Gonadotrophin-induced reinitiation of meiosis in testes of oestradiol-treated prepubertal rats.

Male rats injected with 50 micrograms oestradiol dipropionate every 5 days from birth were given daily injections of 20 i.u. PMSG from 20 to 29 days of age. Testicular weight and cell number remained relatively constant in rats treated only with oestradiol and were significantly below normal levels, but significantly increased in PMSG-treated animals. Dissociated cells from PMSG-treated rats incorported 560% as much [3H]thymidine as did cells from oestradiol-treated animals at 21 days, and 240% at 29 days. The increase was due to new cells entering the S-phase, as indicated by an increase in the labelling index. Autoradiographic examination of testicular tissue indicated that PMSG stimulated DNA synthesis in meiotic and somatic cells. The number of labelled germinal cells increased and numerous pachytene spermatocytes were observed after 6--9 days of treatment. Myoid and interstitial cells were markedly stimulated by PMSG. The presence of spermatids in 26- and 29-day-old PMSG-treated animals indicated recue of pachytene spermatocytes destined to degenerate after oestradiol administration. It is concluded that the hormonal control of the meiotic process is similar in prepubertal and adult rats.