K. Tyml et O. Mathieu-costello, Structural and functional changes in the microvasculature of disused skeletal muscle, FRONT BIOSC, 6, 2001, pp. D45-NIL_4
Skeletal muscle and its microvasculature can exhibit remarkable plasticity
in response to decreased functional demand (i.e., muscle disuse). Since the
microvascular adaptation to disuse does seem to not depend solely on reduc
ed demand, this review examines the various factors that may be responsible
for the observed regression of microvascular structure and function during
disuse. There are several animal models of muscle disuse; their common fea
ture is that they are associated with a variety of confounding effects that
make the interpretation of the "pure" disuse effect challenging. As well,
in clinical studies, the effect of disuse can be difficult to separate from
that of various pathologies. Regardless of methodological difficulties, de
generation of the capillary wall, capillary loss, arteriolar remodelling, r
educed resting state blood flow, and reduced arteriolar responsiveness to a
cute vasodilative and vasoconstrictive stimuli have all been observed in di
sused muscles. The level, and presence/absence of these changes may depend
on many factors including the duration of disuse, degree of muscle atrophy,
residual muscle activity, microvascular blood flow, release of vasoactive
agents from the degenerating muscle, muscle type, and the particular pathol
ogy associated with the muscle withering in humans. It is the present chall
enge to discover the presence/absence of key agents (possibly originating a
t the interface between the blood stream and the vascular wall, within the
extracellular matrix, or the muscle fibres themselves) that alter the intra
- and/or inter-cellular signalling to explain the mechanism of adaptation o
f the microvasculature to skeletal muscle disuse.