AJP - Heart and Circulatory Physiology, Vol 243, Issue 2 196-H206, Copyright © 1982 by American Physiological Society
Active and passive capillary control in red muscle at rest and in exercise
C. R. Honig, C. L. Odoroff and J. L. Frierson
Capillary control was quantified in dog gracilis muscles from in situ.
About 550 capillaries/mm2, one-third the total number present, were
perfused with erythrocytes simultaneously at rest; two-thirds the total
could be perfused during maximal vasodilation. The functional capillary
reserve was about 600/mm2. Capillary distribution at rest reflects a
passive, random process at individual capillaries and an active process
that coordinates perfusion of small groups of capillaries. The latter
creates long diffusion distances. These are unaltered by denervation, or
flow per se, but are abolished by adenosine. Twitch contraction at 4/min
recruited about 400 capillaries/mm2 without any change in flow. Capillaries
opened selectively where diffusion distances were longest. The same changes
occurred within 5 s during work at 4/s, even if flow was held constant. If
flow could increase, about 200 additional capillaries/mm2 were slowly
recruited, without change in capillary distribution. Conclusions are that
1) hemodynamics and active vasomotion contribute equally to capillary
density at rest; 2) active papillary control in exercise is ungraded and
solely responsible for eliminating metabolically significant diffusion
paths; 3) flow and capillary density can be controlled independently by
proximal and terminal arterioles, respectively.
