Sepsis increases contraction-related generation of reactive oxygen
species in the diaphragm.
Nethery, D., A. Dimarco, D. Stofan, and G. Supinski.
Pulmonary Division, Department of Medicine, Case Western Reserve
University and Metrohealth Medical Center, Cleveland, Ohio
APStracts 6:0256A, 1999.
Recent work indicates that free radicals mediate sepsis-induced
diaphragmatic dysfunction (14,16,17,22). These previous experiments
have not, however, established the source of the responsible free
radical species. In theory, this phenomenon could be explained if one
postulates that sepsis elicits an upregulation of contraction-related
free radical formation in muscle. The purpose of the present study
was to test this hypothesis by examining the effect of sepsis on
contraction-related free radical generation (i.e., formation of
reactive oxygen species, ROS) by the diaphragm. Rats were killed 18
hr after injection with either saline or endotoxin. In vitro
hemidiaphragms were then prepared and ROS generation during
electrically induced contractions (20 Hz trains delivered for 10 min)
was assessed by measuring the conversion of hydroethidine to
ethidium. We found that ROS generation was negligible in
noncontracting diaphragms from both saline and endotoxin treated
groups (2.0 + 0.6 ng ethidium/mg tissue and 2.8 + 1.0 ng/mg,
respectively), but was marked in contracting diaphragms from saline
-treated animals (19.0 + 2.8 ng/mg) and even more pronounced (30.0 +
2.8 ng/mg) in diaphragms from septic animals (P<0.01). This
enhanced free radical generation occurred despite the fact that the
force-time integral (i.e. the area under the curve of force vs. time)
for control diaphragms was higher than for the septic group. In
additional studies, in which we altered the stimulation paradigm in
control muscles to achieve a force-time integral similar to that
achieved in septic muscles, an even greater difference between
control and septic muscle ROS formation was observed. These data
indicate that ROS formation during contraction is markedly enhanced
in diaphragms from endotoxin-treated, septic animals. We speculate
that ROS generated in this fashion plays a central role in producing
sepsis-related skeletal muscle dysfunction.
Received 15 July 1998; accepted in final form 1 June 1999.
APS Manuscript Number A642-8.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 14 June 1999