Stimulation of renal sympathetic activity by static contraction: evidence for mechanoreceptor-induced reflexes from skeletal muscle.

Abstract

Static muscular contraction in anesthetized animals has been firmly established to reflexly increase arterial pressure. Although group III and IV muscle afferents are known to be responsible for this reflex pressor response, there is no evidence that the stimulation of muscle mechanoreceptors, many of which are supplied by group III fibers, plays a role in causing this contraction-induced reflex effect. To provide this evidence, we recorded renal sympathetic nerve activity in chloralose-anesthetized cats while contracting the triceps surae muscles. We found that static contraction tripled renal nerve activity within three seconds of its onset, an increase that was abolished by cutting the L6 and S2 dorsal roots. On average, the contraction-induced increase in renal nerve activity was observed 0.8 +/- 0.1 seconds after the onset of this maneuver. In addition, intermittent tetanic contractions synchronized renal nerve discharge so that a burst of activity was evoked by each contraction. A similarly synchronized renal nerve discharge was evoked in paralyzed cats by electrical stimulation of the tibial nerve at five times motor threshold, a current intensity that activates group III afferents. We conclude that, in anesthetized animal preparations, mechanoreceptors with group III afferents contribute to the reflex stimulation of renal sympathetic outflow evoked by muscular contraction.

Reflex Responses in Plasma Catecholamines Caused by Static Contraction of Skeletal Muscle.

“…Since the passive mechanical stretch of muscle in a physiological range can stimulate myelinated group III afferents rather than unmyelinated group IV afferents, a comparison in the reflex responses of sympathetic efferent nerve activity between the contraction and the mechanical stretch of skeletal muscle should lead to an insight into the afferent mechanisms in the contracting muscle. The mechanical stretch of muscle increases cardiac and renal sympathetic nerve activities to 85 and 51% of their responses observed during static contraction with the same tension development [1,3]. Regarding AdSNA, it increased immediately after the onset of static muscle contraction in anesthetized rats [5].…”

“…It was demonstrated that sympathetic outflows to the heart and the kidneys increase during static muscle contraction induced by electrical stimulation of the ventral roots in anesthetized cats [1][2][3][4]. The increase in cardiac sympathetic nerve activity correlates with an increase in heart rate [3], and the increase in renal sympathetic nerve activity correlates with reduced renal blood flow [2], suggesting that the reflex changes in postganglionic sympathetic nerve activities caused by skeletal muscle contraction contribute to cardiovascular adjustments, such as increases in cardiac output and arterial blood pressure and a redistribution of car-…”

Exaggerated Renal Vasoconstriction During Exercise in Heart Failure Patients

“…In animals, the mechanoreflex has been shown to modulate the renal vascular bed. 22,23 For example, in chloralose-anesthetized cats, mechanical stimulation of the triceps surae muscle produces an immediate reflex increase in efferent renal sympathetic nerve activity. 22 In normal humans, we have reported that central command and/or mechanoreceptors help mediate reflex renal vasoconstriction during static handgrip exercise.…”

“…22,23 For example, in chloralose-anesthetized cats, mechanical stimulation of the triceps surae muscle produces an immediate reflex increase in efferent renal sympathetic nerve activity. 22 In normal humans, we have reported that central command and/or mechanoreceptors help mediate reflex renal vasoconstriction during static handgrip exercise. 1 We have previously reported that at the onset of low-intensity exercise, before the generation of ischemic metabolites, there was significant reflex renal vasoconstriction.…”

Exercise pressor reflex in health and diseases: Animal studies

“…1). Sympathetic nerve activities (SNA) directed toward blood vessels in a variety of organs including kidney 36,37) , skeletal muscle 38) , and heart 39) , were increased when hindlimb skeletal muscle was continuously and statically contracted in anesthetized or unanesthetized decerebrate cats. Moreover, the roles played by the EPR-evoked sympathoexcitation in mediating renal vasoconstriction 40) and tachycardia 39) have been demonstrated.…”