Intrarenal Blood Flow: Microvascular Anatomy and the Regulation of Medullary Perfusion

Pallone, Thomas L.; Silldorff, Erik P.; Turner, M. R.

doi:10.1111/j.1440-1681.1998.tb02220.x

Cited by 99 publications

(113 citation statements)

References 75 publications

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“…A first example is the generation of vasodilatory prostaglandins through activation of cyclooxygenase (COX) (58). It has been observed that perfusion of the renal medulla is sensitive to COX inhibition (110,113,119). Furthermore, renomedullary interstitial cells have receptors for ANG II and BK and release PGE 2 in response to these agents (21, 72,178,179,186).…”

Section: Medullary Po2 and Perfusion Of The Medullamentioning

confidence: 99%

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Physiology of the renal medullary microcirculation

Pallone

Zhang

Rhinehart

2003

American Journal of Physiology-Renal Physiology

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186

193

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Pallone, Thomas L., Zhong Zhang, and Kristie Rhinehart. Physiology of the renal medullary microcirculation. Am J Physiol Renal Physiol 284: F253-F266, 2003; 10.1152/ajprenal.00304.2002.-Perfusion of the renal medulla plays an important role in salt and water balance. Pericytes are smooth muscle-like cells that impart contractile function to descending vasa recta (DVR), the arteriolar segments that supply the medulla with blood flow. DVR contraction by ANG II is mediated by depolarization resulting from an increase in plasma membrane Cl Ϫ conductance that secondarily gates voltage-activated Ca 2ϩ entry. In this respect, DVR may differ from other parts of the efferent microcirculation of the kidney. Elevation of extracellular K ϩ constricts DVR to a lesser degree than ANG II or endothelin-1, implying that other events, in addition to membrane depolarization, are needed to maximize vasoconstriction. DVR endothelial cytoplasmic Ca 2ϩ is increased by bradykinin, a response that is inhibited by ANG II. ANG II inhibition of endothelial Ca 2ϩ signaling might serve to regulate the site of origin of vasodilatory paracrine agents generated in the vicinity of outer medullary vascular bundles. In the hydropenic kidney, DVR plasma equilibrates with the interstitium both by diffusion and through water efflux across aquaporin-1. That process is predicted to optimize urinary concentration by lowering blood flow to the inner medulla. To optimize urea trapping, DVR endothelia express the UT-B facilitated urea transporter. These and other features show that vasa recta have physiological mechanisms specific to their role in the renal medulla. vasa recta; perfusion; hypertension; oxygenation; urinary concentration; patch clamp; calcium; fura 2 THE MICROCIRCULATION OF THE kidney is regionally specialized. In the cortex, afferent and efferent arterioles govern the driving forces that promote glomerular filtration. A dense peritubular capillary plexus arising from efferent arterioles surrounds the proximal and distal convoluted tubules to accommodate enormous reabsorption of glomerular filtrate. In contrast, vasa recta serve needs specific to the medulla. Through the counterflow arrangement of descending (DVR) and ascending vasa recta (AVR), countercurrent exchange traps NaCl and urea deposited to the interstitium by collecting ducts and the loops of Henle. This is vital to maintain corticomedullary osmotic gradients but conflicts with the need to supply nutrient blood flow to medullary tissue. Metabolic substrates that enter the medulla in DVR blood diffuse to the AVR to be shunted back to the cortex. To deal with the threat of medullary hypoxia resulting from this process, the kidney has evolved a capacity to exert subtle control over regional perfusion of the outer and inner medulla. The details are far from clear, but much experimental evidence points to the complex interactions of many autocoids and paracrine agents to modulate vasomotor tone at various sites along the microvascular circuit. The goal of this review is to summarize ...

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Section: Medullary Po2 and Perfusion Of The Medullamentioning

confidence: 99%

“…1). For greater detail, the interested reader is directed to a number of well-illustrated sources (6,7,48,49,55,56,60,81,85,86,99,105,110,113,163).…”

Section: Renal Medullary Microvascular Anatomymentioning

confidence: 99%

Physiology of the renal medullary microcirculation

Pallone

Zhang

Rhinehart

2003

American Journal of Physiology-Renal Physiology

Self Cite

186

193

View full text Add to dashboard Cite

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“…PO 2 is ∼ 70 mm Hg in the cortex, ∼ 20 mm Hg in the outer medulla, and even lower in the inner medulla. Thus, the medulla is in a hypoxic environment under a physiological state [1] . Such an arrangement is strategically necessary to maintain the corticomedullary osmotic gradient for fluid absorption and urine concentration [2] .…”

