Relationships between muscle membrane lipids, fiber type and enzyme
activities in sedentary and exercised rats.
Kriketos, A. D., D. A. Pan, J. R. Sutton, J. F. Y. Hoh, L. A. Baur, G.
J. Cooney, A. B. Jenkins, L. H. Storlien.
Department of Endocrinology, Royal Prince Alfred Hospital, Sydney
NSW 2050, Departments of Medicine, Biomedical Science and Physiology,
University of Sydney, Sydney NSW 2006 and Department of Biomedical
Science, University of Wollongong, Wollongong NSW 2522
APStracts 2:0184R, 1995.
Insulin resistance in skeletal muscle is associated with: 1) relative
increases in the proportion of glycolytic, fast-twitch muscle fibers
and decreases in the proportion of more oxidative fibers; and 2) a
higher proportion of the saturated fatty acids in membrane structural
lipids. Exercise is known to improve insulin action. The aim of the
current studies were: 1) to investigate the relationship between
muscle fiber type and membrane fatty acid composition; and 2) to
determine how voluntary exercise might influence both variables. In
sedentary Wistar rats in experiment 1, increased amounts of
unsaturated fatty acids were found in the more oxidative, insulin
-sensitive red quadriceps (RQ) and soleus muscles, while reduced
levels of polyunsaturated fatty acids were found in primarily
glycolytic white quadriceps (WQ) muscles. In experiment 2, voluntary
running wheel exercise by adult female rats over 45 days resulted in
reduced proportions of type 2b fibers (p = 0.01) and increased
proportions of type 2a/2x fibers (p = 0.03) in extensor digitorum
longus (EDL) muscle. The magnitude of these changes were related to
the distance run (r = -0.73, p = 0.04; r = 0.79, p = 0.02,
respectively). Exercise significantly increased oxidative capacity,
assessed by the proportion of NADH intense stained fibers (p =
0.0004), citrate synthase (p = 0.003) and hexokinase (p = 0.04)
activities. Citrate synthase activity was also increased by exercise
in soleus muscle, where, as expected, no fiber type changes were
detected. No significant differences in the fatty acid profile of
soleus and EDL were found between groups. Voluntary exercise may play
a role in improving insulin sensitivity through beneficial
alterations in muscle fiber type and oxidative capacity. Membrane
fatty acid composition can be improved by diet but appears unaffected
by moderate exercise. Taken together these results suggest that diet
and exercise may improve insulin action through separate and
synergistic mechanisms.
Received 27 December 1994; accepted in final form 13 June 1995.
APS Manuscript Number R734-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.