AJP - Heart and Circulatory Physiology, Vol 251, Issue 6 1232-H1243, Copyright © 1986 by American Physiological Society
Aminophylline and interstitial adenosine during sustained exercise hyperemia
L. P. Thompson, M. W. Gorman and H. V. Sparks
We tested the hypothesis that an increase in interstitial fluid (ISF)
adenosine concentration contributes to vasodilation of high oxidative
skeletal muscle during sustained free-flow exercise. Canine calf muscles
were stimulated at 3 Hz for 10 min before and after the infusion of the
adenosine receptor antagonist aminophylline (10 mg/kg). The vasodilation
that occurred during aminophylline infusion was allowed to decay before the
postaminophylline exercise period was begun. This dose of aminophylline
shifted the response to infused adenosine 20-fold during rest and reduced
the response to a standard dose by 90% during exercise. Aminophylline had
no significant effect on blood flow or on O2 consumption at rest or during
exercise. Adenosine release (venous minus arterial plasma concentration
times plasma flow) increased during 3-Hz exercise both before and after
aminophylline infusion, but venous plasma adenosine concentration did not
increase in either case. We developed a mathematical model of adenosine
movement between ISF and plasma to help us judge whether to use adenosine
release or venous concentration as an index of ISF adenosine and decided
that venous concentration should be used. We conclude that aminophylline
has no effect on sustained 3-Hz exercise hyperemia because under these
conditions ISF adenosine concentration does not increase.
