Layne J R, Lee R E, Heil T L
Department of Biology, Nazareth College, Rochester, New York 14610.
Am J Physiol. 1989 Nov;257(5 Pt 2):R1046-9. doi: 10.1152/ajpregu.1989.257.5.R1046.
During the first few hours of freezing the cardiovascular system must distribute cryoprotectant throughout the body of freeze-tolerant frogs. This study presents initial documentation of the changes in heart rate of wood frogs (Rana sylvatica) during nonlethal freezing. Heart rate was determined by measuring the electrocardiogram of frogs. Within 1 min of the onset of freezing the heart rate nearly doubled to approximately 8.0 beats/min. The heart rate began to slow after the first hour of the freeze, and the heart completely stopped beating near the completion of ice formation approximately 20 h later. Recordings from a single frog revealed that the heart beat resumes within 1 h after thawing and near-normal function is achieved after only a few hours. The release of the latent heat of fusion caused a rise in body temperature (1.7 degrees C) for a few hours and was closely correlated with an increase in the heart rate. However, other factors such as reduction in blood volume, increase in blood viscosity, and progressive hypoxia may prominently influence cardiac function indirectly. Regardless, the heart functions long enough to distribute glucose throughout the body during the first few hours of the freeze.
在耐寒青蛙冷冻的最初几个小时内，心血管系统必须将防冻剂输送到其全身。本研究提供了林蛙（Rana sylvatica）在非致死性冷冻过程中心率变化的初步记录。心率通过测量青蛙的心电图来确定。在冷冻开始后的1分钟内，心率几乎翻倍至约8.0次/分钟。冷冻开始1小时后心率开始减慢，在大约20小时后冰形成接近完成时心脏完全停止跳动。对一只青蛙的记录显示，解冻后1小时内心脏恢复跳动，仅数小时后就能实现接近正常的功能。融化潜热的释放使体温在数小时内升高了1.7摄氏度，且与心率增加密切相关。然而，其他因素，如血容量减少、血液粘度增加和渐进性缺氧，可能会间接地显著影响心脏功能。无论如何，心脏在冷冻的最初几个小时内功能足够长，以便将葡萄糖输送到全身。
