Isolated interstitial nodal spaces may facilitate preferential solute and fluid mixing in the rat renal inner medulla

Gilbert, Rebecca L.; Pannabecker, Thomas L.

doi:10.1152/ajprenal.00539.2011

Cited by 16 publications

(11 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our preliminary studies also indicate that rodent and human inner medullary architecture share fundamental similarities. Finally, we have developed several mathematical models to determine how these physiologic and structural features might relate to the concentrating mechanism (24,(46)(47)(48). In this paper, we briefly review some of the main findings and put them into context with regard to the concentrating mechanism.…”

Section: Introductionmentioning

confidence: 99%

Urine-Concentrating Mechanism in the Inner Medulla

Dantzler

Layton

et al. 2014

Clinical Journal of the American Society of Nephrology

Self Cite

View full text Add to dashboard Cite

SummaryThe ability of mammals to produce urine hyperosmotic to plasma requires the generation of a gradient of increasing osmolality along the medulla from the corticomedullary junction to the papilla tip. Countercurrent multiplication apparently establishes this gradient in the outer medulla, where there is substantial transepithelial reabsorption of NaCl from the water-impermeable thick ascending limbs of the loops of Henle. However, this process does not establish the much steeper osmotic gradient in the inner medulla, where there are no thick ascending limbs of the loops of Henle and the water-impermeable ascending thin limbs lack active transepithelial transport of NaCl or any other solute. The mechanism generating the osmotic gradient in the inner medulla remains an unsolved mystery, although it is generally considered to involve countercurrent flows in the tubules and vessels. A possible role for the three-dimensional interactions between these inner medullary tubules and vessels in the concentrating process is suggested by creation of physiologic models that depict the threedimensional relationships of tubules and vessels and their solute and water permeabilities in rat kidneys and by creation of mathematical models based on biologic phenomena. The current mathematical model, which incorporates experimentally determined or estimated solute and water flows through clearly defined tubular and interstitial compartments, predicts a urine osmolality in good agreement with that observed in moderately antidiuretic rats. The current model provides substantially better predictions than previous models; however, the current model still fails to predict urine osmolalities of maximally concentrating rats.

show abstract

Section: Introductionmentioning

confidence: 99%

Urine-Concentrating Mechanism in the Inner Medulla

Dantzler

Layton

et al. 2014

Clinical Journal of the American Society of Nephrology

Self Cite

View full text Add to dashboard Cite

show abstract

“…A mathematical model of fluid and solute flows through an INS predicted that the mixing of NaCl and urea, reabsorbed from ATLs and CDs, could generate hyperosmotic interstitial fluid compared with CD tubular fluid (11). We observed a high degree of abutment between the AVR and INS (ϳ19% of total INS circumference) for both the Munich-Wistar rat and kangaroo rat.…”

Section: Discussionmentioning

confidence: 74%

Architecture of interstitial nodal spaces in the rodent renal inner medulla

Gilbert

Pannabecker

2013

American Journal of Physiology-Renal Physiology

Self Cite

View full text Add to dashboard Cite

Every collecting duct (CD) of the rat inner medulla is uniformly surrounded by about four abutting ascending vasa recta (AVR) running parallel to it. One or two ascending thin limbs (ATLs) lie between and parallel to each abutting AVR pair, opposite the CD. These structures form boundaries of axially running interstitial compartments. Viewed in transverse sections, these compartments appear as four interstitial nodal spaces (INSs) positioned symmetrically around each CD. The axially running compartments are segmented by interstitial cells spaced at regular intervals. The pairing of ATLs and CDs bounded by an abundant supply of AVR carrying reabsorbed water, NaCl, and urea make a strong argument that the mixing of NaCl and urea within the INSs and countercurrent flows play a critical role in generating the inner medullary osmotic gradient. The results of this study fully support that hypothesis. We quantified interactions of all structures comprising INSs along the corticopapillary axis for two rodent species, the Munich-Wistar rat and the kangaroo rat. The results showed remarkable similarities in the configurations of INSs, suggesting that the structural arrangement of INSs is a highly conserved architecture that plays a fundamental role in renal function. The number density of INSs along the corticopapillary axis directly correlated with a loop population that declines exponentially with distance below the outer medullary-inner medullary boundary. The axial configurations were consistent with discrete association between near-bend loop segments and INSs and with upper loop segments lying distant from INSs.

