Champagne Cory D, Houser Dorian S, Crocker Daniel E
Department of Ecology and Evolutionary Biology, University of California. Santa Cruz, CA 95060, USA.
Am J Physiol Regul Integr Comp Physiol. 2006 Oct;291(4):R1129-37. doi: 10.1152/ajpregu.00570.2005. Epub 2006 May 4.
Fasting is associated with a series of physiological responses that protect body tissues from degradation by efficiently using expendable energy reserves while sparing protein. Lactation requires the mobilization of maternal nutrients for milk synthesis. The rare life history trait of fasting simultaneous with lactation results in the conflicting demands of provisioning offspring while meeting maternal metabolic costs and preserving maternal tissues for her own survival and future reproduction. Certain tissues continue to require glucose for operation during fasting and might constrain tissue mobilization for lactogenesis due to a need for gluconeogenic substrates. This study investigated glucose flux, glucose cycle activity, and the influence of regulatory hormones in fasting lactating northern elephant seals. Measurements were taken early (5 days) and late (21 days) during the lactation period and, as a nonlactating comparison, after the completion of molting. Glucose cycle activity was highly variable in all study groups and did not change over lactation (P > 0.3), whereas endogenous glucose production decreased during lactation (t = -3.41, P = 0.008). Insulin and insulin-to-glucagon molar ratio decreased across lactation (t = 6.48, 4.28; P = 0.0001, 0.002), while plasma cortisol level increased (t = 4.15, P = 0.002). There were no relationships between glucose production and hormone levels. The glucose production values measured exceeded that predicted from available gluconeogenic substrate, indicating substantial glucose recycling in this species.
禁食与一系列生理反应相关，这些反应通过有效利用可消耗的能量储备同时 sparing protein（此处可能有误，推测应为“节省蛋白质”）来保护身体组织不被降解。哺乳需要调动母体营养物质用于乳汁合成。禁食与哺乳同时发生这种罕见的生活史特征导致了在为后代提供营养的同时满足母体代谢成本以及为自身生存和未来繁殖保留母体组织这两种相互冲突的需求。某些组织在禁食期间仍继续需要葡萄糖来维持运转，并且由于对糖异生底物的需求，可能会限制用于泌乳的组织动员。本研究调查了禁食的哺乳期北方海象的葡萄糖通量、葡萄糖循环活性以及调节激素的影响。在哺乳期早期（5天）和晚期（21天）进行了测量，并且作为非哺乳期对照，在换毛完成后进行了测量。所有研究组的葡萄糖循环活性变化很大，并且在哺乳期没有变化（P>0.3），而内源性葡萄糖生成在哺乳期减少（t = -3.41，P = 0.008）。胰岛素和胰岛素与胰高血糖素的摩尔比在整个哺乳期下降（t = 6.48，4.28；P = 0.0001，0.002），而血浆皮质醇水平升高（t = 4.15，P = 0.002）。葡萄糖生成与激素水平之间没有关系。测得的葡萄糖生成值超过了根据可用糖异生底物预测的值，表明该物种存在大量的葡萄糖再循环。
