The occurrence of unusual smooth muscle bundles expressing alpha-smooth muscle actin in human intestinal atresia

Abstract

Background/purpose: Intestinal dysmotility is an important problem in the postoperative management of patients with intestinal atresia (IA). Changes in the intramural components have so far been histochemically and immunohistochemically examined in both the proximal and distal segments of IA, but no detailed analysis of the muscular elements has been performed. The aim of this study was to carefully examine any alterations in the muscular elements in the intestines from patients with IA.

Methods: Resected intestines were obtained from 6 patients with ileal atresia, 4 patients with jejunal atresia, and 3 controls without gastrointestinal diseases obtained by autopsy (congenital diaphragmatic hernia). All specimens were immunochemically stained with a monoclonal antibody to alpha-smooth muscle actin (alpha-SMA) as a smooth muscle marker.

Results: In the normal small intestine, almost all the enteric smooth musculature were positive for alpha-SMA antiserum, except for the bulk of the circular musculature. In the proximal segments of all cases with IA, a reduced staining intensity for alpha-SMA was observed mainly in the severely hypertrophic muscle layers. In addition, some bundles of smooth muscle also were located in the submucosal connective tissue near the border of the innermost layer of the circular musculature, in which large amounts of smooth muscle fibers extended occasionally from the innermost layer of the circular musculature to the muscularis mucosae in the proximal segments of 4 cases. In the distal segments of IA, the distribution of alpha-SMA-positive smooth muscle fibers was similar to that in the control intestines, excluding mild to moderate hypertrophy of the muscular layers.

Conclusions: Both severe hypertrophy and a reduced immunoreactivity for alpha-SMA were observed in the circular muscle layer of the proximal segments. In addition, the occurrence of alpha-SMA-positive abnormal smooth muscle fibers was recognized in the submucosal layers of the proximal segments, thus, suggesting a delay in the intestinal muscular formation or a regressive reaction secondary to dilatation. These muscular alterations in the proximal segments might be considered to contribute to the postoperative intestinal dysmotility in IA cases.