Plasma arginine kinetics in adult man: Response to an arginine-free diet

Adaptation to a long term (4weeks) arginine- and precursor (glutamate, proline and aspartate)-free diet

“…There were marked differences (P > 0.05) in plasma amino acid concentrations for the fed and fasted state as previously observed. 8,11 In contrast to the plasma concentrations of arginine, ornithine, proline, glutamate, aspartate and leucine which decreased during the fasted state, when adequate intake was given, plasma citrulline was higher (P > 0.05) during the fasted state at 1 and 4 weeks for the control and APF groups, and this is also consistent with previous data. 15 There was a significant effect of the 4-week APF diet on plasma amino acid concentrations.…”

“…The lowest arginine concentrations were observed when the APF diet had been consumed for 4 weeks (P < 0.001), but interestingly the lowest concentration was observed during the fed period. Plasma citrulline values were similar to those previously reported in healthy subjects, 11,15 and did not change with the 4-week APF intake. Plasma leucine concentrations were variable.…”

“…Nevertheless, in qualitative terms, the response to a 4-week APF restriction appears to be similar to that following a 1-week restriction of dietary arginine alone. 11,15 Thus, a reduced rate of arginine oxidation with maintenance of endogenous arginine synthesis, which occurs at a rate of about one-third of the dietary intake level, supports the notion 12 that arginine homeostasis is maintained initially via modulations in the rate of arginine oxidation, via conversion to ornithine and subsequently to glutamate. Whether this response requires a change in the levels/activities of arginase isoenzymes 22,23 and/or of ornithine aminotransferase 22 and/ or whether it is a consequence of the lower concentrations of arginine in the plasma, reflecting smaller intracellular pools, cannot be determined from the present study.…”

“…There was a difference (P = 0.001) in plasma arginine fluxes, regardless of the tracer used, for the fast and fed state, as previously observed. 11,15 However, there was no difference in plasma arginine fluxes between weeks 1 and 4 of the control group. In the APF group receiving adequate intake during week 1, there was a difference (P < 0.001) in plasma arginine fluxes between fed and fasted state.…”

“…Previously, we have studied the changes in whole body arginine metabolism over a shorter, 6-day arginine-free diet and observed that (i) arginine fluxes were reduced, especially during the fed period, (ii) net arginine synthesis was not influenced by an acute change in arginine intake, (iii) the rate of conversion of arginine to ornithine was markedly reduced, as was the rate of arginine oxidation, especially in the fed state. 11,12,15 In the present study we extended the period of dietary restriction to 4 weeks, including limiting the intakes of the major, immediate dietary precursors of arginine (proline, glutamate, and aspartate). Nevertheless, in qualitative terms, the response to a 4-week APF restriction appears to be similar to that following a 1-week restriction of dietary arginine alone.…”