Addition of tyrosyl-arginine to parenteral nutrition is anabolic in unstressed rats

To determine whether the addition of tyrosine and arginine (Arg), as tyrosyl-arginine (TyrArg), to parenteral nutrition (PN) can promote anabolism, rats were assigned to: 1) PN (1.20 MJ · kg body weight [BW]−1 · d−1 and 1.22 gN · kgBW−1 · d−1; PN control group, n = 5), 2) PN plus TyrArg (2.6 mmol · kgBW−1 · d−1; TyrArg group, n = 6), or 3) PN plus Arg (2.6 mmol · kgBW−1 · d−1; Arg group, n = 5). Results from these three groups were compared with an unoperated chow-fed reference group (chow control group, n = 5). The BW gain during PN and the proportion of lipid in the total body after 14 d of PN was greater for the TyrArg group than for the PN group (P < 0.01). Although the differences in weight gain, body water, lipid, and protein between the TyrArg and Arg groups were not significant, the mean weight gain throughout PN was greater in the TyrArg group than in the Arg group. The proportion of protein in the small intestine, colon, and gastrocnemius muscle was greater in the TyrArg and Arg groups than in the PN group (P < 0.01). A distinct requirement for tyrosine has not been demonstrated in this model, and additional studies in stressed animals are required. In contrast, arginine had tissue-specific anabolic activity.