An oxytocin-like peptide is present in the interstitial cells of the testis, and testicular concentrations of oxytocin have been shown to increase seminiferous tubule movements in vitro. We have used the drug ethan-1,2-dimethanesulphonate (EDS), which depletes the Leydig cell population of the adult rat testis, to examine further the relationships between the Leydig cell, testicular oxytocin and tubular movements. Adult rats were injected i.p. with a single dose of EDS (75 mg/kg) or of vehicle (25% dimethyl sulphoxide). Histological study 3 and 10 days after treatment with EDS showed a reduction in the number of interstitial cells, and levels of oxytocin immunoreactivity were undetectable by radioimmunoassay. Immunostaining revealed very few oxytocin-reactive cells. Spontaneous contractile activity of the seminiferous tubules in vitro was also dramatically reduced, but could be restored by the addition of oxytocin to the medium. Four weeks after EDS treatment, the interstitial cells were similar to those in the control animals both in number and in immunostaining; immunoassayable oxytocin was present and tubular movements were normal. The EDS effect, seen at 3 and 10 days, was not altered by daily treatment with testosterone. However, repopulation of the testes with oxytocin-immunoreactive cells was not seen until 6 weeks in the testosterone-treated animals.
We suggest that the Leydig cells are the main source of oxytocin immunoreactivity in the testis and that this oxytocin is involved in modulating seminiferous tubule movements and the resultant sperm transport. The results also imply that testosterone does not play a major role in controlling tubular activity in the mature rat.