Butyrate seemed to have no effect on the oxidative
stress; however, it clearly increased HomoSer and
HomoCys levels. The former could be a consequence of
a higher transmethylation activity or absorption. In
contrast, trans-sulfuration activity seemed not to be
correspondingly increased since HomoSer was strongly
accumulated. Moreover, it seems that cystathione clyase
might be the responsible enzyme for the limited
trans-sulfuration activity. The reported increase in
digestibility and nitrogen retention in Atlantic salmon
receiving a supplementation of Cys (Nordrum et al.
2000) should be in line with these conclusions.
As a resume, the present work is the first using a
metabolic array to support the positive effect of butyrate
on growth and feed efficiency found in a marine fish,
being the suggested mode of action depicted in Fig. 3.
Although some of the effects demonstrated in other
species were not assessed in the present work (e.g.,
immunostimulation, histological changes in the epithelium),
a detailed evaluation of the metabolic profile of the
intestine, combined with an assessment of the intestinal
microbiota composition, may provide in future experiments
a better insight into the potential beneficial effects
of butyrate on the nutritive metabolism of fish.