Undernourishment and Yersinia enterocolitica Enterocolitis Alter Intestinal Contractility in the Rabbit: Role of Smooth Muscle Contractile Protein Content

Previous studies have demonstrated that the longitudinal smooth muscle of rabbits infected with Yersinia enterocolitica and undernourished because of reduced food intake exhibit a significantly reduced ability to develop tension in response to carbachol compared with pair-fed animals, which are uninfected but equivalently undernourished. To determine whether the alteration in smooth muscle contractility results from changes in cell number (hypo- or hyperplasia), or in contractile protein content or isoform distribution, New Zealand White rabbits (600 to 1000 g) were randomly assigned to one of three treatment groups: infected, pair-fed or control. Tissue contractility was measured, morphometric studies were performed and immunoassays were developed for the measurement of total actin, gamma-enteric and alpha-vascular isoactins, and myosin heavy chain. Consistent with what was found in previous reports, the contractility of longitudinal smooth muscle in response to carbachol was found to increase in pair-fed animals and to decrease in Y enterocolitica-infected animals. There was no significant change in the proportional thickness of the ileal longitudinal smooth muscle coat, and the number of cross-sectioned longitudinal smooth muscle cells/mm2 was not significantly different in infected, pair-fed or control tissues. Immunoassay indicated that the proportion of each specific contractile protein, relative to total protein content in the muscularis propria, was unaffected by Y enterocolitica infection or by pair-feeding. Thus, the alterations in intestinal longitudinal smooth muscle function observed after Y enterocolitica infection were concluded not to be associated with tissue hypo- or hyperplasia, or changes in the total content or isoform distribution of contractile proteins in the muscularis propria.