Floc'h N L, Obled C, Sève B
Station de Recherches Porcines, INRA, Saint Gilles, France.
Br J Nutr. 1996 Jun;75(6):825-37. doi: 10.1079/bjn19960189.
Threonine oxidation to glycine was investigated in vivo in twelve growing pigs (27.4 kg live weight) fed on one of the following three diets with graded levels of threonine supply: a low-threonine diet (LT), a control well-balanced diet (C) or a high-threonine diet (HT), during 10 h constant infusion of L-[1-13C]threonine and [2-3H]glycine in the cranial vena cava and [1-14C]glycine in the portal vein. 13C-threonine and glycine enrichments and [3H]glycine and [14C]glycine specific radioactivities (SR) were determined at plateau in peripheral venous plasma, liver and pancreas. Glycine production rates calculated from plasma [2-3H]glycine or [1-14C]glycine SR gave similar values suggesting that [1-14C]glycine SR could be used in order to estimate whole-body glycine flux. The high pancreas [1-13C]glycine enrichment provided evidence that the pancreas may be, with the liver, a major site of threonine oxidation to glycine. Moreover, the present findings suggest that threonine transport into the liver could be the limiting step of threonine oxidation in this tissue when dietary threonine supply is low. Total threonine oxidation to glycine, calculated from plasma values of enrichment and specific radioactivity, was low and constant when the estimated absorbed threonine was lower than 4 g/d and increased for higher amounts of absorbed threonine.
在十二头生长猪（活重27.4千克）体内研究了苏氨酸氧化为甘氨酸的情况。这些猪分别饲喂以下三种苏氨酸供应水平分级的日粮之一：低苏氨酸日粮（LT）、对照平衡日粮（C）或高苏氨酸日粮（HT）。在向颅腔静脉持续输注L-[1-¹³C]苏氨酸和[2-³H]甘氨酸以及向门静脉输注[1-¹⁴C]甘氨酸的10小时期间进行研究。在周围静脉血浆、肝脏和胰腺达到稳定状态时，测定¹³C-苏氨酸和甘氨酸的富集情况以及[³H]甘氨酸和[¹⁴C]甘氨酸的比放射性（SR）。根据血浆[2-³H]甘氨酸或[1-¹⁴C]甘氨酸SR计算得出的甘氨酸生成率给出了相似的值，这表明可以使用[1-¹⁴C]甘氨酸SR来估计全身甘氨酸通量。胰腺中高的[1-¹³C]甘氨酸富集证明，胰腺可能与肝脏一样，是苏氨酸氧化为甘氨酸的主要部位。此外，目前的研究结果表明，当日粮苏氨酸供应较低时，苏氨酸转运到肝脏可能是该组织中苏氨酸氧化的限速步骤。根据血浆富集和比放射性值计算得出的苏氨酸氧化为甘氨酸的总量，在估计的吸收苏氨酸低于4克/天时较低且恒定，而在吸收苏氨酸量较高时则增加。
