AJP - Heart and Circulatory Physiology, Vol 248, Issue 5 678-H687, Copyright © 1985 by American Physiological Society
Arterial blood pressure control during hindlimb and forelimb contraction in the dog
O. Beaty 3rd
This study examined the differential reflex cardiovascular responses evoked
by separate contractions of the right hindlimb and forelimb and established
the mechanism of a regional reflex vasodilation associated with hindlimb
skeletal muscle contraction. The two groups of skeletal muscle were
contracted separately by electrical stimulation (2-48 Hz) of the peripheral
motor nerves. The left nonexercising hindlimb was perfused at constant
flow. All blood pressure-regulating mechanisms were intact. Arterial blood
pressure (ABP), left nonexercising hindlimb perfusion pressure (HLPP), and
heart rate (HR) were recorded. HR was increased by skeletal muscle
contraction. This response was independent of muscle group and contraction
frequency. Increases in both ABP and HLPP were produced by high-frequency
contractions (greater than 16 Hz) of either the hindlimb or forelimb.
Decreases were evoked only by hindlimb contractions (greater than 8 Hz).
The nonexercising skeletal muscle vascular bed contributed to this systemic
depressor response by vasodilating. The mechanism involved a
contraction-induced withdrawal of sympathetic nerve activity to that
vascular bed. Concomitant with this response was an increase in heart rate
that was blocked with propranolol. Similar heart rate changes evoked by
forelimb contractions also were blocked with propranolol. These data
indicate that sympathetic outflow to resting skeletal muscle depends on the
origin and magnitude of the afferent signal from the contracting skeletal
muscle.
