Background and aims: L-Arg is the substrate for nitric oxide, and also for
L-ornithine which, in turn, is the precursor for the synthesis of collagen
and polyamines. By these different metabolic pathways, L-Arg is involved in
the mechanisms of inflammation, tissue repair and fibrosis. Thus, the aim
of this study was to assess the effect of both different amounts of L-Arg s
upplementation and L-Arg-free diets upon colonic inflammatory damage and fi
brosis in experimental colitis.
Methods: Sprague-Dawley rats with trinitrobenzene sulphonic acid (TNBS)-ind
uced colitis received increasing doses of L-Arg (30,100, 500 mg/day), or D-
Arg (500 mg/day). In a second experiment, two L-Arg-free diets (one supplem
ented with L-Gly) were compared to a L-Arg diet. Nitrite/nitrate release in
the lumen of the colon and colonic damage were evaluated. In the first exp
eriment, tissue collagen levels and colonic mucosal proliferation were also
assessed.
Results: In the acute phase of colitis, intracolonic nitrite/nitrate levels
were significantly higher in the 100 and 500 mg supplemented L-Arg groups
than in D-Arg group. However, only rats treated with 500 mg of L-Arg showed
moderately higher inflammatory and fibrosis colonic scores than the D-Arg
treated rats. There was no significant influence of L-Arg-free diets on the
course of TNBS-induced colitis. However, L-Arg diet accelerated weight gai
n both pre- and post-TNBS.
Conclusions: These results suggest that normal amounts of L-Arg in the diet
are not harmful, whereas both absence of L-Arg or supplementation with hig
h doses of this amino acid may be deleterious. In the former this might be
due to a decrease of nitrogen retention in injured rats, whereas in the lat
ter it may result from both nitric oxide-mediated tissue damage and collage
n deposition. (C) 2001 Harcourt Publishers Ltd.