Reflex responses in cardiac parasympathetic and sympathetic nerve activities during passive stretch or electrically-evoked contraction of skeletal muscle

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We measured directly both cardiac vagal efferent nerve activity (CVNA) and cardiac sympathetic efferent nerve activity (CSNA) during passive stretch and static contraction of skeletal muscle in cats decerebrated at the level of the precollicular-premammillary body. CVNA gradually decreased during passive stretch of the hindlimb, which was sustained throughout the stretched during passive stretch of the hindlimb, which was sustained throughout the stretch. CSNA increased at the onset of passive stretch but this increase was not sustained. CVNA and CSNA responded differentially to the passive stretch of the triceps surae muscle as well as the hindlimb. The time course and direction of the cardiac autonomic responses to muscle stretch were not affected by partial sinoaortic denervation, although the magnitude of the CSNA response was augmented. On the other hand, CVNA was decreased during static muscle contraction evoked by electrical stimulation of the tibial nerve and CSNA was increased. These responses in CVNA and CSNA were augmented, as the muscle tension was increased. It is concluded that a reflex arising from skeletal muscle during passive stretch and static contraction contributes to differential regulation of cardiac parasympathetic and sympathetic efferent discharges.