The giraffe kidney tolerates high arterial blood pressure by high renal interstitial pressure and low glomerular filtration rate

• Published in: Acta Physiologica Vol. 214; no. 4; pp. 497 - 510
• Main Authors: Damkjær, M., Wang, T., Brøndum, E., Østergaard, K. H., Baandrup, U., Hørlyck, A., Hasenkam, J. M., Smerup, M., Funder, J., Marcussen, N., Danielsen, C. C., Bertelsen, M. F., Grøndahl, C., Pedersen, M., Agger, P., Candy, G., Aalkjær, C., Bie, P.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01-08-2015; Wiley Subscription Services, Inc
• Subjects: Animals; Arterial Pressure - physiology; blood pressure; Female; Giraffes - physiology; glomerular filtration; Glomerular Filtration Rate; Hemodynamics - physiology; interstitial hydrostatic pressure; Kidney - blood supply; Kidney - physiology; Male; renal plasma flow; renin; blood pressure; glomerular filtration; interstitial hydrostatic pressure; renin; renal plasma flow
• ISSN: 1748-1708; 1748-1716
• DOI: 10.1111/apha.12531

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.
Conclusion
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.