Reflex responses of renal nerve activity during isometric muscle contraction in cats

Abstract

Renal sympathetic nerve activity (RSNA), arterial blood pressure (AP), and heart rate (HR) were measured during isometric muscle contraction of a hindlimb in chloralose-anesthetized cats. In 14 cats RSNA, AP, and HR increased during a 1-min contraction by 45%, 39 mmHg, and 11 beats/min, respectively; however, in three cats there was a brief initial decrease in RSNA followed by an increase. In 11 cats isometric contraction was maintained for 5 min by alternate stimulation of the L7 and S1 ventral roots. In the first 1 min of sustained contraction, there was a positive correlation (gamma = 0.58, P less than 0.005) between RSNA and tension development. Thereafter RSNA remained elevated despite a tension decrease, and there was no significant correlation between these changes. The RSNA response to contraction of both hindlimbs was greater than that to contraction of either hindlimb alone. Passive stretch of the hindlimb muscle significantly increased RSNA. Thus the initial increase in RSNA during sustained contraction is likely due to activation of muscle mechanoreceptors, whereas the later increase is probably caused by activation of the muscle metaboreceptors.

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

“…With respect to the reflex adjustment of the sympathetic nervous system arising from the contracting muscles, static muscle contraction reflexly augments postganglionic sympathetic nerve activities to the heart, kidney, and skeletal muscle within 10 s from the onset of static muscle contraction evoked in anesthetized animals [1][2][3][4]10]. The rapid increase in cardiac sympathetic nerve activity contributes to an acceleration of cardiac rhythm [4], and the increase in renal sympathetic nerve activity contributes to renal vasoconstriction and a reduction in renal blood flow [3].…”

“…Another interesting point is that the increases in MAP and HR were the same in spite of the difference in the response of plasma NEp. Taking the results into consideration, we think it is very likely that some specific organs (such as the heart, the kidney, and the adrenal medulla), but not all organs, are responsible for the cardiovascular responses during passive stretch, because cardiac and renal sympathetic nerve activities as well as plasma Ep are augmented during passive stretch [2][3][4].…”

“…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-591Japanese Journal of Physiology, 51, 591-597, 2001 Key words: norepinephrine, epinephrine, adrenal medulla, adrenal sympathetic nerve activity, mechanical stretch of muscle. …”

The effect of static exercise on renal sympathetic nerve activity in conscious cats.

“…Also, since the increases in RNA and HR at the beginning of exercise appeared without any significant change in AP, they are unlikely to be a reflex initiated by arterial baroreceptors. Therefore, the initial increases in RNA and HR seem to be evoked directly by descending input from higher brain centres (central command) (Mitchell & Schmidt, 1983;Mitchell, 1985Mitchell, , 1990.…”

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.…”