AJP - Heart and Circulatory Physiology, Vol 246, Issue 5 690-H695, Copyright © 1984 by American Physiological Society
Decreased uptake of exogenous substrates following graded muscle stimulation
P. M. Walker, D. A. Mickle, W. R. Tanner, R. Harding and A. D. Romaschin
An exercising in vivo canine hindlimb model was used to assess the pattern
of exogenous substrate delivery and uptake as a function of contraction
frequency. The limb was stimulated to contract at 0, 4, 8, 12 8, 4, and 0
Hz for 10-min periods. Blood flow was proportional to stimulatory
frequency. Oxygen consumption increased to a maximum at 12 Hz and
subsequently declined. Glucose, free fatty acid, and lactate uptakes
decreased despite increased deliveries and maintained arterial
concentrations at 12 Hz. At this point there was a net release of glycerol
and lactate from the muscle. Microvascular shunting was not the cause of
decreased exogenous substrate uptake at 12 Hz. A switch from exogenous to
endogenous muscle substrates occurred with the onset of decreased substrate
uptake. The mechanism that facilitates this switch from exogenous to
endogenous substrates remains unknown.
