Myofibroblasts in the mucosal layer of the uterine tube.

Uterine tubes from cow, sheep, horse, pig, dog, cat, rabbit, and guinea pig were examined immunohistochemically for presence and distribution of contractile cells in the mucosal lamina propria. We tested for the presence of alpha-smooth muscle actin, tropomyosin, desmin, smooth muscle myosin (heavy chain) and cytoskeletal proteins vimentin and cytokeratin. Immunostaining for alpha-smooth muscle actin showed two distribution patterns: either positive cells were freely dispersed in the mucosal lamina propria or a distinct subepithelial layer of positive cells was seen. The first distribution pattern was found in the isthmic uterine tube segments of all animals examined. Alpha-smooth muscle actin was colocalized with tropomyosin (all species), desmin (horse, sheep), and smooth muscle myosin (sheep, cow). All these cells were found reactive with anti-vimentin but not with anticytokeratin and therefore were classified as myofibroblasts. A distinct subepithelial layer of alpha-actin and tropomyosin positive cells was seen in horse fimbriae. In other examined species alpha-smooth muscle actin immunoreactivity in the subepithelial region was very weak. Contractile cells in the uterine tube mucosa were supposed to influence mucosal condition and motility, and therefore to play a role in gamete transport.