Inhibin B is a more sensitive marker of spermatogenetic damage than FSH inthe irradiated non-human primate model

This study evaluated the effect of bilateral testicular irradiation (2 Gy) on reproductive hormones, testicular volume (TV) and sperm parameters in si x adult cynomolgus monkeys. Hormone levels (FSH, inhibin B and testosterone (T)) were determined to find the most valuable endocrine marker of irradia tion-induced damage. All parameters were analysed at weekly intervals for 1 4 weeks. Histological evaluation of both testes was performed at week 14 af ter irradiation when one monkey was castrated and at week 27 when the remai ning five monkeys were bilaterally biopsied. A decrease in body weight, TV (30% of the pre-treatment size) and sperm count was observed after irradiat ion. Severe oligozoospermia was achieved throughout the study but azoosperm ia was recorded only occasionally. Histological evaluation revealed a heter ogeneous picture with patchy arrangement of seminiferous tubules containing advanced germ cell types. An increase (P<0.05) in FSH levels and, to a les ser degree also in T levels, occurred several weeks after irradiation. Inhi bin B levels showed a sharp decline (P<0.001) as soon as 1 week after irrad iation. FSH and inhibin B did not return to baseline levels during the obse rvation period. A negative correlation was found between FSH and inhibin B values (r= - 0.35, P<0.001). Inhibin B correlated positively with testis vo lume (r=0.73, P<0.001) and sperm counts (r=0.55, P<0.01). In conclusion, th is study shows that inhibin B represents an early and more sensitive marker of testicular damage than FSH. Furthermore, the rapid fall of inhibin B af ter irradiation suggests that this hormone is a direct parameter of premeio tic germ cell proliferation.