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Division of Cardiovascular Medicine, Department of Internal Medicine, University of California, Davis, California 95616
I
investigated whether muscular contraction evokes cardiorespiratory
increases (exercise pressor reflex) in 
-chloralose- and chloral
hydrate-anesthetized and precollicular, midcollicular, and
postcollicular decerebrated rats. Mean arterial pressure (MAP), heart
rate (HR), and minute ventilation (
E) were recorded
before and during 1-min sciatic nerve stimulation, which induced static contraction of the triceps surae muscles, and during 1-min stretch of
the calcaneal tendon, which selectively stimulated mechanosensitive receptors in the muscles. Anesthetized rats showed various patterns of
MAP response to both stimuli, i.e., biphasic, depressor, pressor, and
no response. Sciatic nerve stimulation to muscle in precollicular decerebrated rats always evoked spontaneous running, so the exercise pressor reflex was not determined from these preparations. None of the
postcollicular decerebrated rats showed a MAP response or spontaneous
running. Midcollicular decerebrated rats consistently showed biphasic
blood pressure response to both stimulations. The increases in MAP, HR,
and E were related to the tension developed. The
static contractions in midcollicular decerebrated rats (381 ± 65 g developed tension) significantly increased MAP, HR, and
E from 103 ± 12 to 119 ± 24 mmHg, from
386 ± 30 to 406 ± 83 beats/min, and from 122 ± 7 to
133 ± 25 ml/min, respectively. After paralysis, sciatic nerve
stimulation had no effect on MAP, HR, or E. These
results indicate that the midcollicular decerebrated rat can be a model
for the study of the exercise pressor reflex.
mechanosensitive receptors; metabosensitive receptors; mean arterial pressure; static contraction
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