Influence of simulated microgravity on the sympathetic response to
exercise.
Woodman, Christopher R., Kevin. C. Kregel, and Charles M. Tipton.
Department of Veterinary Biomedical Sciences, University of
Missouri, 1600 E. Rollins, Columbia, Missouri 65211
APStracts 3:0339R, 1996.
Rats exposed to simulated conditions of microgravity exhibit
reductions in aerobic exercise capacity which may be due to an
impaired ability of the sympathetic nervous system (SNS) to mediate
an increase in cardiac output and to redistribute blood flow. The
purpose of this study was to quantify the sympathetic response to
exercise in rats following exposure to 14 days of simulated
microgravity or control conditions. To achieve this aim, rats were
exposed to 14 days of head down suspension (HDS) or cage control (CC)
conditions. On day 14, norepinephrine (NE) synthesis was blocked with
[alpha]-methyl-p-tyrosine, and the rate of NE depletion after
synthesis blockade was used to estimate SNS activity in the left
ventricle, spleen and soleus muscle during treadmill exercise at 75%
of maximal oxygen uptake. When compared with CC rats, the sympathetic
response to exercise in HDS rats was characterized by a lower rate of
NE depletion in the left ventricle (-82%) and spleen (-42%). The rate
of NE depletion in the soleus muscle was 47% higher. These
differences could contribute to the decrement in aerobic capacity of
HDS rats by impairing their ability to augment cardiac output and to
redirect blood flow to actively contracting skeletal muscle during
exercise.
Received 7 June 1996; accepted in final form 20 August 1996.
APS Manuscript Number R323-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996