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Alpha-adrenergic-mediated
reflex responses to induced muscular contraction are changed with age in
dogs
G C Haidet Abstract
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Abstract
Aging significantly affects reflex cardiovascular (CV) responses to induced
muscular contraction in anesthetized dogs. To further investigate whether
age-related changes in alpha-adrenergic-mediated responses to muscular
contraction contribute to these previously reported age-related changes in CV
responses associated with advanced age, hemodynamic and regional blood flow
(BF) responses at baseline and during hindlimb contraction (HLC) were
evaluated both before and after alpha-blockade (alpha-AB) in older (8-14 yr
old) and in younger (2-3 yr old) beagles during alpha-chloralose anesthesia.
alpha-AB with phentolamine resulted in significant (P < 0.05) reductions in
mean arterial pressure before and during HLC, regardless of age. However,
age-related differences in the systemic vascular resistance, cardiac output,
and stroke volume responses to HLC, observed before alpha-AB, were eliminated
after phentolamine as the result of an age-related difference in each of these
responses to alpha-AB. Baseline BF (microspheres) was unchanged after alpha-AB
in seven of eight abdominal organs, regardless of age. However, reductions in
BF during HLC were attenuated in seven of eight abdominal organs in the
younger dogs after alpha-AB, but in none of these organs in the older dogs,
indicative of diminished alpha-mediated vasoconstriction in these organs in
the older dogs during HLC. Furthermore, the age-related difference in the
combined BF reduction to all eight abdominal organs before alpha-AB was
eliminated after alpha-AB. Finally, BF increases to two of four contracting
muscles, as well as the combined increase in blood flow to all four
contracting muscles, were attenuated after alpha-AB, regardless of age. These
results demonstrate that alpha-blockade eliminates many of the age-related
differences in CV responses to HLC observed before alpha-AB and suggest that
alpha-adrenergic-mediated responses to HLC change with age in beagles.
Reference
AMERICAN JOURNAL OF PHYSIOLOGY , 265(6 Pt
2):H1899-H1908 1993
Updated January 2016
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