Biology Department, University of Ottawa, Ottawa, Ontario, Canada.
J Exp Biol. 2010 Nov 15;213(Pt 22):3802-9. doi: 10.1242/jeb.048512.
Current understanding of lactate metabolism in fish is based almost entirely on the interpretation of concentration measurements that cannot be used to infer changes in flux. The goals of this investigation were: (1) to quantify baseline lactate fluxes in rainbow trout (Oncorhynchus mykiss) under normoxic conditions; (2) to establish how changes in rates of lactate appearance (R(a)) and disposal (R(d)) account for the increase in blood lactate elicited by hypoxia; and (3) to identify the tissues responsible for lactate production. R(a) and R(d) lactate of rainbow trout were measured in vivo by continuous infusion of [U-(14)C]lactate in trout exposed to 25% O(2) saturation or maintained in normoxia for 90 min. In normoxic fish, R(a) lactate decreased from 18.2 to 13.1 μmol kg(-1) min(-1) and R(d) lactate from 19.0 to 12.8. R(a) and R(d) were always matched, thereby maintaining a steady baseline blood lactate concentration of ∼0.8 mmol l(-1). By contrast, the hypoxic fish increased blood lactate to 8.9 mmol l(-1) and R(a) lactate from 18.4 to 36.5 μmol kg(-1) min(-1). This stimulation of anaerobic glycolysis was unexpectedly accompanied by a 52% increase in R(d) lactate from 19.9 to 30.3 μmol kg(-1) min(-1). White muscle was the main producer of lactate, which accumulated to 19.2 μmol g(-1) in this tissue. This first study of non-steady-state lactate kinetics in fish shows that the increase in lactate disposal elicited by hypoxia plays a strategic role in reducing the lactate load on the circulation. Without this crucial response, blood lactate accumulation would double.
目前对鱼类乳酸代谢的理解几乎完全基于对浓度测量的解释，而这些解释无法用来推断通量的变化。本研究的目的是：（1）在常氧条件下定量测定虹鳟（Oncorhynchus mykiss）的基础乳酸通量；（2）确定乳酸生成率（R(a)）和清除率（R(d)）的变化如何解释低氧引起的血液乳酸增加；（3）确定产生乳酸的组织。通过连续输注[U-(14)C]乳酸，在暴露于 25% O2 饱和度或在常氧下维持 90 min 的虹鳟体内测量 R(a)和 R(d)乳酸。在常氧鱼中，R(a)乳酸从 18.2 降至 13.1 μmol kg(-1) min(-1)，R(d)乳酸从 19.0 降至 12.8。R(a)和 R(d)总是匹配的，从而维持稳定的基础血液乳酸浓度约为 0.8 mmol l(-1)。相比之下，缺氧鱼的血液乳酸增加到 8.9 mmol l(-1)，R(a)乳酸从 18.4 增加到 36.5 μmol kg(-1) min(-1)。这种无氧糖酵解的刺激出乎意料地伴随着 R(d)乳酸从 19.9 增加到 30.3 μmol kg(-1) min(-1)，增加了 52%。白色肌肉是乳酸的主要产生者，在该组织中积累了 19.2 μmol g(-1)。这是首次在鱼类中研究非稳态乳酸动力学的研究表明，低氧引起的乳酸清除增加在降低循环中乳酸负荷方面起着战略性作用。如果没有这个关键的反应，血液乳酸的积累将增加一倍。
