The trout ventricle has an outer compact layer supplied with well-oxygenated arterial blood from the coronary circulation, and an inner spongy myocardium supplied with oxygen poor venous blood. It was hypothesized that: (1) the spongy myocardium of steelhead trout ( Oncorhynchus mykiss ), given its routine exposure to low partial pressures of oxygen (PO 2 ), would be better able to maintain contractile performance (work) when exposed to acute hypoxia (100 to 10% air saturation) relative to the compact myocardium, and would show little benefit from hypoxic acclimation; and (2) the compact myocardium from hypoxia-acclimated (40% air saturation) fish would be better able to maintain work during acute exposure to hypoxia relative to normoxia-acclimated individuals. Consistent with our expectations, when PO 2 was acutely lowered, net work from the compact myocardium of normoxia-acclimated fish declined more (by ~ 73%) than the spongy myocardium (~ 50%), and more than the compact myocardium of hypoxia-acclimated fish (~ 55%), and hypoxic acclimation did not benefit the spongy myocardium in the face of reduced PO 2 . Further, while hypoxic acclimation resulted in a 25% (but not significant) decrease in net work of the spongy myocardium, the performance of the compact myocardium almost doubled. This research suggests that, in contrast to the spongy myocardium, performance of the compact myocardium is improved by hypoxic acclimation; and supports previous research suggesting that the decreased contractile performance of the myocardium upon exposure to lowered PO 2 may be adaptive and mediated by mechanisms within the muscle itself.

中文翻译：

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低氧驯化对硬头鳟（Oncorhynchus mykiss）海绵状致密心室心肌收缩特性的影响

鳟鱼心室有一个外部致密层，由来自冠状循环的充氧良好的动脉血供应，而内部海绵状心肌则由缺氧的静脉血供应。假设：(1) 铁头鳟鱼 ( Oncorhynchus mykiss ) 的海绵状心肌，由于其常规暴露于低氧分压 (PO 2 )，在暴露于急性缺氧时能够更好地维持收缩性能（工作） （100% 到 10% 空气饱和度）相对于致密心肌，并且从低氧驯化中几乎没有益处；(2) 与常氧适应的个体相比，来自低氧适应（40% 空气饱和度）鱼的致密心肌在急性缺氧暴露期间能够更好地维持工作。与我们的预期一致，当 PO 2 急剧下降时，常氧驯化鱼的致密心肌的净功比海绵状心肌（约 50%）下降更多（约 73%），比缺氧驯化鱼的致密心肌（约 55%）下降更多（约 55%），缺氧驯化PO 2 降低对海绵状心肌无益。此外，虽然缺氧驯化导致海绵状心肌的净功减少 25%（但不显着），但致密心肌的性能几乎翻了一番。这项研究表明，与海绵状心肌相比，低氧驯化可改善致密心肌的性能；并支持先前的研究表明，暴露于降低的 PO 2 时心肌收缩性能下降可能是适应性的，并由肌肉本身的机制介导。