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(Circulation. 1996;94:3067-3068.)
© 1996 American Heart Association, Inc.

Articles

A `BOLD' New Approach to Renal Oxygen Economy

Bruce C. Kone, MD

the Department of Internal Medicine and Integrative Biology, the University of Texas Medical School at Houston.

Correspondence to Bruce C. Kone, MD, Division of Renal Diseases and Hypertension, the University of Texas Medical School at Houston, 6431 Fannin, MSB 4.148, Houston, TX 77030. E-mail bkone@heart.med.uth.tmc.edu.

Key Words: Editorials • kidney • oxygen • blood • magnetic resonance imaging • perfusion • circulation

	Introduction

 
The kidney is a remarkable circulatory organ. Despite contributing <0.5% of the total body mass, the kidney commands 25% of the cardiac output and exhibits the highest rates of blood flow per weight of any organ.¹ The architecture and regulatory precision of the renal microcirculation dictate large differences in blood flow among the zones of the renal parenchyma. The bulk of renal blood flow is directed to the cortex to facilitate glomerular filtration and tubular reabsorption of solute and water, whereas blood flow through the hairpin loops of the medullary vasa recta is much slower to preserve osmotic gradients necessary for efficient urinary concentration.² The vasa recta provide nutrients and oxygen to the medullary tubules, abstract metabolic waste from the tubular reabsorbate, and help to maintain medullary interstitial osmotic gradients by acting as countercurrent exchangers. The countercurrent flow of the vasa recta, coupled with the high rates of active solute transport and gradient generation by the medullary thick ascending limb of Henle (mTAL), results in a steep corticomedullary gradient of oxygen, ranging from a PO₂ of 50 mm Hg in the cortex to 10 to 20 mm Hg in the medulla.³

For decades, physiologists have been intrigued with the tenuous balance of oxygen supply and demand in the relatively hypoxic renal medulla. Indeed, the extremes of this equation for the mTAL are unparalleled among mammalian tissues and place this nephron segment at high risk for hypoxic cellular dysfunction and injury.^{4 5 6} Numerous studies in animals have implicated imbalances in oxygen . . . [Full Text of this Article]

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