Journal of Applied Physiology, Vol 53, Issue 3 665-670, Copyright © 1982 by American Physiological Society
Modification of training-induced responses by repeated norepinephrine injections in rats
M. Harri, P. Kuusela and R. Oksanen-Rossi
Rats were subjected to daily (5 times/wk) running exercises, norepinephrine
injections (0.5 mg/kg sc), or both for 9 wk; one rat group served as the
control. Norepinephrine injections were used to potentiate the effect of
the endogenous amine, the release of which is known to be stimulated by
exercise. Changes observable in all treated rat groups included reduced
weight gain, reduced food intake, decreased amount of epididymal fat,
hypertrophy of the heart and adrenals, and increased tail skin temperature
response to isoproterenol (0.2 mg/kg sc). The training-specific changes
(increased activity of oxidative muscle enzymes) were not potentiated by
training under the influence of exogenous norepinephrine administration.
The changes produced by repeated norepinephrine injections alone
(hypertrophy of the brown adipose tissue and increased colonic temperature
response to isoproterenol) failed to develop if the rats underwent physical
training in addition to drug treatment. Lower tail skin temperature in a
cool environment (15 degrees C) was associated with norepinephrine
treatment, whether or not there was simultaneous training. These results
suggest that the chronic norepinephrine treatment-physical training
combination led to complex adaptive changes that could not be
systematically associated with either norepinephrine treatment or physical
training alone.
