Depletion of Mouse Spermatogonia following Exposure to Polonium-210

LOCALIZATION of polonium-210 ( 210 Po) in the interstitial spaces of the testes of rats has been demonstrated radio-autographically 1 and a very slow rate of excretion of 210 Po from rat testis has also been shown. 210 Po is a naturally occurring alpha-emitting element of the uranium decay chain. A particle energy of 5.3 MeV allows a range for the 210 Po alpha particle of about 37µ, in tissue. Since this distance is sufficient to penetrate from the interstitial spaces of the testis into the outer cell layers of the seminiferous tubules of the testis where spermatogenesis occurs, it seemed important to ascertain the effect of 210 Po on spermatogenesis. The survival of resting primary spermatocytes in stage VII tubules of mouse testis was measured by methods described by Oakberg in studies of the response of the mouse testis to external radiation exposure 3 and later used for the evaluation of tritiated thymidine toxicity 4 . Male Harvard Swiss Wistar mice 2–25 weeks of age were injected peritoneally with 0–2 nc. of 210 Po, obtained from the Radiochemical Centre, Amersham, and constituted in 0.05–0.25 ml. of isotonic weakly acid solution prepared by dilution with normal saline. At intervals from 5 days to 10 months after injection, mice were killed by cervical dislocation and their testes removed and fixed in either Bouin's solution or 10 per cent neutral formalin. The tissues were embedded in paraffin and cut into 5µ sections. Prepared slides were stained with periodic acid–Schiff–haematoxylin stains and examined at 1,000 × magnification using an oil immersion objective. Only seminiferous tubules cut in cross-sections so that they appeared round were selected for scoring. Only those tubules in stage VII, as established by maturation of the acrosomes of the spermatids 5 , were counted. 15–30 tubules were counted from each slide. Serial adjacent sections were avoided. The results are plotted in Fig. 1.