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 r abbits infected with Yersinia enterocolitica and undernourished because of reduced food intake exhibit a significantly reduced ability to develop tens ion in response to carbachol compared with pair-fed animals, which are unin fected 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 contractilit y was measured, morphometric studies were performed and immunoassays were d eveloped for the measurement of total actin, gamma-enteric and alpha-vascul ar isoactins, and myosin heavy chain. Consistent with what was found in pre vious 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 pr oportional thickness of the ileal longitudinal smooth muscle coat, and the number of cross-sectioned longitudinal smooth muscle cells/mm(2) was not si gnificantly different in infected, pair-fed or control tissues. Immunoassay indicated that the proportion of each specific contractile protein, relati ve to total protein content in the muscularis propria, was unaffected by Y enterocolitica infection or by pair-feeding. Thus, the alterations in intes tinal longitudinal smooth muscle function observed after Y enterocolitica i nfection were concluded not to be associated with tissue hypo- or hyperplas ia, or changes in the total content or isoform distribution of contractile proteins in the muscularis propria.