesis that the increase in seromuscular mass after intestinal bypass is due to an increase in functioning smooth muscle tissue and that at least part of the increase is due to cell hypertrophy.