부산대학교 도서관

Background: Cats are unique among domestic animals in that they are obligate carnivores and have a high protein requirement. However, there are few data on protein turnover and amino acid (AA) metabolism in cats. Objective: The aim of this study was to examine the effects of dietary protein content on urea production and Leu metabolism in cats. Methods: Eighteen neutered male cats (4.4 [+ or -] 0.11 kg body weight, aged 4.6 [+ or -] 0.41 y) fed to maintain body weight for 3 wk with 15%, 40%, or 65% metabolizable energy intake as crude protein (CP) had [1-[sup.13]C]Leu administered in the fed state. Urea production was measured by the infusion of [[sup.15][N.sub.2]]urea. Leu flux, nonoxidative Leu disposal (NOLD; protein synthesis), Leu rate of appearance ([R.sub.a]; protein degradation), and Leu oxidation were determined. Results: Urea production and Leu oxidation were both ~3 times greater in cats fed 65% CP compared with those fed 15% CP, whereas those fed 40% CP were ~1.6 times greater (P < 0.05). Leu flux was 1.9 and 1.3 times greater in cats fed 65% CP compared with those fed 15% and 40% CP (P< 0.001). Almost 39% of total Leu flux was oxidized by cats fed 15% CP, whereas this increased to 58% in cats fed 65% CP (P < 0.002). There were no differences for Ra, but cats fed 65% CP tended to have 30% greater NOLD (P = 0.09) and to be in positive protein balance (P = 0.08) compared with those fed 15% CP. Conclusion: The high protein requirement of cats combined with a low rate of whole-body protein synthesis ensures that an obligate demand of AAs for energy or glucose (or both) can be met in an animal that evolved with a diet high in protein with very little or no carbohydrate. J Nutr 2015;145:2471-8. Keywords: Felis catus, carnivore, protein metabolism, protein turnover, urea, precursor method doi:10.3945/jn.115.216275.