Bone Uptake of ^99mTc-Phosphate via Labeled Plasma Protein^[*]

The transfer of albumin into the extravascular space of bone and other tissues was evaluated in the non-adult rat and was found to be less rapid in bone than in the liver and kidneys but more rapid than in muscle. Protein binding of ^99mTc increased continuously with time after injection of ^99mTc-EHDP and -PPi. One hour after administration, about 20% of the plasma activity of ^99mTc-EHDP and 90% of ^99mTc-PPi was bound to proteins. Thus the possibility exists that the fetation of ^99mTc through protein binding in the extravascular space of bone contributes significantly to the regular bone uptake of ^99mTc-phosphates, in the event that relatively unstable compounds such as ^99mTc-PPi are used.

Die Abwanderung von Albumin in den Extravasalraum des Knochens und anderer Gewebe wurde in der jungen Ratte bestimmt. Im Knochen erfolgte sie weniger rasch als in der Leber und in den Nieren, aber schneller als im Muskel. Die Proteinbindung von ^99mTc nach Injection von ^99mTc-EHDP und -PPi nahm konstant zu. Nach einer Stunde war bei ^99mTc- EHDP 20%, bei "^99mTc-PPi dagegen 90% der Plasmaaktivität an Proteine gebunden. Daher ist die Möglichkeit gegeben, daß die Fixation von ^99mTc durch Proteinbindung im Extravasalraum des Knochens zur normalen Knochenanreicherung der ^99mTc-Phosphate beiträgt, sofern wenig stabile Verbindungen wie ^99mTc-PPi eingesetzt werden.

^* Dedicated to Prof. Dr. K. E. Scheer on the occasion of his 60^th birthday.

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