Cell progression and radiosensitivity of T1-prospermatogonia in Wistar rats.

T1-prospermatogonia pass through a quiescent stage which lasts from before birth until day 4 after birth (p.n.). They progress into DNA synthesis and mitosis in two synchronous waves which are separated by 24 hours in the evenings of day 4 and 5. The first wave contains about 25 per cent of the total population, the second 75 per cent. The mean duration of S-phase is 10 hours, the mean duration of G2-phase is 4 hours. After irradiation, the capacity of T1-prospermatogonia to produce the normal number of proliferating and differentiating cells in the testes is reduced. During maturation, between day 21 post-conception (p.c.) and day 5 p.n. the radiosensitivity of T1-prospermatogonia decreases by a factor of over 5.