Department of Life Sciences and Center for Neurosciences and Cell Biology, University of Coimbra, Rua dos Estudos, Apartado 3126, 3001-401 Coimbra, Portugal.
Metab Eng. 2010 Nov;12(6):552-60. doi: 10.1016/j.ymben.2010.08.002. Epub 2010 Aug 24.
Hepatic glycogen is formed by direct and indirect pathways whose activities reflect altered nutrition or disease. Direct/indirect pathway measurements often involve test meals where ∼ 10% of carbohydrate is galactose, but its effects on direct/indirect pathway estimates are unknown. Therefore, direct/indirect pathway contributions in 24-h fasted rats given 2g/kg 100% glucose (GLU, n=6) or 90% glucose-10% galactose (GLU+GAL, n=6) were measured by [U-(13)C]glucose dilution and by position-5/position-2 glycogen enrichment (H5/H2) from 2H(2)O. For GLU+GAL, galactose glycogenesis was independently measured with [1-(13)C]galactose. Glycogenesis was equivalent in both groups but for GLU+GAL, 23 ± 4% of glycogen was derived from galactose. [U-(13)C]glucose reported a 30 ± 3% direct pathway contribution to glycogenesis for GLU but only 20 ± 3% for GLU+GAL (p=0.012 vs. GLU). H5/H2 yielded identical direct pathway estimates (32 ± 3% GLU, 29 ± 6% GLU+GAL). Thus, galactose glycogenesis was undetected by H5/H2 while [U-(13)C]glucose reported a reduced direct/indirect pathway ratio. With [1-(13)C]galactose also present, correct glycogenic source contributions were obtained.
肝糖原可通过直接和间接途径形成，其活性反映了营养改变或疾病状态。直接/间接途径的测定通常涉及测试餐，其中约 10%的碳水化合物为半乳糖，但它对半乳糖对直接/间接途径估计的影响尚不清楚。因此，24 小时禁食大鼠分别给予 2g/kg 100%葡萄糖（GLU，n=6）或 90%葡萄糖-10%半乳糖（GLU+GAL，n=6），通过[U-(13)C]葡萄糖稀释和 2H(2)O 标记的位置-5/位置-2 糖原富集（H5/H2）测定直接/间接途径的贡献。对于 GLU+GAL，用[1-(13)C]半乳糖独立测定半乳糖的糖异生。两组的糖异生量相等，但 GLU+GAL 中有 23±4%的糖原来源于半乳糖。[U-(13)C]葡萄糖报告 GLU 的糖异生直接途径贡献为 30±3%，但 GLU+GAL 仅为 20±3%（p=0.012 与 GLU 相比）。H5/H2 得到的直接途径估计值相同（GLU 为 32±3%，GLU+GAL 为 29±6%）。因此，H5/H2 未能检测到半乳糖的糖异生，而[U-(13)C]葡萄糖报告直接/间接途径比值降低。当同时存在[1-(13)C]半乳糖时，可以获得正确的糖异生来源贡献。
