Serial gross autoradiographs of rabbit kidneys revealed marked differences in the intrarenal distribution of various radioactive diagnostic agents following intravascular injection. From about 10 to 50 see after injection, the radioactivity concentrated predominantly in the contex. For121I Hippuran,122Xe and simple ions such as25F and131Cs, the concentration increased in the medulla as the cortex cleared. Some substances, including205Hg chlormerodrin and labeled low-molecular-weight proteins were retained by the renal tubular cells of the cortex and did not reach a high concentration in the medulla. A narrow band of high concentration of labeled chlormerodria was observed at the corticomedullary junction in rodents, but not in man or the rhesus monkey.99mTc, as pertechnetate or Tc-DTPA complex readily diffused through the kidney into the urine: as a Tc-Fe ascorbate complex, however, a significant fraction was retained in the renal cortex.121I macroaggregated albumin and141Ce-labeled ceramic microspheres injected into the aorta localized exclusively in the renal cortex. Selective vascular obstruction of the peripheral cortex was obtained by a prior injection of numerous nonradioactive microspheres.
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