Rito João, Viegas Ivan, Pardal Miguel A, Jones John G
CNC - Center for Neurosciences and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal; CFE - Center for Functional Ecology, University of Coimbra, Apartado 3046, 3001-401 Coimbra, Portugal; Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal.
CNC - Center for Neurosciences and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal; CFE - Center for Functional Ecology, University of Coimbra, Apartado 3046, 3001-401 Coimbra, Portugal.
Comp Biochem Physiol A Mol Integr Physiol. 2017 Sep;211:41-48. doi: 10.1016/j.cbpa.2017.05.009. Epub 2017 May 26.
Seabass and other carnivorous fish are highly dependent on gluconeogenesis from dietary amino acids to maintain glycemia. Glucose recycling (glucose→C3-intermediate→glucose) may potentiate the effects of glucose administration in sparing amino acid gluconeogenesis. To date, very few measurements of glucose recycling have been reported in fish. Thus, to determine the extent of glucose recycling following a glycemic challenge, juvenile seabass were given an intraperitoneal glucose load (2gkg) enriched with [U-C]glucose. C NMR analysis of plasma glucose C-isotopomers was used to determine the fractional contributions of glucose derived directly from the load versus that from glucose recycling at 48h after the load. Both fed and 21-day fasted fish (20 per condition) were studied. In fasted fish, 18±4% of plasma glucose was directly derived from the load while 13±2% was derived from glucose recycling. In fed fish, the load accounted for 6±1% of plasma glucose levels while glucose recycling contributed 16±4%. C NMR analysis of plasma lactate revealed C-isotopomers corresponding to the expected C3-intermediates of peripheral [U-C]glucose catabolism indicating that circulating lactate was a key intermediate in glucose carbon recycling under these conditions. In conclusion, glucose recycling was shown to contribute a significant portion of plasma glucose levels in both fed and fasted seabass 48h after an intraperitoneal glucose challenge and circulating lactate was shown to be an intermediate of this pathway.
海鲈和其他肉食性鱼类高度依赖从膳食氨基酸进行糖异生来维持血糖水平。葡萄糖再循环（葡萄糖→C3中间体→葡萄糖）可能会增强葡萄糖给药在节省氨基酸糖异生方面的作用。迄今为止，鱼类中关于葡萄糖再循环的测量报道非常少。因此，为了确定血糖挑战后葡萄糖再循环的程度，给幼年海鲈腹腔注射富含[U-C]葡萄糖的葡萄糖负荷（2g/kg）。在负荷后48小时，利用血浆葡萄糖C-同位素异构体的13C NMR分析来确定直接来自负荷的葡萄糖与来自葡萄糖再循环的葡萄糖的分数贡献。对喂食的鱼和禁食21天的鱼（每种情况20条）都进行了研究。在禁食的鱼中，18±4%的血浆葡萄糖直接来自负荷，而13±2%来自葡萄糖再循环。在喂食的鱼中，负荷占血浆葡萄糖水平的6±1%，而葡萄糖再循环贡献了16±4%。血浆乳酸的13C NMR分析揭示了与外周[U-13C]葡萄糖分解代谢预期的C3中间体相对应的C-同位素异构体，表明在这些条件下循环乳酸是葡萄糖碳再循环的关键中间体。总之，在腹腔注射葡萄糖挑战后48小时，葡萄糖再循环在喂食和禁食的海鲈中均对血浆葡萄糖水平有显著贡献，并且循环乳酸被证明是该途径的中间体。
