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Received May 1, 2003
Revised June 10, 2003
Accepted after revision July 29, 2003
1 Yale University
2 Yale University School of Medicine
* To whom correspondence should be addressed. E-mail: sssegal{at}jbpierce.org.
Ascending vasodilatation is integral to blood flow
control in exercising skeletal muscle and is
attributable to conduction from intramuscular arterioles
into proximal feed arteries. Passive stretch of
skeletal muscle can impair muscle blood flow but the
mechanism is not well understood. We hypothesized that
the conduction of vasodilatation along feed arteries can
be modulated by changes in muscle length. In
anaesthetised hamsters, acetylcholine (ACh)
microiontophoresis triggered conducted vasodilatation
along feed arteries (diameter, 50-70 µm) of the
retractor muscle secured at 100% resting length or
stretched by 30%. At 100% length, ACh evoked local
dilatation (> 30 µm) and this response conducted
rapidly along the feed artery (14±1 µm
dilatation at 1600 µm upstream). During muscle
stretch, feed arteries constricted ~10 µm (P <
0.05)
and local vasodilatation to ACh was maintained while
conducted vasodilatation was reduced by half (P <
0.01). Resting diameter and conduction recovered upon
restoring 100% length. Sympathetic nerve stimulation (4-
8 Hz) produced vasoconstriction and attenuated
conduction in the manner observed during muscle stretch,
as did noradrenaline or phenylephrine (10 nM).
Inhibiting nitric oxide production (N
-Nitro-L-
Arginine, 50 µM) produced similar
vasoconstriction
yet had no effect on conduction. Phentolamine,
prazosin, or tetrodotoxin (1 µM) during muscle
stretch abolished vasoconstriction and restored
conduction. Inactivation of sensory nerves with
capsaicin had no effect on vasomotor responses. Thus,
muscle stretch can attenuate conducted vasodilatation by
activating
-adrenoreceptors on feed arteries
through noradrenaline released from perivascular
sympathetic nerves. This autonomic feedback mechanism
will restrict muscle blood flow during passive stretch.
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