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标题：The Food Energy/Protein Ratio Regulates the Rat Urea Cycle but Not Total Nitrogen Losses
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作者：Laia Oliva ; Marià Alemany ; Xavier Remesar 等
期刊名称：Nutrients
电子版ISSN：2072-6643
出版年度：2019
卷号：11
期号：2
页码：316-327
DOI：10.3390/nu11020316
出版社：MDPI Publishing
摘要：Nitrogen balance studies have shown that a portion of the N ingested but not excreted is not accounted for. We compared several diets (standard, high-fat, high-protein, and self-selected cafeteria) to determine how diet-dependent energy sources affect nitrogen handling, i.e., the liver urea cycle. Diet components and rat homogenates were used for nitrogen, lipid, and energy analyses. Plasma urea and individual amino acids, as well as liver urea cycle enzyme activities, were determined. Despite ample differences in N intake, circulating amino acids remained practically unchanged in contrast to marked changes in plasma urea. The finding of significant correlations between circulating urea and arginine-succinate synthase and lyase activities supported their regulatory role of urea synthesis, the main N excretion pathway. The cycle operation also correlated with the food protein/energy ratio, in contraposition to total nitrogen losses and estimated balance essentially independent of dietary energy load. The different regulation mechanisms observed have potentially important nutritional consequences, hinting at nitrogen disposal mechanisms able to eliminate excess nitrogen under conditions of high availability of both energy and proteins. Their operation reduces urea synthesis to allow for a safe (albeit unknown) mechanism of N/energy excess accommodation.
关键词：urea cycle; nitrogen balance; protein/energy ratio; rat urea cycle ; nitrogen balance ; protein/energy ratio ; rat