Testicular migration: remodeling of connective tissue and muscle cells in human gubernaculum testis.

PURPOSE: We present the main morphological modifications in the human gubernaculum during testicular migration in humans.
MATERIALS AND METHODS: We obtained 12 gubernacula from fresh, macroscopically normal human fetuses at 15 to 29 weeks of gestation. Collagen was evidenced using trichrome and Sirius red staining procedures, while Weigert's resorcinol-fuchsin and anti-human elastin antibody were used to reveal elastic system fibers. Smooth muscle cells were detected by anti-human smooth muscle alpha-actin antibody.
RESULTS: When the testes were still located in the abdomen at 15 to 16 weeks of gestation, collagen fibers were sparse and embedded in a loose extracellular matrix. The amount of fibers then gradually increased with age and at 28 weeks of gestation the gubernaculum was mostly collagenous in composition. Elastic fibers had a similar growth pattern, although they were located mainly at the distal end of the gubernaculum. Fibroblasts largely predominated over other cell types and decreased in number with gestational age, whereas smooth muscle cells were restricted to the walls of blood vessels. Striated muscle cells were detected at the scrotal end of the gubernaculum, where they were disposed as isolated and scattered bundles running in various directions. Like fibroblasts, their number also decreased with age.
CONCLUSIONS: During testicular migration gubernacular connective tissue undergoes extensive remodeling and ultimately becomes an essentially fibrous structure rich in collagen and elastic fibers. Such changes should decrease the size of the gubernaculum and, thus, contribute to other forces that cause the testes to move toward the scrotum. In fact, because of the lack of smooth muscle cells, and the amount and organization of striated muscle cells, active contraction of the gubernaculum is less likely to be an important factor in testicular descent.