Pathophysiology of the Medullary Circulation. In: Robinson RR, Dennis VW, Ferris TF, Glassock RJ, Kokko JP, Tisher CC, editors. Nephrology. New York: Springer; 1984. pp. 107-19. [DOI: 10.1007/978-1-4612-5284-9_11]

[Kidney medullary hypoxia: a key to understanding acute renal failure?]

The ability to produce a concentrated urine is imposed by a uniquely low ambient oxygen pressure in the renal medulla due to shunt diffusion within the vascular bundles. As the thick ascending limb of Henle's loop (TAL-segment) is able to glycolyse anaerobically, a phase of oxygen deficiency may be bridgespanned. It allows an exceptionally high oxygen extraction of 80% in this area. If oxygen capacity is reduced systematically, which can be effected in the isolated kidney model by using cell free perfusate, a typical pattern of lesions occur in TAL-segments. Segments near vascular bundles remain intact, as they take advantage from a radial oxygen diffusion originating from vascular bundles. The extent of lesions is increasing directed to the inner medulla due to the reduction of oxygen pressure, whereas lesions are not present in the inner medulla itself. Cells of TAL-segments are swelling during oxygen deficiency, when transport work surpasses the available energy necessary due to the luminal fluid inflow. Lesions could be prevented, when oxygen capacity was enhanced by adding erythrocytes or when transport was blocked by furosemide. Swollen cells in TAL-segments however are able to aggravate medullary hypoxia by an outflow block in vivo. Secondly, it can be demonstrated, that oxygen shunt diffusion is not only present in renal medulla but also within renal cortex especially as a preglomerular diffusion shunt for blood gases. Thus PCO2 has been measured to be 65 mmHg in the outermost cortical zone and thereby some 20 mmHg higher than renal venous blood.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cold ischemia and reperfusion on trapping of erythrocytes in the rat kidney

After reperfusion of kidneys subjected to a period of warm ischemia, the medulla displays a vascular congestion of erythrocytes, especially in the inner stripe of the outer zone, a phenomenon referred to as "trapping." This trapping causes reflow alterations, thus contributing to postperfusion medullary ischemia. The purpose of the present investigation was to study whether trapping also occurs after reperfusion of kidneys following varying periods of cold ischemia and to determine if there is any correlation between the degree of cold ischemic injury and the extent of erythrocyte trapping. Rat kidneys stored at +4 degrees C for 0-30 h were transplanted into recipient animals pretreated with a 51Cr-labelled erythrocyte suspension. Twenty minutes after reperfusion, the grafts were removed and microdissected into cortex, outer and inner stripes of the outer medullary zone, and inner zone, respectively. The radioactivity of these specimens was measured, and the erythrocyte content for each specimen was calculated. The results show a maximal trapping for cold ischemia time (CIT) of about 12-15 h. A linear correlation between the amount of trapping and CIT could be found in all parts of the kidney (except for the cortex) for CIT 0-15 h. The best correlation was found in the part where the trapping was most prominent, i.e., in the inner stripe. After CIT of 15 h or more, no correlation could be found. It is suggested, as described in models of warm ischemia, that the obstructions of the capillaries by trapped erythrocytes following reperfusion is of pathophysiological significance for the development of post-transplant acute renal failure.(ABSTRACT TRUNCATED AT 250 WORDS)