title: Two-compartment model of inner medullary vasculature supports dual modes of vasopressin-regulated inner medullary blood flow.
abstract: The outer zone of the renal inner medulla (IM) is spatially partitioned into two distinct interstitial compartments in the transverse dimension. In one compartment (the intercluster region), collecting ducts (CDs) are absent and vascular bundles are present. Ascending vasa recta (AVR) that lie within and ascend through the intercluster region (intercluster AVR are designated AVR(2)) participate with descending vasa recta (DVR) in classic countercurrent exchange. Direct evidence from former studies suggests that vasopressin binds to V1 receptors on smooth muscle-like pericytes that regulate vessel diameter and blood flow rate in DVR in this compartment. In a second transverse compartment (the intracluster region), DVR are absent and CDs and AVR are present. Many AVR of the intracluster compartment exhibit multiple branching, with formation of many short interconnecting segments (intracluster AVR are designated AVR(1)). AVR(1) are linked together and connect intercluster DVR to AVR(2) by way of sparse networks. Vasopressin V2 receptors regulate multiple fluid and solute transport pathways in CDs in the intracluster compartment. Reabsorbate from IMCDs, ascending thin limbs, and prebend segments passes into AVR(1) and is conveyed either upward toward DVR and AVR(2) of the intercluster region, or is retained within the intracluster region and is conveyed toward higher levels of the intracluster region. Thus variable rates of fluid reabsorption by CDs potentially lead to variable blood flow rates in either compartment. Net flow between the two transverse compartments would be dependent on the degree of structural and functional coupling between intracluster vessels and intercluster vessels. In the outermost IM, AVR(1) pass directly from the IM to the outer medulla, bypassing vascular bundles, the primary blood outflow route. Therefore, two defined vascular pathways exist for fluid outflow from the IM. Compartmental partitioning of V1 and V2 receptors may underlie vasopressin-regulated functional compartmentation of IM blood flow.
authors.affiliation: Department of Physiology, University of Arizona Health Sciences Center, Tucson, Arizona 85724-5051, USA.
authors.forename: Julie
authors.initials: J
authors.lastname: Kim
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Pannabecker
mesh_terms: D000818:Animals; D003198:Computer Simulation; D004730:Endothelium, Vascular / Q000378:metabolism; D007090:Image Interpretation, Computer-Assisted; D007150:Immunohistochemistry; D007671:Kidney Concentrating Ability; D007679:Kidney Medulla / Q000098:blood supply*; D008297:Male; D008833:Microcirculation; D008856:Microscopy, Fluorescence; D008953:Models, Anatomic; D008955:Models, Cardiovascular; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D020286:Pericytes / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017483:Receptors, Vasopressin / Q000378:metabolism; D012079:Renal Circulation; D014508:Urea / Q000378:metabolism; D014667:Vasopressins / Q000378:metabolism*
chemical_list: D017483:Receptors, Vasopressin; D014667:Vasopressins; D014508:Urea
references.citation: Physiol Rev. 1996 Apr;76(2):425-536
references.pmid: 8618962
references.citation: Am J Physiol Renal Physiol. 2002 Mar;282(3):F530-40
references.pmid: 11832436
references.citation: Am J Physiol Renal Physiol. 2008 Dec;295(6):F1744-51
references.pmid: 18842821
references.citation: J Am Soc Nephrol. 1992 Jun;2(12):1677-88
references.pmid: 1498275
references.citation: Kidney Int. 1974 Dec;6(6):379-87
references.pmid: 4444142
references.citation: J Anat. 1963 Oct;97:543-53
references.pmid: 14064096
references.citation: Am J Physiol Renal Physiol. 2007 Sep;293(3):F696-704
references.pmid: 17609288
references.citation: Am J Physiol. 1981 Jul;241(1):R3-16
references.pmid: 7018270
references.citation: Z Zellforsch Mikrosk Anat. 1964 Oct 23;64:381-403
references.pmid: 14320463
references.citation: Am J Physiol Renal Physiol. 2008 Jun;294(6):F1306-14
references.pmid: 18417543
references.citation: Am J Physiol. 1997 Nov;273(5):R1742-8
references.pmid: 9374818
references.citation: Am J Physiol Regul Integr Comp Physiol. 2003 May;284(5):R1153-75
references.pmid: 12676741
references.citation: Am J Physiol Renal Physiol. 2000 Jan;278(1):F52-62
references.pmid: 10644655
references.citation: Am J Physiol Renal Physiol. 2010 Jul;299(1):F265-72
references.pmid: 20392798
references.citation: Pflugers Arch. 1988 Jul;412(1-2):42-53
references.pmid: 3174386
references.citation: Am J Physiol Renal Physiol. 2006 Jun;290(6):F1355-66
references.pmid: 16380456
references.citation: Physiol Rev. 2002 Jan;82(1):205-44
references.pmid: 11773613
references.citation: Am J Physiol Renal Physiol. 2008 Nov;295(5):F1271-85
references.pmid: 18495796
references.citation: J Clin Invest. 1985 Aug;76(2):770-8
references.pmid: 4031072
references.citation: Am J Physiol. 1976 Aug;231(2):313-8
references.pmid: 961881
references.citation: Am J Physiol Renal Physiol. 2003 Dec;285(6):F1210-24
references.pmid: 12952854
references.citation: Am J Physiol. 1987 Sep;253(3 Pt 2):F576-81
references.pmid: 2957929
references.citation: Exp Physiol. 2000 Mar;85 Spec No:223S-231S
references.pmid: 10795926
references.citation: Am J Physiol. 1993 Mar;264(3 Pt 2):R578-83
references.pmid: 8457011
references.citation: Am J Physiol. 1997 Jul;273(1 Pt 2):R1-15
references.pmid: 9249526
references.citation: Am J Physiol. 1987 Nov;253(5 Pt 2):F823-32
references.pmid: 3688238
references.citation: Kidney Int. 1987 Feb;31(2):641-7
references.pmid: 3550235
references.citation: Am J Physiol Renal Physiol. 2010 Apr;298(4):F973-87
references.pmid: 20053796
references.citation: Am J Physiol Renal Physiol. 2004 Oct;287(4):F816-39
references.pmid: 15213067