Impaired detoxification of reactive oxygen and consequent oxidative stress in experimentally cryptorchid rat testis

Abstract

The effect of experimental cryptorchidism on the level of oxidative stress and antioxidant functions in rat testis was studied. Adult male Sprague- Dawley rats were rendered unilaterally cryptorchid (by suturing one testis to the abdominal wall) and killed 1, 3, or 7 days after the operation. As an indicator of oxidative stress, lipid peroxidation was measured by the diene conjugation method in testis homogenates. The activities of the antioxidant enzymes were determined either in the 10 000 x g supernatant fraction (glutathione [GSH] peroxidase, GSH transferase, hexose monophosphate shunt) or in crude testis homogenates (superoxide dismutase, catalase). An expected reduction (48%) in weight of the abdominal testes was evident by postoperative Day 7. The catalytic activities per testis of superoxide dismutase (Cu/Zn form) and catalase were found to decrease in cryptorchidism. The effect was seen on the first postoperative day and was most profound on Day 7 after surgery. The principal antioxidant enzyme, superoxide dismutase, was most sensitive to cryptorchidism, the activity in the abdominal testes being 74% or 85% (per gram of tissue or per whole testis, respectively; p < 0.01). After impairment of the reactive oxygen detoxifying capacity, lipid peroxidation was increased in the abdominal testis by 46% (p < 0.01) on postoperative Day 7. Slight concomitant increases were detected in the activities of GSH-peroxidase (p < 0.01), GSH-transferase (p < 0.001), and the hexose monophosphate shunt (p < 0.001). This effect was seen only when calculated per gram of tissue, not per whole testis. When decapsulated control testes were incubated in HEPES-buffered Medium 199, 18% (p < 0.05) or 42% (p < 0.01) of superoxide dismutase activity was lost after 3 h at 37°C or 40°C, respectively, whereas the other enzyme activities were not affected. This result suggests that cryptorchidism particularly affects superoxide dismutase because of elevated abdominal temperature. In conclusion, the present investigation showed that superoxide dismutase activity of rat testis is sensitive to inactivation by elevated temperatures. In addition, the catalase activity is decreased, and thus the reactive oxygen detoxifying capacity is reduced, resulting in increased oxidative stress of the cryptorchid rat testis. These events may be implicated in the impaired spermatogenesis and increased tendency to malignant transformation of the cryptorchid testis.