Observations on the gubernaculum during descent of the testis.

The mechanisms that influence the descent of the testis are not clearly understood. The gubernaculum is a structure worthy of scrutiny inasmuch as it is conspicuous during descent, but virtually disappears after descent is complete. Early in gestation, the rat gubernacular bulb consists of loose mesenchymal cells that develop into fibrillar cells. These later thicken into rhabdomyoblasts that, near the end of gestation, differentiate into spiral striated muscle bundles, and eventually migrate outward into the abdominal/scrotal wall. The rhabdomyoblasts of the female gubernaculum do not differentiate further but rather undergo fatty degeneration. It is possible that spiral contractions of the attached gubernaculum produce tension on the testis and induce descent. The gubernaculum as the receptor organ for testicular descent may be responsive to local testicular hormones. Likely candidates are testosterone, dihydrotestosterone, or Mullerian Inhibiting Substance. A thorough knowledge of the sequential differentiation of the gubernaculum during embryonic development sets the stage for the study of its response to hormonal manipulation both in vivo and in vitro.