Production of hydroxyl radicals in contracting skeletal muscle of
cats.
O'neill, Charles A., Charles L. Stebbins, Stefanie Bonigut, Barry
Halliwell, and John C. Longhurst.
Department of Internal Medicine, Division of Cardiovascular
Medicine and Department of Human Physiology, University of
California, Davis, Davis, CA 95616
APStracts 3:0271A, 1996.
Production of reactive oxygen species (ROS) and indices of oxidative
damage appear to increase during exhaustive contraction of skeletal
muscle but characterization of the specific species involved and
their rates of production during nonexhaustive muscle contraction
have not been investigated. Therefore, we tested the hypothesis that
the rate of production of hydroxyl radical (HO x ) increases in
contracting muscle and that this rate is attenuated by pretreatment
with the iron chelator, deferoxamine (DEF), or the nonspecific free
radical scavenger, dimethylthiourea (DMTU). We measured the rate of
production of HO x before, during, and after 5 min of intermittent
static contraction of the triceps surae muscles in cats (n=6). As an
index of HO x production, we assessed formation of p-, m- and o
-tyrosines by hydroxylation of phenylalanine. L-Phenylalanine (30
mg/kg, intravenous, [iv]) was administered to each animal 3 min
before contraction. Blood samples were collected from the popliteal
vein 1 min before contraction; 1, 3 and 4.5 min during contraction;
and 1 min after contraction. During and following contraction, the
cumulative rates of production of p-, m- and o-tyrosines were
elevated by 42.84+/-5.41, 0.25+/-0.04 and 0.21+/-0.03 nmol x min-1 x
g-1, respectively, compared to production in noncontracting triceps
surae muscles. All tyrosines began to increase during early exercise,
before the onset of fatigue. The highest rate of production of
tyrosines was at 4.5 min of contraction and returned toward
precontraction control levels by 1 min after contraction.
Pretreatment with DEF (10 mg/kg, iv, n=5) decreased the cumulative
rates of production of p-, m- and o-tyrosines during and after
contraction by 54+/-8, 22+/-4 and 46+/-7% of control values,
respectively. Similarly, pretreatment with DMTU (10 mg/kg, iv, n=4)
attenuated the cumulative rates of production of p-, m- and o
-tyrosines during and after contraction to 57+/-8, 49+/-11 and 38+/
-7%, respectively. Additionally, D-phenylalanine was administered in a
group of seven animals following the same protocol. The cumulative
rates of production of p-, m- and o-tyrosines increased by 2.25+/
-0.36, 0.29+/-0.05 and 0.26+/-0.02 nmol x min-1 x g-1, respectively.
Finally, the rate of production of tyrosines increased in proportion
to the percentage of maximal tension developed by the triceps surae
muscles. These results directly demonstrate that HO x is produced in
vivo in the skeletal muscle of cats during intermittent static
contraction and that this production can occur before the onset of
fatigue.
Received 23 October 1995; accepted in final form 3 June 1996.
APS Manuscript Number A1140-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96