show abstract

“…Mathematical simulations support an important role for interstitial nodal spaces in generating the inner medullary osmotic gradient of the Munich-Wistar rat (11). Their existence provides compelling structural evidence for preferential NaCl reabsorption into an interstitial compartment that preferentially drives fluid reabsorption from water-permeable CDs.…”

Section: Discussionmentioning

confidence: 77%

“…Kangaroo rats have longer water-permeable DTLs and shorter NaCl-permeable prebend segments than those of Munich-Wistar rat (36), an architecture that potentially supports a steeper driving force for NaCl reabsorption into interstitial nodal spaces in the former species and a higher urine concentrating ability (24). Also, the proportions of ATLs and AVR that form the interstitial nodal spaces along the inner medullary axis may be relevant to understanding their fluid and solute flows within solute mixing and countercurrent systems (11). Finally, plasma vasopressin titer of kangaroo rat exceeds that of Sprague-Dawley rat in hydrated or dehydrated animals (34), so there is reason to hypothesize that vasopressin regulation of kangaroo rat tubular function differs from that of the laboratory rat.…”

Section: Perspectives and Significancementioning

confidence: 99%

Architecture of vasa recta in the renal inner medulla of the desert rodent Dipodomys merriami: potential impact on the urine concentrating mechanism

Issaian

Urity

Dantzler

et al. 2012

American Journal of Physiology-Regulatory, Integrative and Comp

Self Cite

View full text Add to dashboard Cite

Issaian T, Urity VB, Dantzler WH, Pannabecker TL. Architecture of vasa recta in the renal inner medulla of the desert rodent Dipodomys merriami: potential impact on the urine concentrating mechanism. Am J Physiol Regul Integr Comp Physiol 303: R748 -R756, 2012. First published August 22, 2012; doi:10.1152/ajpregu.00300.2012.-We hypothesize that the inner medulla of the kangaroo rat Dipodomys merriami, a desert rodent that concentrates its urine to over 6,000 mosmol/kg H2O, provides unique examples of architectural features necessary for production of highly concentrated urine. To investigate this architecture, inner medullary vascular segments in the outer inner medulla were assessed with immunofluorescence and digital reconstructions from tissue sections. Descending vasa recta (DVR) expressing the urea transporter UT-B and the water channel aquaporin 1 lie at the periphery of groups of collecting ducts (CDs) that coalesce in their descent through the inner medulla. Ascending vasa recta (AVR) lie inside and outside groups of CDs. DVR peel away from vascular bundles at a uniform rate as they descend the inner medulla, and feed into networks of AVR that are associated with organized clusters of CDs. These AVR form interstitial nodal spaces, with each space composed of a single CD, two AVR, and one or more ascending thin limbs or prebend segments, an architecture that may lead to solute compartmentation and fluid fluxes essential to the urine concentrating mechanism. Although we have identified several apparent differences, the tubulovascular architecture of the kangaroo rat inner medulla is remarkably similar to that of the Munich Wistar rat at the level of our analyses. More detailed studies are required for identifying interspecies functional differences. urea transport; UT-B; aquaporin; concentrating mechanism DURING THE PAST TWO DECADES the three-dimensional architecture of the rat renal medulla has become increasingly pertinent to development of advanced computational models of medullary function (5,12,13,15,37,38). Recent advances have been made in understanding the geometrical relationships of collecting ducts (CDs) and nephrons of the outer medulla and inner medulla (28, 40 -42). However, much remains to be learned about compartmentation arising from dynamic flow of fluid and solutes between these structures; compartmentation that is essential for understanding the role of the renal medulla in processes of urine concentration and sodium and water balance (6, 23). For each of these processes, blood flow through medullary vasculature is highly integrated with epithelial fluid and solute fluxes, and more complete understanding of vessel architecture and connectivity between descending vasa recta (DVR) and ascending vasa recta (AVR) will more clearly define this compartmentation. The classical studies of the kangaroo rat (33) and other desert species demonstrating tolerance to low water intake underscore the potential insights these species could offer in understanding vascular compartmentation (1, 2) and its ...

show abstract

Isolated interstitial nodal spaces may facilitate preferential solute and fluid mixing in the rat renal inner medulla

Cited by 16 publications

References 42 publications

Urine-Concentrating Mechanism in the Inner Medulla

Urine-Concentrating Mechanism in the Inner Medulla

Architecture of interstitial nodal spaces in the rodent renal inner medulla

Architecture of vasa recta in the renal inner medulla of the desert rodent Dipodomys merriami: potential impact on the urine concentrating mechanism

Contact Info

Product

Resources

About