Journal of Applied Physiology, Vol 64, Issue 4 1493-1499, Copyright © 1988 by American Physiological Society
Effects of naloxone on systemic and regional hemodynamic responses to exercise in dogs
N. Imai, C. K. Stone, P. D. Woolf and C. S. Liang
Department of Medicine, University of Rochester Medical Center, New York 14642.
To determine whether endogenous opiates have a role in circulatory
regulation during mild to moderate exercise, 11 chronically instrumented
dogs were exercised on a treadmill up a 6% incline at 2.5 and 5.0 mph, each
for 20 min, after treatment with either the opiate receptor antagonist
naloxone (1 mg/kg bolus and 20 micrograms.kg-1.min-1 infusion) or normal
saline. Naloxone increased plasma beta-endorphin and adrenocorticotropic
hormone at rest but had no effect on resting heart rate, aortic pressure,
cardiac output, left ventricular time derivative of pressure (dP/dt) and
ratio of dP/dt at a developed pressure of 50 mmHg and the developed
pressure (dP/dt/P), or plasma catecholamines. Plasma beta-endorphin and
adrenocorticotropic hormone increased during exercise. In addition, graded
treadmill exercise produced proportional increases in heart rate, cardiac
output, aortic pressure, left ventricular dP/dt and dP/dt/P, and blood flow
to exercising muscles, right and left ventricular myocardium, and adrenal
glands. However, there were no differences in the circulatory responses to
exercise between animals receiving naloxone and normal saline. Thus the
endogenous opiate system probably does not play an important role in
regulating the systemic hemodynamic and blood flow responses to mild and
moderate exercise.
