Peritubular Contractile Cells in Testis and Epididymis of the Dog, Canis lupus familiaris

Contractile cells surrounding the tubular system of the mammalian testis and epididymis are supposed to contribute to the initial transport of spermatozoa from the testis to epididymis. Testicular peritubular smooth muscle cells have been characterised in detail especially in rodents and humans. The aim of our study was to assess the distribution of peritubular contractile cells of the canine tubuli seminiferi, rete testis channels, ductuli efferentes, and ductus epididymidis by immunohistochemistry and transmission electron microscopy and to classify these cells with respect to their possible physiological function. The entire tubular system of the canine testis and epididymis is surrounded by contractile cells expressing smooth muscle actin, smooth muscle myosin and desmin, which are enveloped, at least partly, by a basal lamina. Some contractile cells of the tubuli seminiferi, rete channels, and efferent ducts and sometimes also single peritubular cells of the ductus epididymidis express vimentin. Contractile cells of seminiferous tubules and efferent ducts represent an intermediate cell type exhibiting characteristics of both smooth muscle cells (SMC) and myofibroblasts, those of rete channels stellate myofibroblasts, and those of the ductus epididymidis SMC. Differences in structure and arrangement of the contractile cells between seminiferous tubules, rete channels, efferent ducts, and ductus epididymidis suggest different functions. Myofibroblasts and contractile cells similar to them could be mainly responsible for the maintenance of an appropriate tissue turgor, whereas contraction of SMC of the ductus epididymidis might cause propulsion of spermatozoa by peristaltic waves.