Department of Zoology, University of Otago, Dunedin, New Zealand.
J Comp Physiol B. 2011 Aug;181(6):781-92. doi: 10.1007/s00360-011-0561-7. Epub 2011 Mar 4.
The brown tree frog (Litoria ewingii) is the only known Southern Hemisphere vertebrate that can survive full-body freezing. Freezing challenges living organisms in many ways, with ice formation in the body producing a suite of physical and metabolic stresses which can damage cells and tissues. The present study looked at two mechanisms that address some of these stresses: cryoprotectants and ice nucleating agents (INAs). Skin secretions from L. ewingii were sampled along with microhabitat substrate and tested for the presence of INAs, which help control ice formation in the body. L. ewingii plasma was tested for seasonal and freezing-induced changes in both glucose and glycerol, which may have a cryoprotective role in freezing-tolerant frogs. Glycerol levels increased on freezing and decreased on thawing, while glucose levels did not change on freezing but increased on thawing. This suggests that glycerol may be acting as a cryoprotectant, although levels are low compared to other frogs. A clear seasonal change was seen in INA activity, with greater activity in winter than in summer. While potent INAs came from the microhabitat substrate, this work has shown for the first time that skin secretions also contain active INAs.
棕树蛙（Litoria ewingii）是唯一已知的能够全身冷冻存活的南半球脊椎动物。冷冻以多种方式挑战着生物体，冰晶的形成会产生一系列物理和代谢应激，从而损害细胞和组织。本研究着眼于两种机制，它们可以解决其中一些应激问题：抗冻剂和冰核剂（INA）。从棕树蛙的皮肤分泌物、微生境基质中取样，测试是否存在 INA，它有助于控制体内的冰晶形成。测试棕树蛙血浆中葡萄糖和甘油的季节性变化和冷冻诱导变化，它们可能在抗冻青蛙的冷冻耐受中起保护作用。甘油水平在冷冻时增加，在解冻时减少，而葡萄糖水平在冷冻时没有变化，在解冻时增加。这表明甘油可能起到抗冻保护剂的作用，尽管与其他青蛙相比，其水平较低。INA 活性有明显的季节性变化，冬季的活性大于夏季。虽然强烈的 INA 来自微生境基质，但这项工作首次表明，皮肤分泌物也含有活性 INA。
