Studies on 67Ga uptake by mouse granuloma tissues

The Effect of Blood Decrease on 67Ga Uptake by the Liver in Partially Hepatectomized Rats

As (67)Ga is injected into the blood, (67)Ga is immediately bound to transferrin (Tf) and transported to various tissues and the Tf-(67)Ga complex binds to Tf receptor on various tissues. In partial hepatectomy (PH) a part of blood in circulation is lost together with removed liver tissues, consequently the amounts of blood cells and Tf in circulation decrease. In order to investigate the effect of those decreases on (67)Ga uptake by the liver, we compared the uptake in partially hepatectomized rats with that in venesectioned rats in which only a part of blood in circulation decreased. A two-thirds PH was performed. Two milliliters of blood was venesectioned. Each treated rat was intraveneously injected with (67)Ga. The changes of erythrocyte and reticulocyte contents after PH did not differ from those after venesection (VS) at all. But (67)Ga uptake by reticulocytes significantly increased after VS but did not after PH. On the other hand, (67)Ga uptake by the liver significantly increased after PH but did not after VS. These differences must be related to the different expression of Tf receptors on the liver after PH and VS.

The Entering of Indium-111 and Iron-59 into the Hepatocytes from Partially Hepatectomized Rats Differ from That of Gallium-67

We recently suggested that the transferrin (Tf)-gallium-67 (67Ga) complex dissociated on the surface of the hepatocytes after partial hepatectomy and free 67Ga bound to heparan sulfate in the extracellular matrix. In the present study, we investigated whether the entering of indium-111 (111In) and iron-59 (59Fe) with high affinity to transferrin differed from the entering of 67Ga by the hepatocytes after partial hepatectomy. 111In was almost taken by the plasma and little taken by the red blood cell. On the other hand, the uptake of 59Fe by the red blood cell was higher than plasma. The uptake of 59Fe by the bone marrow was significantly higher than that of 111In. The uptake of 111In and 59Fe by the liver tissue was reached a maximum 2 d after partial hepatectomy but the uptake ratio of 111In was lower than that of 59Fe. We suspected that the uptake of 59Fe by the liver tissue was the highest because of the high binding affinity of Tf-59Fe to Tf-receptor. The entering of 111In and 59Fe into the hepatocytes was also reached a maximum 2 d after partial hepatectomy but the ratio of 59Fe was slightly lower than that of 111In. These results suggested that the binding affinity to Tf could have played a crucial role in the differences of the entering of 111In, 59Fe and 67Ga into the hepatocytes of partially hepatectomized rats.

Application of 67Ga for the estimation of reticulocyte production

In order to estimate the production of reticulocytes, which have a larger number of transferrin receptors than erythrocytes, we used 67Ga which is exclusively bound to transferrin in the blood. The pattern of uptake of 67Ga by reticulocytes was quite similar to the time course of transglutaminase activity which might be involved in receptor-mediated endocytosis. The preinjection of Fe3+ decreased the uptake of 67Ga by reticulocytes. These results suggested that 67Ga in a transferrin-bound form was taken up by reticulocytes via receptor-mediated endocytosis. It was showed that the application of 67Ga is very easy and useful for the estimation of reticulocyte production.