The effects
of adrenalectomy and autonomic blockades on the tachycardia at the beginning of
dynamic exercise in conscious rats
Rie Wakasugi,
Tomoko Nakamoto, and Kanji Matsukawa
Department of
Physiology, Graduate
Heart rate (HR) during dynamic
exercise is controlled not only by cardiac sympathetic and parasympathetic
outflows but also by plasma catecholamines. To clarify their contribution to the
exercise-induced tachycardia, we examined the effects of adrenalectomy (ADX)
and autonomic blockades on HR at the beginning of treadmill exercise (10 m/min
for 30 s) in 13 conscious rats.
Baseline HR did not differ between intact and ADX rats [367 ± 3 (mean ±
SE) vs. 350 ± 11 beats/min], suggesting no significant role of adrenal
catecholamines on the baseline HR.
The initial increase in HR at the beginning of exercise (0-10 s from the
exercise onset), which was more blunted by atenolol than atropine methyl
nitrate, was the same
between the intact and ADX conditions (80 ± 8 vs. 77 ± 8 beats/min). During the later period of exercise
(10-30 s) in the intact condition, there was a further increase in HR of 14
beats/min, which was blunted by ADX.
Thus it is likely that the initial tachycardia at the beginning of
dynamic exercise is predominantly produced by the cardiac autonomic mechanism,
especially a prompt increase in CSNA rather than a decrease in CVNA, and that the
hormonal mechanism due to adrenal catecholamines contributes to an increase in
HR during the later period of exercise.
Key word: adrenalectomy,
autonomic blockades, exercise-induced tachycardia