Glutamine is an important precursor for de novo synthesis of arginine in humans.
BACKGROUND
A metabolic relation exists between glutamine and arginine, 2 amino acids with properties that enhance the recovery of seriously ill patients. It is possible that glutamine exerts part of its beneficial effects by enhancing the availability of arginine.


OBJECTIVE
We aimed to quantify under postabsorptive conditions the metabolic pathway of plasma glutamine into arginine via the intermediate citrulline and to establish the contribution of the kidneys to the synthesis of arginine.


METHODS
The study was conducted in patients during surgery. The metabolism of glutamine, citrulline, and arginine was studied by using intravenous administration of stable isotope tracers of the amino acids. Results were interpreted by using established equations. Parametric tests were used to test and correlate results. P < 0.05 was regarded as significant.


RESULTS
Mean (+/-SE) whole-body plasma turnover rates of glutamine, citrulline, and arginine were 240 +/- 14, 6.2 +/- 0.6, and 42 +/- 2.9 micromol x kg(-1) x h(-1), respectively (P < 0.01). Plasma turnover of citrulline derived from glutamine was shown to be 5.1 +/- 0.7 micromol x kg(-1) x h(-1), and arginine derived from citrulline was shown to be 4.9 +/- 0.9 micromol x kg(-1) x h(-1) (P < 0.01). The contribution of plasma glutamine to plasma arginine derived from plasma citrulline was calculated to be 64%. The kidneys were observed to take up >50% of circulating plasma citrulline and to release equimolar amounts of arginine into plasma.


CONCLUSIONS
This study shows that glutamine is an important precursor for the synthesis of arginine in humans. It also provides a firm basis for future studies exploring the effect of a treatment dose and the route of administration (enteral or parenteral) of glutamine.
Ligthart-Melis
Gerdien C
GC
Department of Surgery, VU University Medical Center, Amsterdam, The Netherlands.
van de Poll
Marcel C G
MC
Boelens
Petra G
PG
Dejong
Cornelis H C
CH
Deutz
Nicolaas E P
NE
van Leeuwen
Paul A M
PA
D000704:Analysis of Variance; D001120:Arginine / Q000096:biosynthesis*; D002247:Carbon Isotopes; D002956:Citrulline / Q000378:metabolism*; D003903:Deuterium; D013505:Digestive System Surgical Procedures; D005260:Female; D005973:Glutamine / Q000008:administration & dosage* / Q000378:metabolism* / Q000493:pharmacokinetics; D006801:Humans; D007262:Infusions, Intravenous; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009587:Nitrogen Isotopes; D010179:Pancreas / Q000378:metabolism
D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D005973:Glutamine; D002956:Citrulline; D001120:Arginine; D003903:Deuterium