Journal of Applied Physiology, Vol 70, Issue 3 1097-1104, Copyright © 1991 by American Physiological Society
Effects of feeding on muscle blood flow during prolonged exercise in miniature swine
M. D. McKirnan, C. G. Gray and F. C. White
Department of Pathology, University of California, San Diego School of Medicine, La Jolla 92093-0612.
Eight exercise-trained miniature swine were studied during prolonged
treadmill runs (100 min) under fasting and preexercise feeding conditions.
Each animal ran at identical external work loads that corresponded to 65%
of the heart rate reserve (210-220 beats/min) for the two exercise bouts.
Cardiac outputs and stroke volumes were higher and heart rates lower for
fed than for fasting runs (P less than 0.05). Preexercise feeding did not
alter oxygen consumption, core temperature, mean arterial pressure, and
arterial-mixed venous oxygen difference during prolonged exercise; however,
mixed venous lactate concentration was lower at end exercise than during
fasting conditions (1.2 vs. 2.6 mM, P less than 0.05). Microsphere
measurements of regional blood flow revealed significantly higher total
gastrointestinal flow (23%) for fed than for fasting conditions. Throughout
the exercise bout, blood flow to the biceps femoris, semitendinosus, and
tibialis anterior muscles was lower in fed than in fasted animals (P less
than 0.05). Combined hindlimb muscle blood flow averaged 15 ml.min-1.100
g-1 (18%, P less than 0.05) lower under feeding than fasting run
conditions. These findings provide further evidence that cardiovascular
reflexes originate in the gut after feeding to increase cardiac output and
redistribute a portion of the blood flow away from active muscle to the
gastrointestinal tract during prolonged exercise.
