Hammond K A, Lloyd K C, Diamond J
Department of Physiology, UCLA School of Medicine, Los Angeles, CA 90095-1751, USA.
J Exp Biol. 1996 Feb;199(Pt 2):337-49. doi: 10.1242/jeb.199.2.337.
Using lactation in mice as a model, we sought to determine whether ceilings on sustained energy expenditure reside in the capacities of energy-acquiring and input organs (such as the intestine) or of energy-expending and output organs (such as the mammary glands). To distinguish between these possibilities experimentally, we surgically varied the teat number of lactating mother mice while simultaneously varying their litter size. The energy burden on each teat (i.e. the pup/teat ratio) could thus be varied independently of the energy burden (i.e. litter size) on the mother herself or on her intestine. At each teat number, pup mass proved to be maximal at intermediate litter sizes. At a given pup/teat ratio, mothers with five teats weaned pups no larger than the pups of normal (10-teat) mothers, even though the total energy burden on the former mothers was only half as large. Mothers with only two teats could not wean any pups. Litter size controlled maternal food intake, which in turn controlled intestinal mass and nutrient uptake capacity. Disproportionately high food intake for the smallest litters appears to reflect capital start-up costs of lactation. Pup mass is evidently limited by inadequate suckling stimulation of mammary glands.
以小鼠哺乳期为模型，我们试图确定持续能量消耗的上限是取决于能量获取和输入器官（如肠道）的能力，还是取决于能量消耗和输出器官（如乳腺）的能力。为了通过实验区分这些可能性，我们对哺乳期母鼠的乳头数量进行手术改变，同时改变其窝仔数。这样，每个乳头的能量负担（即幼崽/乳头比例）就可以独立于母鼠自身或其肠道上的能量负担（即窝仔数）而变化。在每个乳头数量下，窝仔质量在中等窝仔数时被证明是最大的。在给定的幼崽/乳头比例下，有五个乳头的母鼠断奶时的幼崽并不比正常（十个乳头）母鼠的幼崽大，尽管前者母鼠的总能量负担只有后者的一半。只有两个乳头的母鼠无法断奶任何幼崽。窝仔数控制着母鼠的食物摄入量，而食物摄入量又反过来控制着肠道质量和营养吸收能力。最小窝仔数的母鼠食物摄入量过高，这似乎反映了哺乳期的启动成本。显然，幼崽质量受到乳腺哺乳刺激不足的限制。
