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Organ Distribution of ^99mTc-and ⁵¹Cr-Labeled Thymocytes

University of Kansas Medical Center, College of Health Sciences and Hospital, Kansas City, Kansas

Correspondence: For reprints contact: Rolf F. Barth, Dept. of Pathology and Oncology, University of Kansas Medical Center, Rainbow Blvd. at 39th St., Kansas City, Kans. 66103.

ABSTRACT

We have employed ^99mTc as a radioisotopic label to study the organ distribution of murine thymocytes. The compartmentalization of ^99mTc-labeled cells that had not been reduced by treatment with stannous chloride was similar to that of ⁵¹Cr-labeled cells and was characterized initially by 48–50% uptake of the injected radioactivity by the lungs. Increased hepatic and splenic and decreased pulmonary localization were noted at 1 hr and these shifts were more pronounced by 4 hr. Technetium-99m-labeled cells reduced by stannous chloride had significantly different patterns of hepatic, pulmonary, and splenic localization and at 4 hr the lungs still retained 24% of the injected radioactivity compared with only 3% in the spleen. Size distribution studies revealed that unlabeled as well as unreduced and reduced ^99mTc-labeled thymocytes were almost identical to one another so that differences in compartmentalization could not be attributed to this factor. Since reduction with stannous chloride did not alter the distribution of ⁵¹Cr-labeled cells, this suggested some type of complex interaction between stannous ions and the labeling species of ^99mTc. The in vivo localization of intravenously administered Na^99mTcO₄ and Na₂CrO₄ was markedly different from the corresponding radiolabeled cells thereby indicating that the distribution patterns that we observed truly represented cell-associated radioactivity. Although it may not necessarily be the proper reference point, the similarity in organ distribution of ^99mTc- and ⁵¹Cr-labeled cells should allow direct comparison of previously reported data employing this radionuclide and that obtained in future studies with ^99mTc.