title: The giraffe kidney tolerates high arterial blood pressure by high renal interstitial pressure and low glomerular filtration rate.
abstract: BACKGROUND
  The tallest animal on earth, the giraffe (Giraffa camelopardalis) is endowed with a mean arterial blood pressure (MAP) twice that of other mammals. The kidneys reside at heart level and show no sign of hypertension-related damage. We hypothesized that a species-specific evolutionary adaption in the giraffe kidney allows normal for size renal haemodynamics and glomerular filtration rate (GFR) despite a MAP double that of other mammals.
  
  
  METHODS
  Fourteen anaesthetized giraffes were instrumented with vascular and bladder catheters to measure glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). Renal interstitial hydrostatic pressure (RIHP) was assessed by inserting a needle into the medullary parenchyma. Doppler ultrasound measurements provided renal artery resistive index (RI). Hormone concentrations as well as biomechanical, structural and histological characteristics of vascular and renal tissues were determined.
  
  
  RESULTS
  GFR averaged 342 ± 99 mL min(-1) and ERPF 1252 ± 305 mL min(-1) . RIHP varied between 45 and 140 mmHg. Renal pelvic pressure was 39 ± 2 mmHg and renal venous pressure 32 ± 4 mmHg. A valve-like structure at the junction of the renal and vena cava generated a pressure drop of 12 ± 2 mmHg. RI was 0.27. The renal capsule was durable with a calculated burst pressure of 600 mmHg. Plasma renin and AngII were 2.6 ± 0.5 mIU L(-1) and 9.1 ± 1.5 pg mL(-1) respectively.
  
  
  CONCLUSIONS
  In giraffes, GFR, ERPF and RI appear much lower than expected based on body mass. A strong renal capsule supports a RIHP, which is >10-fold that of other mammals effectively reducing the net filtration pressure and protecting against the high MAP.
authors.affiliation: Department of Cardiovascular and Renal Research, University of Southern Denmark, Odense, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Damkjaer
authors.affiliation: Department of Biological Sciences, Institute of Zoophysiology, Aarhus University, Aarhus, Denmark.
authors.forename: T
authors.initials: T
authors.lastname: Wang
authors.affiliation: Department of Physiology, Institute of Biomedicine, Aarhus University, Aarhus, Denmark.
authors.forename: E
authors.initials: E
authors.lastname: Brøndum
authors.affiliation: Centre for Clinical Research, Hjørring/Department of Clinical Medicine, Aalborg University, Denmark.
authors.forename: K H
authors.initials: KH
authors.lastname: Østergaard
authors.affiliation: Centre for Clinical Research, Hjørring/Department of Clinical Medicine, Aalborg University, Denmark.
authors.forename: U
authors.initials: U
authors.lastname: Baandrup
authors.affiliation: Department of Radiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Hørlyck
authors.affiliation: Department of Cardiothoracic and Vascular Surgery, Institute of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: J M
authors.initials: JM
authors.lastname: Hasenkam
authors.affiliation: Department of Cardiothoracic and Vascular Surgery, Institute of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Smerup
authors.affiliation: Department of Cardiothoracic and Vascular Surgery, Institute of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Funder
authors.affiliation: Department of Clinical Pathology, University of Southern Denmark, Odense, Denmark.
authors.forename: N
authors.initials: N
authors.lastname: Marcussen
authors.affiliation: Department of Anatomy, Institute of Biomedicine, Aarhus University, Aarhus, Denmark.
authors.forename: C C
authors.initials: CC
authors.lastname: Danielsen
authors.affiliation: Center for Zoo and Wild Animal Health, Copenhagen Zoo, Copenhagen, Denmark.
authors.forename: M F
authors.initials: MF
authors.lastname: Bertelsen
authors.affiliation: Center for Zoo and Wild Animal Health, Copenhagen Zoo, Copenhagen, Denmark.
authors.forename: C
authors.initials: C
authors.lastname: Grøndahl
authors.affiliation: MR Research Centre, Institute of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Pedersen
authors.affiliation: MR Research Centre, Institute of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: P
authors.initials: P
authors.lastname: Agger
authors.affiliation: Department of Physiology and Medicine, University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: G
authors.initials: G
authors.lastname: Candy
authors.affiliation: Department of Physiology, Institute of Biomedicine, Aarhus University, Aarhus, Denmark.|Department of Biomedicine, University of Copenhagen, Copenhagen, Denmark.
authors.forename: C
authors.initials: C
authors.lastname: Aalkjaer
authors.affiliation: Department of Cardiovascular and Renal Research, University of Southern Denmark, Odense, Denmark.
authors.forename: P
authors.initials: P
authors.lastname: Bie
mesh_terms: D000818:Animals; D062186:Arterial Pressure / Q000502:physiology*; D005260:Female; D000068276:Giraffes / Q000502:physiology*; D005919:Glomerular Filtration Rate; D006439:Hemodynamics / Q000502:physiology*; D007668:Kidney / Q000098:blood supply / Q000502:physiology*; D008297:Male
keywords: blood pressure; glomerular filtration; interstitial hydrostatic pressure; renal plasma flow; renin