Persistent testicular glycogenolysis and active lipid metabolism during torpor in hibernating Siberian chipmunks.

Numerous hibernating species within the family Sciuridae display distinct hibernation bout patterns and initiate reproductive activities shortly after arousal from torpor. However, the influence of different hibernation phases on testicular function has not yet been fully elucidated. To address this knowledge gap, we investigated alterations in testicular morphology and glycogen as well as lipid metabolism in Siberian chipmunks (Tamias sibiricus) across key physiological stages associated with the hibernation cycle. We found that serum lipid levels were high during torpor, while glucose peaked during interbout arousal. Although body weight decreased, testicular mass increased during hibernation, accompanied by stable levels of testosterone, follicle-stimulating hormone, and luteinizing hormone. Spermatogonia density dropped, but spermatocytes increased, along with larger seminiferous tubules and a thicker spermatogenic epithelium. Glycogen content and glycogenosome density were significantly reduced compared to pre-hibernation levels, accompanied by decreased glycogen synthase activity and elevated phosphorylase activity. Fatty acid levels remained high throughout hibernation, though triglycerides were lower during interbout arousal than in torpor. Fatty acid synthase and acetyl-CoA carboxylase activities increased during interbout arousal, whereas lipoprotein lipase and glycerol kinase activities were elevated during torpor. Together, these results are consistent with a coordinated shift between glucose- and lipid-related pathways across torpor-arousal cycles, which may be associated with maintaining testicular energy homeostasis during hibernation.