Adaptation to a long term (4 WKS) arginine-precursor-free diet in adult humans

To evaluate the adaptive mechanisms of arginine (arg) homeostasis in vivo to an arginine-precursor-free intake (APF), we conducted an experiment in 4 healthy adults given an arginine-glutamate-proline-aspartate-free diet for 4 weeks preceded by one week at adequate amino acid and energy intake. Three additional subjects received an isonitrogenous control adequate diet for 5 weeks. All subjects received four 24h (12h fast; 12h fed) intravenous infusions, L[guanidino-¹⁵N₂,5,5,²H₂ arginine, L[¹³C]leucine and ¹³C urea on days 4 and 32; and L[5-¹³C]arginine and L[ureido-¹³C,5,5,²H₂]citrulline were given on day s 7 and 35. Plasma arginine fast fluxes decreased during APF from 73±5 to 41±2; in controls values were 76±2 and 78±0.6 μmol.kg.h, respectively, for fast and fed periods. Arg synthesis (cit->arg) was not different between dietary groups (12±2 vs 9±0.1 μ.mol kg.h; APF vs control). However, arg oxidation at 4 weeks was 22.8±6.8 for controls and 8.1±3 μmol.kg. for APF. Therefore, long-term adaptation to an APF intake is achieved by sustained decreased rates of arg oxidation, without increased synthesis.