INFLAMMATION CAUSES HYPERPLASIA AND HYPERTROPHY IN SMOOTH-MUSCLE OF RAT SMALL-INTESTINE

Inflammation of the rat jejunum with Trichinella spiralis causes altered smooth muscle contractility by day 6 postinfection (PI). We investigated the association of structural change in the smooth muscle layers with inflammation. By day 6 PI, smooth muscle area in cross sections of jejunum increased (P < 0.05) in longitudinal (LM) and circular (CM) muscle layers. Nuclei counting in cross sections showed that cell number increased two- to threefold in CM and LM, and this increase was not reversed on day 23 Pl. Estimation of cell size showed significant hypertrophy by day 6 PI in both muscle layers. [H-3]thymidine autoradiography showed that the labeling index (LI) of jejunal LM and CM increased sharply on day 4 PI and peaked on day 6 PI (10- to 15-fold increase). The noninflamed ileum showed a smaller trophic response, with no significant change in area or nuclei number; the LI was increased only on day 6 PI in the ileal CM and was unchanged in LM. Thus extensive hyperplasia and hypertrophy of smooth muscle cells are associated with intestinal inflammation.