Static muscular contraction elicits a pressor reflex in the
chicken.
Solomon, Irene C., and Thomas P. Adamson.
Division of Cardiovascular Medicine and Section of Neurobiology,
Physiology, and Behavior, University of California, Davis, CA
95616
APStracts 3:0350R, 1996.
Static muscular contraction has been shown to increase arterial blood
pressure and heart rate in humans and other mammals. It is not clear,
however, whether or not birds exhibit a similar response to this
maneuver. Therefore, we designed these experiments to determine if
the chicken exhibits a cardiovascular response to static muscular
contraction, and if the observed responses are evoked through a
reflex involving muscle afferents. Static contraction of the
gastrocnemius muscle was evoked by electrically stimulating the
sciatic nerve at 1.5-3.0 times motor threshold (30-40 Hz; 0.025 ms)
in 13 chloralose-anesthetized cockerels. We measured arterial blood
pressure and muscle tension before and during static contraction, and
calculated mean arterial pressure and heart rate from the arterial
pressure trace. We found that static contraction of the gastrocnemius
muscle increased mean arterial pressure from 71 +/- 4 to 95 +/- 4
mmHg (P < 0.05) and increased heart rate from 304 +/- 8 to 345
+/- 10 bpm (P < 0.05). Further, we found that stimulation of the
sciatic nerve following paralysis of the birds with vecuronium
bromide or stimulation of the cut peripheral end of the sciatic nerve
(using the same stimulation parameters described above) evoked no
change in mean arterial pressure or heart rate. We conclude that
static muscular contraction of the gastrocnemius muscle in the
chicken elicits a pressor response, and that this response is due to
a reflex arising from the contracting muscles.
Received 2 May 1996; accepted in final form 4 September 1996.
APS Manuscript Number R245-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996