title: Autoregulation of renal medullary blood flow in rabbits.
abstract: We examined the extent of renal medullary blood flow (MBF) autoregulation in pentobarbital-anesthetized rabbits. Two methods for altering renal arterial pressure (RAP) were compared: the conventional method of graded suprarenal aortic occlusion and an extracorporeal circuit that allows RAP to be increased above systemic arterial pressure. Changes in MBF were estimated by laser-Doppler flowmetry, which appears to predominantly reflect erythrocyte velocity, rather than flow, in the kidney. We compared responses using a dual-fiber needle probe held in place by a micromanipulator, with responses from a single-fiber probe anchored to the renal capsule, to test whether RAP-induced changes in kidney volume confound medullary laser-Doppler flux (MLDF) measurements. MLDF responses were similar for both probe types and both methods for altering RAP. MLDF changed little as RAP was altered from 50 to >or=170 mmHg (24 +/- 22% change). Within the same RAP range, RBF increased by 296 +/- 48%. Urine flow and sodium excretion also increased with increasing RAP. Thus pressure diuresis/natriuresis proceeds in the absence of measurable increases in medullary erythrocyte velocity estimated by laser-Doppler flowmetry. These data do not, however, exclude the possibility that MBF is increased with increasing RAP in this model, because vasa recta recruitment may occur.
authors.affiliation: Department of Physiology, Monash University, Melbourne, Australia. gabriela.eppel@med.monash.edu.au
authors.forename: Gabriela A
authors.initials: GA
authors.lastname: Eppel
authors.forename: Goran
authors.initials: G
authors.lastname: Bergstrom
authors.forename: Warwick P
authors.initials: WP
authors.lastname: Anderson
authors.forename: Roger G
authors.initials: RG
authors.lastname: Evans
mesh_terms: D000758:Anesthesia; D000818:Animals; D004231:Diuresis; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006706:Homeostasis; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000098:blood supply* / Q000502:physiology; D017078:Laser-Doppler Flowmetry; D008297:Male; D009318:Natriuresis; D010477:Perfusion; D011817:Rabbits; D012077:Renal Artery / Q000502:physiology; D012079:Renal Circulation / Q000502:physiology*; D012964:Sodium / Q000652:urine
chemical_list: D012964:Sodium