Reasons for reduced activities of 17α-hydroxylase and C17-C20 lyase in spite of increased contents of cytochrome P-450 in mature rat testis fetally irradiated with 60Co

Abstract Pregnant rats received whole body irradiation with 2.6 Gy gamma-ray from a 60 Co source at Day 20 of gestation. When pups were 4 months old, activities of electron transport system and steroid monooxygenase in testes were assayed. The content of total cytochrome P -450 in the irradiated testes had increased to 170% of that in non-irradiated rats, but NADPH-cytochrome P -450 reductase activity had reduced to 36% of the control. Also, amounts of cytochrome bs in testicular microsomal fraction were decreased markedly after irradiation, but no significant change of NADH-cytochrome b 5 reductase activity was observed in the treated pups. Because both 17α-hydroxylase and C 17 –C 20 lyase activities tended to be decreased by fetal irradiation, testosterone production from progesterone and 17α-hydroxyprogesterone was reduced to about 30% of the control. From these results, it has been suggested that the testicular cytochrome P -450 is radioresistant but steroid monooxygenase activities are reduced after the fetal irradiation. We propose that the discrepancy arises from the marked decrement of NADPH-cytochrome P -450 reductase activity.