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Received May 17, 2004
Revised June 15, 2004
Accepted after revision September 14, 2004
1 Yale University School of Medicine & John B. Pierce Laboratory
* To whom correspondence should be addressed. E-mail: sssegal{at}jbpierce.org.
Physical work capacity diminishes with ageing, but little
is known of how the microvascular supply to skeletal
muscle fibers is affected. To test the hypothesis that
ageing alters blood flow control, we investigated network
architecture and vasomotor responses of arterioles in the
gluteus maximus muscle of Young (2-3 mo), Adult (12-14
mo), and Old (18-20 mo) C57BL6 male mice (n = 83).
Microvascular casts revealed that the total number,
length, and surface area of arteriolar segments
(diameter, 10-50 µm) were not significantly different
across age-groups. However, for arterioles with diameter
30 µm, tortuosity and branch angles increased
with age (P < 0.05). In anesthetized mice, second-
order (2A) distributing arterioles had similar resting
(17 ± 1 µm) and maximal (37 ± 1 µ
m) diameters and similar responsiveness to cumulative
(10-10-10-4 M) superfusion of
acetylcholine or phenylephrine. With superfusate oxygen
raised from 0 to 21%, 2A constriction in Young (11 &
[plusmn] 1 µm) was greater (P < 0.05) than Adult
and Old (5 ± 1 µm). Observed 1 mm upstream
from ACh microiontophoresis (1 µA, 1 s), conducted
vasodilatation was 10 ± 1 µm in Young, 17 &
[plusmn] 1 µm in Adult and 6 ± 1 µm in
Old (P < 0.05). With muscle contractions (2, 4, and
8 Hz; 30 s) arteriolar diameter increased similarly
across age-groups (6 ± 1, 11 ± 1, and 18 &
[plusmn] 1 µm, respectively). Muscle mass and active
tension were similar across age-groups yet post-
contraction vasodilatation recovered more rapidly in Old
vs. Adult and Young (P < 0.05). With arteriolar
network architecture maintained during ageing, the
impairment in conducted vasodilatation and attenuation of
post-contraction vasodilatation may compromise exercise
tolerance.
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