Oxytocin in Leydig cells: an immunocytochemical study of Percoll-purified cells from rat testes

Testicular interstitial cells, from rats aged 35 days, were dispersed with collagenase and separated through Percoll into 5 fractions (I-V); fraction I being the least dense. Measurement of basal testosterone production, histo-enzymological staining for 3 beta-hydroxysteroid dehydrogenase activity and electron microscopy indicated that the majority of Leydig cells were found in fraction IV (corresponding to a density of 1.076-1.097 g/ml). In addition, cells from this fraction responded to hCG treatment in a dose-dependent manner on day 0 and remained responsive after being cultured for 1 day. Immunostaining for oxytocin indicated that this fraction also contained the majority of the oxytocin-immunoreactive cells. On day 1 of culture, 56% of the cell population from fraction IV were positively stained for the steroidogenic enzyme and 75% immunoreactive for oxytocin. This overlap indicates that the Leydig cells were also the oxytocin immunoreactive cells.