Optimal levels of arginine in maintenance intravenous hyperalimentation

The optimal levels of arginine (Arg) for growth and immunity were studied in mildly depleted, noninjured rats maintained on intravenous hyperalimentation. Three groups of S-D rats (eight/group, weighing 275-300 g) underwent catheter insertion, 1 day of fasting, and then 7 days of intravenous hyperalimentation consisting of 20% dextrose, adequate minerals and vitamins, and three amino acid regimens: (1) FreAmine II (1.55 g Arg/liter); (2) FreAmine III (4.05 g Arg/liter); (3) experimental (7.5 g Arg/liter). The increase in arginine levels was achieved by lowering the glycine levels. There were no differences among the groups in terms of body weight gain (6.9 vs 8.3 vs 10.0 g) or in cumulative N balance (574 vs 660 vs 642 mg). Liver, spleen, and adrenal weights did not differ. Thymus weight was greater in groups B and C: (A) 345 ± 27 mg vs (B) 445 ± 34 mg, p < 0.05, vs (C) 438 ± 26 mg, p < 0.05) as were the total number of lymphocytes/thymus (x10^-9) (A) 0.93 ± 0.12 vs (B) 1.37 ± 0.18, p < 0.05 vs (C) 1.46 ± 0.15, p < 0.05). Mitogen-induced thymocyte blastogenesis (cpm) was greatest in group C in response to phytohemagglutinin: (A) 9,558 ± 3,799 vs (B) 20,088 ± 5,890, NS, vs (C) 37,234 ± 6,209, p < 0.01 vs A and p < 0.05 vs B) and Concanavalin A: (A) 71,035 ± 15,228 vs (B) 111,734 ± 15,021, NS, vs (C) 172,967 ± 19,861, p < 0.01 vs A and p < 0.05 vs B). In the intravenous hyperalimentation-maintained noninjured rat ARG concentrations more than 1.55 g/liter do not enhance N retention or growth. Larger doses of ARG have strong thymic immunostimulatory effects without any toxicity or growth reduction.