Renal vascular response to static handgrip exercise: sympathetic vs. autoregulatory control

Abstract

Static exercise causes activation of the sympathetic nervous system, which results in increased blood pressure (BP) and renal vascular resistance (RVR). The question arises as to whether renal vasoconstriction that occurs during static exercise is due to sympathetic activation and/or related to a pressure-dependent renal autoregulatory mechanism. To address this issue, we monitored renal blood flow velocity (RBV) responses to two different handgrip (HG) exercise paradigms in 7 kidney transplant recipients (RTX) and 11 age-matched healthy control subjects. Transplanted kidneys are functionally denervated. Beat-by-beat analyses of changes in RBV (observed via duplex ultrasound), BP, and heart rate were performed during HG exercise in all subjects. An index of RVR was calculated as BP/RBV. In protocol 1, fatiguing HG exercise (40% of maximum voluntary contraction) led to significant increases in RVR in both groups. However, at the end of exercise, RVR was more than fourfold higher in control subjects than in the RTX group (88 vs. 20% increase over baseline; interaction, P Ͻ 0.001). In protocol 2, short bouts of HG exercise (15 s) led to significant increases in RVR at higher workloads (50 and 70% of maximum voluntary contraction) in the control subjects (P Ͻ 0.001). RVR did not increase in the RTX group. In conclusion, we observed grossly attenuated renal vasoconstrictor responses to exercise in RTX subjects, in whom transplanted kidneys were considered functionally denervated. Our results suggest that renal vasoconstrictor responses to exercise in conscious humans are mainly dependent on activation of a neural mechanism.kidney; blood flow; autoregulation; handgrip; vasoconstriction; transplant DURING EXERCISE, THE SYMPATHETIC nervous system is activated, and this results in increases in heart rate (HR), blood pressure (BP), and peripheral vasoconstriction. As part of this process, renal vasoconstriction occurs and serves to maintain BP as well as to redistribute blood flow to the contracting skeletal muscle bed.Of note, the observed increase in renal vascular resistance (RVR) is associated with an increase in arterial pressure. Thus the question arises as to whether renal vasoconstriction that occurs during static exercise is due to sympathetic activation and/or related to a pressure-dependent renal autoregulatory mechanism. To address this issue, we monitored renal hemodynamic responses during two different handgrip exercise paradigms in a group of kidney transplant recipients (RTX) and in age-matched healthy control subjects. Previous reports (7,8,16) suggest that transplanted kidneys remain functionally denervated for several months after transplantation. In studies measuring tissue norepinephrine in rat kidney grafts (7), researchers found grossly diminished norepinephrine levels compared with native kidneys 9 mo after transplantation. Similarly, necropsy specimens from human renal allografts demonstrate a reduction in sympathetic ganglia synaptic density 3 yr after transplantation (16). In addition, the resea...

Renal Hemodynamics and Renal Function After Catheter-Based Renal Sympathetic Denervation in Patients With Resistant Hypertension

“…4 Catheter-based renal denervation (RD) has been introduced into clinical practice to selectively denervate efferent and afferent renal sympathetic fibers.…”

“…1 There is a linear correlation between blood pressure levels and loss in glomerular filtration rate. 2 Doppler sonographic renal resistive index (RRI) reflects systemic and renal hemodynamics, arterial compliance, and pulse pressure 3,4 and has been associated with progression of renal impairment, as well as morbidity and mortality in hypertensive patients. 5 Increased sympathetic tone is an important factor related to the progression of renal disease.…”

“…[6][7][8] Activation of the sympathetic nervous system induces renal vasoconstriction and renin release and increases sodium retention. 4 Catheter-based renal denervation (RD) has been introduced into clinical practice to selectively denervate efferent and afferent renal sympathetic fibers. [9][10][11] Other than marked and sustained blood pressure reductions, RD has also been shown to reduce renal norepinephrine spillover 9 and muscle sympathetic nerve activity 11 and to improve glucose metabolism in patients with resistant hypertension.…”

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“…The autoregulation of renal blood flow, which is caused by the myogenic response and tubule glomerular feedback, enables the kidney to maintain solute and water regulation independent of wide fluctuations of arterial blood pressure. 4 However, because transplanted kidneys were already considered functionally denervated and ischemic, the autoregulation is at a certain degree impaired. Therefore, mean arterial pressure is very important in oxygenation and acidosis and subsequently renal function postoperatively.…”

Electro-Acupuncture at Jianshi (Pc5) and Neiguan (Pc6) Alters Heart Rate Variability (Hrv) in Frightened Volunteers

“…It was systematically described by Charles (Borkovec and O'Brien, 1977), Lerner (Momen et al, 2005), and Etzel (Etzel et al, 2006) have reported an increase in heart rate (HR) during fear. HR changes are in response to the activation or suppression of the cardiac autonomic nervous system (ANS), which is synergistically mediated by the cardiac sympathetic and parasympathetic systems (Guo and Zhang, 2007).…”