Rivera R M, Hansen P J
Department of Animal Sciences, University of Florida, PO Box 110920, Gainesville, FL 32611-0920, USA.
Reproduction. 2001 Jan;121(1):107-15.
Embryonic development is inhibited by exposure of cultured embryos to high temperatures. However, culture temperatures used to demonstrate the effects of heat on development have been higher than the body temperatures experienced typically by heat-stressed cows. The aim of this study was to determine whether exposing bovine oocytes and embryos to temperatures characteristic of body temperatures of heat-stressed cows would affect embryonic development in vitro. The CO2 percentage of the gas phase was adjusted in all experiments to prevent pH changes in the medium caused by decreased solubility of CO2 at high temperatures. Fertilization of oocytes at 41.0 degrees C reduced cleavage rate and the percentage of oocytes that became blastocysts compared with at 38.5 degrees C. There was no deleterious effect of fertilization at 40.0 degrees C. When putative zygotes and two-cell embryos were exposed to a range of temperatures from 38.5 to 41.0 degrees C for 3, 6, 9 or 12 h, heat shock reduced the number that developed to the blastocyst stage but only after exposure to 41.0 degrees C for 9 or 12 h. In addition, it was tested whether low O2 tension would reduce the detrimental effects of heat shock. The deleterious effect of 41.0 degrees C was not dependent upon oxygen content or the gas mixture used for culture (5% versus 20.95% O2), indicating that the deleterious effects of heat shock did not depend upon a high O2 environment. In the final experiment, embryos were exposed to 24 h fluctuations in temperature designed to mimic the rectal temperatures of cows exposed to heat stress. Exposure of embryos to this pattern of temperatures starting after fertilization reduced development when embryos were exposed to this environment for 8 days but not when embryos were exposed for 1 day only. These findings indicate that embryonic development can be disrupted by a short-term severe or a prolonged mild heat shock and that the effects of heat shock are not artefacts of changes in pH or high oxygen tension.
将培养的胚胎暴露于高温会抑制胚胎发育。然而，用于证明热对发育影响的培养温度高于热应激奶牛通常经历的体温。本研究的目的是确定将牛卵母细胞和胚胎暴露于热应激奶牛体温特征的温度下是否会影响体外胚胎发育。在所有实验中均调整气相中的二氧化碳百分比，以防止高温下二氧化碳溶解度降低导致培养基pH值变化。与在38.5℃受精相比，在41.0℃对卵母细胞进行受精会降低卵裂率和发育成囊胚的卵母细胞百分比。在40.0℃受精没有有害影响。当假定的合子和二细胞胚胎在38.5至41.0℃的一系列温度下暴露3、6、9或12小时时，热休克会减少发育到囊胚阶段的数量，但仅在暴露于41.0℃9或12小时后才会出现这种情况。此外，还测试了低氧张力是否会降低热休克的有害影响。41.0℃的有害影响不取决于氧气含量或用于培养的气体混合物（5%对20.95%氧气），这表明热休克的有害影响不取决于高氧环境。在最后一个实验中，胚胎暴露于旨在模拟热应激奶牛直肠温度的24小时温度波动中。受精后开始将胚胎暴露于这种温度模式下，当胚胎在这种环境中暴露8天时发育会减少，但仅暴露1天时则不会。这些发现表明，短期严重或长期轻度热休克会破坏胚胎发育，并且热休克的影响不是pH值变化或高氧张力造成的假象。
