Physiological responses in vitamin C system during hibernation in juvenile Chinese soft-shelled turtle Pelodiscus sinensis

Vitamin C (Vc) is an important antioxidant that helps turtles tolerating stressful environment. This work quantified changes in tissue Vc levels during winter hibernation in the soft-shelled turtle Pelodiscus sinensis, to reveal the stress response pattern of tissue Vc during hibernation and contribute basic data for turtle culture. We sampled juvenile soft-shelled turtles at pre-hibernation (17.0°C mud temperature; MT), during hibernation (5.8°C MT) and after arousal (20.1°C MT) in the field. The transcript levels of the gene encoding L-gulonolactone oxidase (GLO), the key enzyme for Vc synthesis, decreased significantly during hibernation. However, GLO activity did not match the GLO transcription patterns and remained stable during hibernation, and showed temperature-dependent kinetic characteristics. Vitamin C levels in the brain, liver, kidney, and spleen (but not muscle) all decreased significantly during hibernation, but recovered to pre-hibernation levels or even higher levels after arousal. The soft-shelled turtle endured 5 months of hibernation with no significant oxidative damage in most tissues, except in the spleen. Splenic Vc was nearly exhausted during hibernation, accompanied by a significantly elevated malonaldehyde (MDA) level. Although the high level of oxidative damage quickly decreased after arousal, the potential tissue damage in the spleen during hibernation might account for the weakened immune capacity of turtles after hibernation.