FIG. 8.

Proposed mechanism of HD-mediated attenuation of germ cell apoptosis. (A) Testis after x-ray exposure; (B) testis after combined HD and x-ray exposure. Sertoli cells normally support and nurture the developing germ cells. After a direct toxic insult to germ cells by x-ray exposure, the affected germ cells increase expression of Fas and subsequently undergo apoptosis (A). Disruption of Sertoli cell support by HD pretreatment results in an adaptive response of the germ cells, indicated by the thicker black outline around the germ cell, so that upon x-ray exposure they fail to upregulate Fas and are less sensitive to x-ray effects (B).