Abstract: The purpose of this experiment was to explore the effects of dietary supplementation of different levels of rutin on alleviating testicular tissue damage in heat-stressed mice. Thirty 5-week-old male mice of ICR strain with similar body weight (20-22 g) were randomly divided into 5 groups. Mice in each group were fed basal diet supplemented with 0 (CON group), 0 (HS group), 250 (HS+R250), 500 (HS+R500) and 1 000 (HS+R1000) mg·kg^-1 rutin for 10 days, respectively. Except for control group (CON), all mice were treated in an incubator at 42℃ between 10:00 and 14:00 every day for 8 consecutive days, and then slaughtered for sampling and analysis. The results showed as follows:1) Compared with CON group, the testis index of mice in HS group had no significant change (P>0.05), but dietary 250 mg·kg^-1 rutin significantly increased the testis index of mice under heat stress (P<0.05). The results of mouse testicular tissue sections showed that compared with the CON group, the cross-sectional area and diameter of the seminiferous tubules in the HS group were significantly reduced (P<0.05), and the rate of spermatogenic cell shedding was significantly increased (P<0.05). Compared with the HS group, the cross-sectional area of the seminiferous tubules in the HS+R250 group was significantly increased (P<0.05), the rate of spermatogenic cells shedding was significantly reduced (P<0.05), while the rate of spermatogenic cell shedding in the HS+R500 group was significantly reduced (P<0.05), and the diameter of the seminiferous tubules in the HS+R1000 group was significantly increased (P<0.05); There was no significant difference in testis index, seminiferous tubule diameter and seminiferous tubule shedding ratio between the rutin-treated groups and the CON group (P>0.05), however, the cross-sectional area of the seminiferous tubules in the HS+R250 group was significantly higher than that in the CON group (P<0.05). 2) Compared with CON group, malondialdehyde (MDA) content in testis tissue of HS group increased significantly (P<0.05), while total antioxidant capacity (T-AOC), glutathione (GSH) content and the mRNA expression of hemolytic enzyme 1 (HO-1) in testis tissue of mice were significantly decreased (P<0.05). The supplementation of 250 mg·kg^-1 rutin significantly decreased the MDA content (P<0.05), increased the T-AOC and GSH content in testis of heat-stressed mice (P<0.05), and enhanced nuclear factor E2 related factors 2 (Nrf2), HO-1 and glutathione peroxidase (GSH-Px) mRNA expression (P<0.05), while the supplementation of 500 and 1 000 mg·kg^-1 rutin also significantly increased the GSH content (P<0.05); Compared with the CON group, except that the Nrf2 mRNA expression in the HS+R250 group was significantly higher than that in the CON group (P<0.05), there were no significant changes in the antioxidant genes and enzyme activity indexes in the testis tissue of the heat-stressed mice in the rutin groups. (P>0.05). 3) The mRNA expression levels of nuclear factor -κB (NF-κB), Toll-like receptor 4 (TLR-4) and Bax in testis of heat-stressed mice were significantly increased (P<0.05), while the expression level of Bcl-2 was significantly decreased (P<0.05). Dietary supplementation of 250 mg·kg^-1 rutin significantly reduced the mRNA expression of NF-κB, TLR-4, myeloid differentiation factor 88 (MyD88), interleukin-Iβ (IL-1β) and Bax (P<0.05), enhanced the expression level of Bcl-2 (P<0.05); Adding 500 mg·kg^-1 rutin to the diet significantly reduced the expression of NF-κB and TLR-4 (P<0.05), while adding 1 000 mg·kg^-1 rutin significantly increased the expression of Bcl-2 (P<0.05). There was no significant difference in the expression of immune and proliferation apoptosis-related genes in mouse testis between the rutin groups and the CON group (P>0.05). These results suggest that dietary supplementation with appropriate dose of rutin can improve the morphology and function of testis in heat-stress mice, and the mechanism may be closely related to the relief of oxidative stress through Nrf2 signaling pathway, the inhibition of inflammatory response through TLR-4/NF-κB signaling pathway and the regulation of Bax/Bcl-2 mRNA expression. The effect of dietary 250 mg·kg^-1 rutin was better under the experimental conditions.

Key words: heat stress, mice, testis, rutin, oxidative stress, inflammation, tissue damage