AJP - Heart and Circulatory Physiology, Vol 248, Issue 5 688-H694, Copyright © 1985 by American Physiological Society
Carotid sinus and blood pressure control during hindlimb and forelimb contractions
O. Beaty 3rd
Arterial blood pressure (ABP) regulation during exercise involves in part
medullary interaction of afferent information from contracting skeletal
muscles and the major baroreceptors. This study examined in
chloralose-anesthetized dogs the role of the carotid sinus baroreceptors in
modulating reflex changes in ABP, nonexercising hindlimb skeletal muscle
vascular resistance, and heart rate (HR) evoked by two separately
contracting (4, 16, and 48 Hz) groups of skeletal muscle, the right
hindlimb and forelimb. When arterial and cardiopulmonary baroreceptor
afferent information was interrupted, hindlimb contractions evoked a
greater augmentation of ABP (16 and 48 Hz) and no further increase in
nonexercising hindlimb perfusion pressure (HLPP). Forelimb contractions,
which in the presence of baroreceptors had not affected ABP (4 and 16 Hz),
now reduced it profoundly. Nonexercising HLPP, which increased
independently of contraction frequency, now was decreased by 4 Hz, not
affected by 16 Hz, and increased by 48 Hz. The increase in HR was
abolished. Increasing carotid sinus pressure to 220 mmHg in vagotomized
dogs abolished the reflex changes evoked by hindlimb skeletal muscle
contractions. However, forelimb contractions continued to decrease ABP.
Nonexercising HLPP and HR did not change from the precontraction values.
These data indicate that the carotid sinus baroreceptor could buffer
completely those changes in the selected cardiovascular variables evoked by
hindlimb but not forelimb skeletal muscle contractions. Thus the role of
the carotid sinus baroreceptors in controlling ABP during exercise depends
on the group of skeletal muscle initiating the somatic afferent signal and
its influence on the contraction-induced distribution of the efferent
signals.
