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Compartmental Redistribution of ^99mTc-Pertechnetate in the Presence of Perchlorate Ion and its Relation to Plasma Protein Binding

Wadsworth Hospital, Veterans Administration Center, Los Angeles, California
UCLA School of Medicine, Los Angeles, California

Correspondence: For reprints contact: William H. Oldendorf, Veterans Administration Center, Wilshire and Sawtelle Blvds., Los Angeles, Calif. 90073.

ABSTRACT

It was shown in rabbits that the addition of 3 mg/kg of perchlorate (ClO₄^–) ion results in a major tissue redistribution of pertechnetate (TcO₄). This probably results from (1) release of TcO₄ from plasma protein binding sites with resulting redistribution to tissue extracellular spaces and (2) a shift of a portion of the TcO₄^– intracellularly. The injection of this dose of ClO₄^– results in tissue levels relative to blood plasma about 1.38 times greater than without ClO₄^–.

In the presence of ClO₄,^–, TcO₄^– moves from plasma into red cells. The ClO₄^– dose dependence of this plasma-to-red cell shift was studied in vivo. The ratio of plasma-to-red cell concentration of TcO₄^– shifts from 3.98 ± 0.3 1 without ClO₄^– to 1.98 ± 0.32 with 3 mg/kg of ClO₄^–. This intracellular shift was demonstrated in vitro at a single high concentration of ClO₄^– producing a ratio of 1.25.

The effect of ClO₄^– on plasma-to-red cell distribution is complete within 1 min of i.v. injection in the rabbit.

Chloride does not redistribute between red cellsand plasma as does TcO₄^– in response to ClO₄^–.

Preliminary dialysis studies indicate about 80% of plasma TcO₄^– is protein bound in rabbit and man. This drops to about 40% in the presence of ClO₄^– concentrations used in this study in the rabbit but changes very little in man.

The tissue compartmental redistribution in the presence of ClO₄^– described here is not expected to produce visible changes in clinical scan appearance except in those organs where active uptake is present.

Possible mechanisms responsible for this redistribution are discussed.