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Many physiological activities in amphibians show rhythmic changes to adapt to ambient light conditions. However, the effects of photoperiod variation on the immune and antioxidant status and their possible correlation with different tissues have not been reported in Dybowski's frog, Rana dybowskii. In this study, the specific activities of immune and antioxidant enzymes in R. dybowskii under different photoperiods were evaluated. The results demonstrated that the photoperiod significantly impacted antioxidant enzymes and immune enzymes in Dybowski's frog. In terms of antioxidant enzyme activity, catalase (CAT) and superoxide dismutase (SOD) activities in frogs at 6 L:18D and 0 L:24D were significantly higher than those at 18 L:6D and 24 L:0D, respectively. Further, the activities of these enzymes increased during the dark phase and decreased during the light phase. The malondialdehyde (MDA) content decreased significantly with the decrease in photoperiod time. Lysozyme (LZM) activity in serum and the liver decreased with a prolonged photoperiod. LZM activity in the dark cycle was higher, but the peak activity in skin occurred at noon. Thus, long-term light exposure may cause oxidative stress in Dybowski's frog. Accordingly, a 6 L:18D photoperiod may be suitable for optimum physiological functions of this species. [ABSTRACT FROM AUTHOR]

There are few studies on the relationship between photoperiod and the melatonin cycle in amphibians. To elucidate the role of the photoperiodically modulated endogenous melatonin cycle in different tissues of Dybowski's frog (Rana dybowskii), its serum, liver, whole brain, skin, and eyeballs were collected under five photoperiods, and the daily variation in melatonin concentration was determined via high-performance liquid chromatography. Compared with the control group (12 L:12 D), melatonin concentration was increased under photoperiods 0 L:24 D and 6 L:18 D in serum, and the concentration peaked at 00:00 under photoperiod 0 L:24 D. This trend was synchronized with the peak melatonin concentration in the retinal, liver, and whole-brain tissues. After 24 h of light exposure, no significant daily variation was observed under photoperiod 24 L:0 D. Furthermore, we observed a significant peak at 04:00 in the serum under photoperiod 18 L:6 D. However, we observed the opposite trend in the circadian rhythm of the skin tissue. Our results underscore the high sensitivity of melatonin content to different photoperiods. These findings may have real-world implications in terms of furthering our understanding of circadian rhythms disruption induced by exposure to different photoperiods. [ABSTRACT FROM AUTHOR]