Sexual dimorphism in the architecture of the lung's gas-exchange region.

The lung's only vital function is to provide sufficient gas-exchange surface area (Sa) to meet the organism's needs for oxygen uptake (VO2) and carbon dioxide elimination. A direct linear relation between Sa and VO2 and an inverse linear relation between the size of the lung's gas-exchange units and the species mass-specific VO2 are strongly conserved across species. Within species, Sa increases in response to prolonged (weeks) elevation of VO2. We now report sex-dependent deviations from these relationships that seem to anticipate the need for increased gas-exchange capacity engendered in females by the metabolic demands of pregnancy and lactation. We found that although VO2 almost doubled in rats during pregnancy and lactation, Sa was the same in age-matched virgin, pregnant, and lactating females. However, at the onset of sexual maturity, virgin female rats and mice had higher mass-specific Sa than males of the same species although mass-specific VO2 was identical, within species, in both sexes. In addition, even though mass-specific VO2 was identical in males and females, alveoli were 30% and 50% smaller in female rats and mice, respectively, than males of the same species. We suggest the greater mass-specific Sa and smaller alveoli in females in spite of identical mass-specific VO2 as males were selected for evolutionarily; they help females meet the metabolic demands of reproduction without adding to the energy demands of these periods a requirement to form additional lung. IMAGES:

肺唯一的核心生理功能是提供充足的气体交换表面积（gas-exchange surface area，简称Sa），以满足机体对氧气摄取量（oxygen uptake，简称VO2）和二氧化碳排出的需求。跨物种间，Sa与VO2之间存在直接线性关系，而肺气体交换单位的大小与物种单位体重VO2之间呈负线性关系，且这两种关系在各物种中均高度保守。在同一物种内，Sa会随着VO2长期（数周）升高而增加。本研究现报道了与上述规律存在性别依赖性偏离的现象，该偏离似乎是为了预先适配雌性个体因妊娠与哺乳的代谢需求而产生的气体交换容量提升需求。研究发现，尽管大鼠在妊娠和哺乳期间的VO2几乎翻倍，但同龄未交配、妊娠及哺乳雌性个体的Sa并无差异。然而，在性成熟初期，同物种内的未交配雌性大鼠与小鼠的单位体重Sa均高于雄性个体，尽管两性的单位体重VO2并无差异。此外，尽管两性的单位体重VO2一致，但同物种雌性大鼠与小鼠的肺泡（alveoli）体积分别比雄性小30%与50%。我们认为，尽管雌性与雄性的单位体重VO2一致，但雌性具备更高的单位体重Sa与更小的肺泡，这是演化筛选的结果；该特征可帮助雌性个体满足生殖过程中的代谢需求，同时无需额外生成肺组织，进而避免该时期产生额外的能量消耗。图像：