Early mucosal healing and chronic changes in pony jejunum after various types of strangulation obstruction

SUMMARY Strangulation obstruction was induced in anesthetized ponies for periods of 2 and 3 hours by clamping 45-cm segments of jejunum and their veins only (venous strangulation obstruction, vso) and arteries and veins (arterial and venous strangulation obstruction, avso). These types of strangulation obstruction were studied in 4 segments in each of 4 ponies allowed to survive 12 hours (group 1) and in a single segment in each of 10 ponies allowed to survive 42 days (group 2) after the strangulation period ended. On visual inspection, segments subjected to vso had hemorrhage and edema in the bowel wall and mesentery and were dark purple after all time intervals. They improved slowly after clamps were removed, but remained hemorrhagic and edematous. Segments subjected to avso were purple and had mild edema and scattered petechiae in the bowel wall and mesentery. They improved rapidly and closely resembled normal bowel after 5 minutes of reperfusion. On light and scanning electron microscopy, the mucosa of intestine subjected to vso and avso had necrotic, denuded villi 1 hour after the strangulation periods ended. Twelve hours after removal of occlusion devices in group-1 ponies, 4 (25%) segments were unchanged, 4 (25%) had deteriorated, and 8 (50%) had stunted villus remnants partly or completely lined with regenerating epithelium. Separation and detachment of villus tip mucosal cells were seen in 3 of 4 control segments, 1 and 12 hours after the strangulation periods ended. At necropsy, all ponies in group 2 had normal test segments, except for 1 that had stricture at a previous clamp site. In 2 ponies that had segments subjected to 3 hours of vso, the mesentery was short and thick between the points where vascular clamps had been applied. These findings suggest that brief periods of strangulation obstruction can induce severe gross changes in the intestinal wall, but that necrosis can be limited to the villus tip cells in the strangulated segment and, to a lesser degree, in nonstrangulated segments of jejunum. Mucosal repair was characterized by reepithelialization of stunted villi at 12 hours after the ischemic injury and these villi acquired normal length and architecture some time later. The rare long-term effects of ischemia were largely confined to the mesentery and were attributed to the effects of hemorrhage and edema.