Spermatogonial behavior in rats during radiation-induced arrest and recovery after hormone suppression

Ionizing radiation has been shown to arrest spermatogenesis despite the presence of surviving stem spermatogonia, by blocking their differentiation. This block is a result of damage to the somatic environment and is reversed when gonadotropins and testosterone are suppressed, but the mechanisms are still unknown. We examined spermatogonial differentiation and Sertoli cell factors that regulate spermatogonia after irradiation, during hormone suppression, and after hormone suppression combined with Leydig cell elimination with ethane dimethane sulfonate. These results showed that the numbers and cytoplasmic structure of Sertoli cells are unaffected by irradiation, onlyafewtypeAundifferentiated(A_und) spermatogonia andevenfewertypeA1 spermatogonia remained, and immunohistochemical analysis showed that Sertoli cells still produced KIT ligand (KITLG) and glial cell line-derived neurotrophic factor (GDNF). Some of these cells expressed KITreceptor, demonstrating thatthe failureofdifferentiation was notaresultofthe absenceofthe KITsystem. Hormone suppression resulted inan increasein A_und spermatogonia within 3 days, a gradual increase in KIT-positive spermatogonia, and differentiation mainly to A₃ spermatogonia after 2 weeks. KITL (KITLG) protein expression did not change after hormone suppression, indicating that it is not a factor in thestimulation.However,GDNFincreasedsteadilyafterhormonesuppression, which was unexpectedsince GDNFissupposedtopromote stem spermatogonial self-renewal and not differentiation. We conclude that the primary cause of the block in spermatogonial development is not due to Sertoli cell factors such (KITL\GDNF) or the KIT receptor. As elimination of Leydig cells in addition to hormone suppression resulted in differentiation to the A₃ stage within 1 week, Leydig cell factors were not necessary for spermatogonial differentiation.