Concentration gradient of oxalate from cortex to papilla in rat kidney.
BACKGROUND
The kidney eliminates the major fraction of plasma oxalate. It is well known that oxalate is freely filtered by glomeruli and secreted by the proximal tubules. However, the renal handling of oxalate in distal nephrons, which is considered as playing an important role in stone formation, remains obscure.


METHODS
At 15-180 min after intravenous injection of 14C-oxalate to rats, the intrarenal localization of radioactivity was quantitatively measured by the radioluminographic method using a bioimaging analyzer. Tissue radioactivity was compared with plasma, and urinary radioactivities were measured by a liquid scintillation counter. The control study was conducted with 14C-inulin.


RESULTS
The radioactivity of 14C-oxalate in the papilla was 10 times greater than in the cortex and eight times greater than in the medulla 180 min after injection when almost no radioactivity was present in the urine. In contrast, the radioactivity of 14C-inulin was nine times less in the papilla than in the cortex at the same time.


CONCLUSIONS
Oxalate remains in the renal papilla for an extended period. This accumulation of oxalate may be attributed to calcium oxalate crystal fixation along the deep nephron which is considered to be the first step of stone formation.
Nakatani
Tatsuya
T
Department of Urology, Osaka City University Medical School, Osaka, Japan. nakatani@msic.med.osaka-cu.ac.jp
Ishii
Keiichi
K
Sugimoto
Toshikado
T
Kamikawa
Sadanori
S
Yamamoto
Keisuke
K
Yoneda
Yukio
Y
Kanazawa
Toshinao
T
Kishimoto
Taketoshi
T
D000818:Animals; D001345:Autoradiography; D002129:Calcium Oxalate / Q000493:pharmacokinetics / Q000494:pharmacology*; D004195:Disease Models, Animal; D007275:Injections, Intravenous; D007669:Kidney Calculi / Q000378:metabolism; D007672:Kidney Cortex / Q000000981:diagnostic imaging*; D007679:Kidney Medulla / Q000000981:diagnostic imaging*; D008297:Male; D011868:Radioisotopes; D011877:Radionuclide Imaging; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D012680:Sensitivity and Specificity; D016482:Urinalysis
D011868:Radioisotopes; D002129:Calcium Oxalate