Specific aims: A few species of frogs are the only vertebrates known to tolerate freezing. This study examines the physiological basis of freeze tolerance in the wood frog, Rana sylvatica. Research will focus on two primary objectives: 1. To characterize systemic and metabolic responses from the onset of ice nucleation in body fluids until ice formation is complete. The specificity of tissue accumulation of glucose and lactate, the distribution of ice and water, and cardiac function will be monitored. Also, the significance of variable freezing and thawing rates will be evaluated. 2. To examine the physiological triggering mechanisms responsible for the rapid mobilization of glucose from the liver. Regulation of glycogenolysis in the liver will be examined in terms of intrinsic and extrinsic (neuroendocrine) controls. Health relatedness and long-term objectives: An ever growing demand exists in the biomedical community for viable, long-term storage of organs to be used for transplantation; however, attempts at the cryopreservation of mammalian organs have met with limited success. From a long-term perspective freeze-tolerant frogs may provide an important vertebrate model system for the study of tissue and organ cryopreservation. Furthermore, a 70-fold increase in blood glucose levels occurs concomitantly with tissue freezing. The accumulated glucose functions as a cryoprotective agent. In other vertebrates this hyperglycemic response would be interpreted as potentially lethal or a severely diabetic state. Therefore, the wood frog may be useful in the study of intermediary metabolism including the regulation of glucose metabolism and hypoxia.