United States Department of Agriculture/Agricultural Research Service Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA.
Am J Physiol Endocrinol Metab. 2012 Dec 1;303(11):E1348-53. doi: 10.1152/ajpendo.00399.2012. Epub 2012 Oct 16.
Citrulline is an amino acid synthesized in the gut and utilized for the synthesis of the conditionally essential amino acid arginine. Recently, the origin of the ornithine utilized for citrulline synthesis has become a matter of discussion. Multiple physiological factors may have contributed to the differences found among different researchers; one of these is the developmental stage of the subjects studied. To test the hypothesis that during the neonatal period de novo synthesis is the main source of ornithine for citrulline synthesis, neonatal piglets were infused intravenously or intragastrically with [U-(13)C(6)]arginine, [U-(13)C(5)]glutamine, or [U-(13)C(5)]proline during the fasted and fed periods. [ureido-(15)N]citrulline and [(2)H(2)]ornithine were infused intravenously for the entire infusion protocol. During fasting, plasma proline (13%) and ornithine (19%) were the main precursors for citrulline synthesis, whereas plasma arginine (62%) was the main precursor for plasma ornithine. During feeding, enteral (27%) and plasma (12%) proline were the main precursors for the ornithine utilized in the synthesis of citrulline, together with plasma ornithine (27%). Enteral proline and glutamine were utilized directly by the gut to produce ornithine utilized for citrulline synthesis. Arginine was not utilized by the gut, which is consistent with the lack of arginase activity in the neonate. Arginine, however, was the main source (47%) of plasma ornithine and in this way contributed to citrulline synthesis. In conclusion, during the neonatal period, the de novo pathway is the predominant source for the ornithine utilized in the synthesis of citrulline, and proline is the preferred precursor.
瓜氨酸是一种在肠道中合成的氨基酸，用于合成条件必需氨基酸精氨酸。最近，用于瓜氨酸合成的鸟氨酸的来源成为了讨论的话题。多个生理因素可能导致不同研究人员之间的差异；其中之一是研究对象的发育阶段。为了验证在新生儿期从头合成是瓜氨酸合成中鸟氨酸的主要来源的假设，在禁食和喂养期间，通过静脉内或胃内输注[U-(13)C(6)]精氨酸、[U-(13)C(5)]谷氨酰胺或[U-(13)C(5)]脯氨酸，对新生仔猪进行了实验。在整个输注方案中，通过静脉内输注[ureido-(15)N]瓜氨酸和[(2)H(2)]鸟氨酸。在禁食期间，血浆脯氨酸（13%）和鸟氨酸（19%）是瓜氨酸合成的主要前体，而血浆精氨酸（62%）是血浆鸟氨酸的主要前体。在喂养期间，肠内（27%）和血浆（12%）脯氨酸以及血浆鸟氨酸（27%）是用于合成瓜氨酸的鸟氨酸的主要前体。肠内脯氨酸和谷氨酰胺被肠道直接利用来产生用于瓜氨酸合成的鸟氨酸。精氨酸未被肠道利用，这与新生儿缺乏精氨酸酶活性一致。然而，精氨酸是血浆鸟氨酸的主要来源（47%），并以此方式促进瓜氨酸的合成。总之，在新生儿期，从头途径是用于瓜氨酸合成的鸟氨酸的主要来源，脯氨酸是首选前体。
