Wutzke K D, Heine W, Plath C, Müller M, Uhlemann M
Department of Medicine, Children's Hospital, University of Rostock, Germany.
Pediatr Res. 1992 Feb;31(2):95-101. doi: 10.1203/00006450-199202000-00001.
[15N]glycine, [15N]leucine, and [15N]yeast protein thermitase hydrolysate (YPTH) as tracers for investigating the protein turnover rates in premature infants were studied in nine human milk-fed neonates (born after 32 to 34 wk of gestation) by paired comparison of the tracers. The 15N enrichment of total urinary nitrogen and ammonia after administration of a single oral dose of 15N was measured by emission spectrometry. Flux rates were calculated using a three-compartment model and the ammonia end product method. The mean whole-body protein synthesis rates, as determined by the three-compartment model derived from the three 15N tracers, differed significantly (p less than 0.01) among [15N]glycine (15.9 g/kg/d), [15N] leucine (9.1 g/kg/d), and 15N-YPTH (5.9 g/kg/d). When the corresponding rates were determined from the excretion of label in ammonia, the results showed the opposite tendency; the lowest apparent synthesis rates were found after [15N]glycine (7.5 g/kg/d), followed by [15N]leucine (14.4 g/kg/d), and the highest figure resulted after [15N] YPTH (16.7 g/kg/d). The results of this comparison substantiate the assumption that there are methodologic errors in connection with the use of different tracers and models for the calculation of whole-body protein parameters in preterm infants, with respect to the main requirement for tracer kinetic studies; the tracer nitrogen must be representative of total amino acid nitrogen. Seen in this light, mixtures of completely labeled amino acids such as YPTH may represent the most reliable tracer substance.(ABSTRACT TRUNCATED AT 250 WORDS)
在9名母乳喂养的新生儿（妊娠32至34周后出生）中，通过对示踪剂的配对比较，研究了[15N]甘氨酸、[15N]亮氨酸和[15N]酵母蛋白热解产物（YPTH）作为研究早产儿蛋白质周转率的示踪剂。单次口服15N后，通过发射光谱法测量总尿氮和氨中的15N富集情况。通量率使用三室模型和氨终产物法进行计算。由三种15N示踪剂推导的三室模型确定的平均全身蛋白质合成率在[15N]甘氨酸（15.9 g/kg/d）、[15N]亮氨酸（9.1 g/kg/d）和15N-YPTH（5.9 g/kg/d）之间存在显著差异（p<0.01）。当根据氨中标记物的排泄确定相应速率时，结果显示出相反的趋势；[15N]甘氨酸后表观合成率最低（7.5 g/kg/d），其次是[15N]亮氨酸（14.4 g/kg/d），[15N]YPTH后最高（16.7 g/kg/d）。这种比较结果证实了这样一种假设，即就示踪剂动力学研究的主要要求而言，在使用不同示踪剂和模型计算早产儿全身蛋白质参数时存在方法学误差；示踪剂氮必须代表总氨基酸氮。从这个角度来看，完全标记的氨基酸混合物如YPTH可能是最可靠的示踪物质。（摘要截断于250字）
