Glucose tolerance declines with age in a long-lived rodent species ( Octodon degus )

Abstract Type 2 diabetes is characterized by elevated blood glucose levels and poor glucose tolerance, which are generally attributed to insulin dysfunction. The prevalence of type 2 diabetes increases with age in humans. The Chilean rodent Octodon degus can spontaneously develop diabetes in captivity, along with comorbidities including cataracts and obesity. Therefore, we hypothesized that glucose tolerance decreases with age in captive degus. To assess glucose tolerance, we fasted the animals overnight and then measured blood glucose before and after a glucose bolus, where higher integrated blood glucose levels above baseline indicated worse glucose tolerance. Our hypothesis was supported, as 48- and 60-month-old degus had significantly higher integrated glucose levels than 3-, approximately 10- and 36-month-old degus, although we found that this trend was stronger in females than in males. However, we found that baseline fasting glucose levels did not significantly vary with age. Future exploration is needed to determine the cause of reduced glucose tolerance in degus, either by examining circulating insulin levels or conducting insulin tolerance tests. In the context of evolutionary theories of ageing, it would be interesting to see if traits related to reduced glucose tolerance are beneficial early in life, especially in nutritionally challenging environments.