Testicular germ cell differentiation in vivo.

The effects of artificial cryptorchidism and surgical reversal on spermatogenesis were examined in mice. Only undifferentiated type A spermatogonia were present as germ cells in cryptorchid testes. The surgical reversal of cryptorchidism resulted in regenerative differentiation of mature germ cells as judged by testicular weight, histologic examination, and increase in the specific activity of lactate dehydrogenase-X. Leydig cell function was also examined by assessment of the weight of target tissues of androgen. They showed a unique change following the surgical reversal. Thirty days after surgical reversal, hyperfunction of the Leydig cells was observed, and the testes became normal after 60 days.