Distribution of small intestinal lesions in anaphylaxis of rats

Hemorrhage and congestion were not uniformly distributed along the small intestine during systemic anaphylaxis in rats. Duodenum had little hemorrhage and congestion and the terminal ileum had even less. Maximum involvement occurred in jejunum of 13% of rats, in ileum of 47%, and in both jejunum and ileum of 40%. Sequential scoring along the entire length of small intestine revealed different patterns of distribution with more than one peak of intensity in some of the rats. Within a lesioned area, banding was common except where hemorrhage and congestion were so severe as to obliterate all patterns. Banding represented a gradient of injury with respect to the vascular supply. The pale stripes (less severe hemorrhage) contained the penetrating vessels derived from the terminal mesenteric arcades. The dark stripes (more severe hemorrhage) did not contain such vessels. In addition, the mesenteric side of the intestine was less affected than the antimesenteric side. This constituted a second gradient that might also be related to the distance from the vascular supply. In both instances, proximity to larger blood vessels had a protective effect. These two gradients and the variable sites and patterns of distribution have not been described previously in intestinal anaphylaxis. Gradients and the variability of the distribution of lesions in intestinal anaphylaxis should be considered in experiments on pathogenesis and altered function.