Journal of Applied Physiology, Vol 65, Issue 2 625-632, Copyright © 1988 by American Physiological Society
Endurance training in dogs increases vascular responsiveness to an alpha 1-agonist
Y. M. Evans, J. N. Funk, J. B. Charles, D. C. Randall and C. F. Knapp
Biomedical Engineering Center, Wenner-Gren Laboratory, University of Kentucky, Lexington 40506.
The effects of endurance training on vascular responsiveness to an alpha
1-agonist and the associated changes in baroreflex modulation of heart rate
and vascular resistance were studied. Graded dosages of phenylephrine were
given to eight treadmill-trained dogs and to eight untrained dogs; both
groups were chronically instrumented and were sedated and resting when
tested. These dosages were repeated after ganglionic blockade. Aortic
pressure, cardiac output, central venous pressure, peripheral resistance,
and heart rate were each averaged over 30 s before injection and 90 s after
injection. The slope of the peripheral resistance-dose relationship was
significantly increased in trained compared with untrained dogs in both the
unblocked and blocked cases [unblocked: trained 0.89, untrained 0.47;
blocked: trained 4.30, untrained 2.05 (mmHg.l-1.min)/(microgram.kg-1)]. The
unblocked resistance slopes were reduced with respect to the blocked slopes
by 77 (untrained) and 79% (trained). The slope of the heart rate-aortic
pressure response was reduced, but not significantly, by endurance
training. We conclude that 6 wk of endurance training in dogs resulted in a
doubling of the vascular responsiveness to an alpha 1-agonist, with no
significant change in the baroreflex regulation of resistance or heart
rate.
