Ectotherms survive exposure to subzero temperatures through freeze tolerance or freeze avoidance. Among vertebrate ectotherms, glucose is commonly used as a cryoprotectant in freeze tolerant strategies and as an osmolyte in freeze avoidant strategies, while also functioning as a metabolic substrate. Whereas some lizard species are capable of both freeze tolerance and freeze avoidance, Podarcis siculus is limited to freeze avoidance through supercooling. We hypothesized that, even in a freeze-avoidant species such as P. siculus, plasma glucose would accumulate with cold acclimation and would increase in response to acute exposure to subzero temperatures. To investigate this, we tested whether plasma glucose concentration and osmolality would increase in response to a subzero cold challenge before and after cold acclimation. In addition, we examined the relationship between metabolic rate, cold acclimation, and glucose by measuring metabolic rate during the cold challenge trials. We found that plasma glucose increased during the cold challenge trials, and that the increase was more pronounced after cold acclimation. However, baseline plasma glucose decreased throughout cold acclimation. Interestingly, total plasma osmolality did not change, and the increase in glucose only slightly altered freezing point depression. Metabolic rate during the cold challenge decreased after cold acclimation, and changes in respiratory exchange ratio suggest an increased relative use of carbohydrates. Overall, our findings demonstrate an important role for glucose in the response of P. siculus to an acute cold challenge, thus adding evidence for glucose as an important molecule for overwintering ectotherms that use freeze avoidant strategies.

变温动物通过耐受冷冻或避免冷冻而在零度以下的温度下生存。在变温脊椎动物中，葡萄糖通常用作耐冻策略中的冷冻保护剂和避免冷冻策略中的渗透剂，同时还充当代谢底物。虽然某些蜥蜴物种能够同时耐受冰冻和避免冰冻，但腹足蜥只能通过过冷来避免冰冻。我们假设，即使是像P. siculus这样的抗冻物种，血浆葡萄糖会随着冷适应而积累，并且会因急性暴露于零度以下的温度而增加。为了研究这一点，我们测试了在冷适应之前和之后血浆葡萄糖浓度和渗透压是否会因应对零度以下的寒冷挑战而增加。此外，我们通过测量冷挑战试验期间的代谢率来检查代谢率、冷适应和葡萄糖之间的关系。我们发现，在寒冷挑战试验期间，血浆葡萄糖增加，并且在冷驯化后增加更加明显。然而，在冷驯化过程中基线血浆葡萄糖下降。有趣的是，总血浆渗透压没有改变，并且葡萄糖的增加仅略微改变了冰点降低。冷适应后，寒冷挑战期间的代谢率下降，呼吸交换率的变化表明碳水化合物的相对使用增加。总的来说，我们的研究结果表明葡萄糖在反应中发挥着重要作用P. siculus应对急性寒冷挑战，从而增加了葡萄糖作为使用避免冷冻策略的越冬变温动物的重要分子的证据。