The life-history patterns that animals display are a product of their ability to maximize reproductive performance while concurrently balancing numerous metabolic demands. For example, the energetic costs of reproduction may reduce an animal’s ability to support self-maintenance and longevity. In this work, we evaluated the impact of parity on mitochondrial physiology in laboratory mice. The theory of mitohormesis suggests that modest exposure to reactive oxygen species can improve performance, while high levels of exposure are damaging. Following this theory, we hypothesized that females that experienced one bout of reproduction (primiparous) would display improved mitochondrial capacity and reduced oxidative damage relative to non-reproductive (nulliparous) mice, while females that had four reproductive events (multiparous) would have lower mitochondrial performance and greater oxidative damage than both nulliparous and primiparous females. We observed that multiple reproductive events enhanced the mitochondrial respiratory capacity of liver mitochondria in females with high body mass. Four-bout females showed a positive relationship between body mass and mitochondrial capacity. In contrast, non-reproductive females showed a negative relationship between body mass and mitochondrial capacity and primiparous females had a slope that did not differ from zero. Other measured variables, too, were highly dependent on body mass, suggesting that a female’s body condition has strong impacts on mitochondrial physiology. We also evaluated the relationship between how much females allocated to reproduction (cumulative mass of all young weaned) and mitochondrial function and oxidative stress in the multiparous females. We found that females that allocated more to reproduction had lower basal respiration (state 4), lower mitochondrial density, and higher protein oxidation in liver mitochondria than females that allocated less. These results suggest that, at least through their first four reproductive events, female laboratory mice may experience bioenergetic benefits from reproduction but only those females that allocated the most to reproduction appear to experience a potential cost of reproduction.

中文翻译：

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实验室小鼠（Mus musculus）的线粒体生理学随胎次和体重而变化

动物展示的生活史模式是它们最大限度地提高繁殖性能同时平衡众多代谢需求的能力的产物。例如，繁殖的能量成本可能会降低动物维持自我维持和长寿的能力。在这项工作中，我们评估了胎次对实验室小鼠线粒体生理学的影响。有丝分裂理论表明，适度暴露于活性氧可以提高性能，而高水平的暴露则具有破坏性。根据这一理论，我们假设经历了一轮生殖（初产）的雌性与非生殖（初产）小鼠相比，线粒体能力提高，氧化损伤减少，而有四次生殖事件（经产）的雌性与未产和初产雌性相比，线粒体性能较低，氧化损伤更大。我们观察到多个生殖事件增强了高体重女性肝线粒体的线粒体呼吸能力。四回合的女性表现出体重和线粒体容量之间的正相关关系。相比之下，非生殖雌性在体重和线粒体能力之间呈负相关，初产雌性的斜率不为零。其他测量变量也高度依赖于体重，这表明女性的身体状况对线粒体生理有很大影响。我们还评估了有多少雌性分配给繁殖（所有断奶幼仔的累积质量）与多产雌性的线粒体功能和氧化应激之间的关系。我们发现，分配更多用于繁殖的雌性比分配较少的雌性具有更低的基础呼吸（状态 4）、更低的线粒体密度和更高的肝线粒体蛋白质氧化。这些结果表明，至少在前四次繁殖事件中，雌性实验室小鼠可能会​​从繁殖中获得生物能量益处，但只有那些分配最多繁殖的雌性才会经历潜在的繁殖成本。我们发现，分配更多用于繁殖的雌性比分配较少的雌性具有更低的基础呼吸（状态 4）、更低的线粒体密度和更高的肝线粒体蛋白质氧化。这些结果表明，至少在前四次繁殖事件中，雌性实验室小鼠可能会​​从繁殖中获得生物能量益处，但只有那些分配最多繁殖的雌性才会经历潜在的繁殖成本。我们发现，分配更多用于繁殖的雌性比分配较少的雌性具有更低的基础呼吸（状态 4）、更低的线粒体密度和更高的肝线粒体蛋白质氧化。这些结果表明，至少在前四次繁殖事件中，雌性实验室小鼠可能会​​从繁殖中获得生物能量益处，但只有那些分配最多繁殖的雌性才会经历潜在的繁殖成本。