Goodman
MN
Proc Soc Exp Biol Med 1994; 205:182-5
In
previous studies, interleukin-1 (IL-1) or tumor necrosis factor (TNF) have been
demonstrated to augment skeletal muscle protein breakdown in a manner similar
to that induced by bacterial endotoxin. This response to IL-1 or TNF was elicited
only after they were administered to animals for various periods, as their addition
in vitro to incubated muscles from normal untreated rats was without effect. This
suggested that IL-1 and TNF may augment muscle proteolysis in an indirect fashion.
Serum levels of IL-1, TNF as well as interleukin-6 (IL-6) are all elevated during
infection induced by bacterial endotoxin. Both IL-1 and TNF can induce the synthesis
of IL-6 by a variety of cells. Because of this, in the present report, the ability
of IL-6 to stimulate skeletal muscle protein breakdown was examined. Muscle protein
breakdown was evaluated by measuring the release of both tyrosine and 3-methylhistidine
by incubated muscles. Pretreatment of rats with IL-6 for 6 hr induced fever and
increased the release of both tyrosine and 3-methylhistidine by the extensor digitorum
longus muscle. However, IL-6 did not augment muscle proteolysis when muscles from
normal untreated rats were incubated in the presence of the cytokine. The data
suggest that the acute treatment of animals with IL-6 can augment muscle proteolysis.
Whether this response is due to a direct effect of IL-6 on the myocyte or whether
it is due to the production of other mediators remains unclear. |
