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Localization of Polypeptide Caseidin in the Renal Cortex: A New Radioisotope Carrier for Renal Studies

Donner Laboratory, University of California, Berkeley, California

Correspondence: For reprints contact: H. S. Winchell, Donner Laboratory, University of California, Berkeley, Calif. 94720.

ABSTRACT

The polypeptide caseidin labeled with ^99mTc using the Fe(III) plus ascorbate method, the Fe(II) method, the Sn(II) method, or labeled with ⁵¹Cr localizes in the renal cortex of mice, rats, and dogs. Fifteen minutes after i.v. administration of ^99mTc-caseidin to mice, rats, and dogs approximately one third of the administered activity is in the kidneys and the ratio of activities in the kidney to that in the liver is 4.8:1.

Retention of ⁵¹Cr activity in the kidney is prolonged following administration of ⁵¹Cr-caseidin since in two dogs sacrificed 51 and 53 days after administration of ⁵¹Cr-caseidin radioactivity in the kidney was 50 and 40% of the activity remaining in the body, respectively. The pattern of retention of activity in mice which were germ free before administration of ⁵¹Cr-caseidin was different from that in mice which were not germ free.

The rapid accumulation of a large fraction of activity in the renal cortex following administration of ^99mTc- or ⁵¹Cr-labeled caseidin suggests the usefulness of caseidin as a radionuclide carrier for renal studies.

The concentration and possible prolonged retention of labeled caseidin and other polypeptides in the renal cortex suggests a role of the kidney in the body's response to foreign protein. The possible nature of this role is discussed.

The initial intravascular distribution, subsequent rapid plasma clearance, and the molecular size of labeled caseidin indicate its possible suitability for imaging brain lesions.

FOOTNOTES

^* Director of Polymer Dept., Weizmann Institute, Rehoveth, Israel, and Visiting Professor, Division of Medical Physics, University of California, Berkeley, Calif.