Section: Kidneys Are Vulnerable To Inflammatory Insultsmentioning

confidence: 99%

“…Such an arrangement is strategically necessary to maintain the corticomedullary osmotic gradient for fluid absorption and urine concentration [2] . To avoid energy deprivation in the low pO 2 regions, an array of hormones, autocoids, and vasoactive substances, mostly synthesized in the medulla, including medullipin, prostaglandins, endothelins, nitric oxide, angiotensin II, kinins, and adenosine are required [1,3] . There is constant and complex interplay among these regulators to optimize regional microvascular blood flow to keep the O 2 supply adequate for tubular consumption.…”

Section: Kidneys Are Vulnerable To Inflammatory Insultsmentioning

confidence: 99%

Inflammation: A Key Contributor to the Genesis and Progression of Chronic Kidney Disease

Qian

2017

Expanded Hemodialysis: Innovative Clinical Approach in Dialysis

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It has become apparent that inflammation and inflammatory reactions can evoke renal injury and promote chronic kidney disease (CKD) progression. Under physiological condition, intrarenal vascular distribution is heterogeneous, and medulla is hypoxic. To avoid energy deprivation in the low pO 2 regions of the kidney, an array of hormones, autocoids, and vasoactive substances, including medullipin, prostaglandins, endothelins, nitric oxide, angiotensin II, kinins, and adenosine, tonically regulates the microvasculature to ensure a perfect match of the microcirculation (O 2 supply) and renal tubules (O 2 demand). Inflammation, systemic or intrarenal, not only can abolish the microvascular response to its regulators, but also induces an array of tubular toxins, including reactive oxygen species, leading to tubular injury, nephron dropout, and onset of CKD. Positive acid balance, electrolyte alterations, and intestinal dysbiosis can perpetuate CKD progression. Understanding the role of inflammation in the genesis and progression of CKD will foster the development of strategies to prevent and treat the underlying inflammation and improve CKD outcomes.

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“…[6][7][8][9][10][11][12] Additionally, FB may entail a greater risk of complications in ECMO patients due to the use of systemic anticoagulation and greater degree of illness in these patients. 13,14 Previous studies have demonstrated the safety of FB in subjects receiving mechanical ventilation. 15,16 However, its safety profile in adult patients supported with ECMO is not well established.…”

Section: Introductionmentioning

confidence: 99%

Flexible Bronchoscopy Is Safe and Effective in Adult Subjects Supported With Extracorporeal Membrane Oxygenation

et al. 2016

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BACKGROUND: Previous studies have demonstrated the safety of flexible bronchoscopy (FB) in mechanically ventilated subjects. However, the safety of FB in adult subjects receiving extracorporeal membrane oxygenation (ECMO) has not been described previously. METHODS: A retrospective review was conducted of all adult subjects who underwent FB while receiving ECMO support at the University of Alabama at Birmingham Hospital from January 1, 2013, to December 31, 2014. Physiologic variables, pre-and post-FB ECMO, and ventilator settings were recorded. RESULTS: 79 adult subjects underwent FB receiving ECMO with a total of 223 bronchoscopies. The most common indications for bronchoscopy included diagnostic evaluation of infection in subjects with pneumonia (29%) and clearance of excessive secretions (22%). In 70% of subjects, moderate or greater amounts of secretions were noted. FB yielded positive culture data in 37 subjects (47%), which resulted in a change to the antibiotic regimen in 14 subjects (38%) with positive culture data. No significant differences in mean P aO 2 /F IO 2 , mean ECMO flow, mean sweep gas, ventilator settings, or hemodynamic parameters (heart rate, oxygen saturation, and mean blood pressure) were noted before and after FB. Complications were mild and transient: blood-tinged secretions after FB in 21% cases, which resolved spontaneously, intraprocedural hypoxemia in 2.2% of cases, and dysrhythmia in <1% of cases. There were no episodes of ECMO cannula dislodgement or inadvertent extubation. CONCLUSIONS: FB can be used safely in adult subjects supported with ECMO and is not associated with significant hemodynamics changes, bleeding, or mechanical complications during ECMO support.

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Intrarenal Blood Flow: Microvascular Anatomy and the Regulation of Medullary Perfusion

Cited by 99 publications

References 75 publications

Physiology of the renal medullary microcirculation

Physiology of the renal medullary microcirculation

Inflammation: A Key Contributor to the Genesis and Progression of Chronic Kidney Disease

Flexible Bronchoscopy Is Safe and Effective in Adult Subjects Supported With Extracorporeal Membrane Oxygenation

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