This study was undertaken to investigate the correlation between gastrointestinal absorption of radioisotopes and uptake by the critical organ during the same period using85Sr, 109Cd, 131I and203Hg as radioisotcpes. When the distribution of85Sr, 109Cd, 131I and203Hg in mice were investigated by means of the whole body autoradiography, these critical organs were determined as follows; 85Sr: bone, 109Cd: liver, 131I: thyroid gland and203Hg: kidney. When the correlation between the injected dose and the uptake dose by the critical organ of85Sr, 109Cd, 131I and203Hg were investigated, uptake dose by the critical organ expressed as cpm per gram of organ was in direct proportion to the injected dose and that expressed as % of the injected dose per gram of organ was held constant in either case. When the coefficient of correlation between gastrointestinal absorption and uptake by the critical organ of85Sr, 109Cd 131I and203Hg were calculated, a positive correlation was revealed in either case. It is concluded from the results obtained that in vivo or in situ method, gastrointestinal absorption of radioisotopes received a support from uptake by the critical organ during the same period.
Biologic distribution of99mTc-labeled fibrinolytic agent, urokinase, and99mTc-labeled mannitol, which was obtained as a side-product in the preparation of99mTc (Sn) -urokinase, have been studied in Ehrlich's tumor-bearing mice to get a promising indicator for the positive delineation of malignant tumor. The preparation of99mTc-labeled radiophar-maceuticals, 99mTc-UK and99mTc-Man, was made by the reduction with stannous chloride and labeling efficiency was examined by Sephadex G-25M gel chromatography and by silica gel plate thin layer chromatography. Labeling yield of99mTc-UK by Sephadex G-25M in 0.9% NaCl eluant was 13% and that of99mTc-Man by TLC in 85% methanol solvent was over 95%. A higher uptake to the implanted solid tumor tissue in mice was found in99mTc-Man than in99mTc-UK, of which the excellent tumor accumulation was expected from the positive delineation of malignant tumor with131I-fibrinogen, 131I-fibrinogen antibody and125I-plasmin. The poor result in99mTc-UK, however, may be attributed to the poor fibrinolytie activity of Ehrlich's tumor. In biologic distribution of99mTc-UK was found high concentration for liver, kidney and stomach. In the other hand, a higher tumor tissue uptake, a fast blood disappearance and a low concentration for different organs were found in biologic distribution of99mTc-Man. Therefore, 99mTc-Man may be assumed as a more preferable99mTc-labeled tumor localizing radiopharmaceuticals, to which it would be needed as absolute biologic characteristics that99mTc-labeled compounds possess a high tumor uptake as well as a fast blood disappearance with a low uptake for different organs. However, the possible delineation with99mTc-labeled fibrinolytic agents, including urokinase and streptokinase, may be promised for malignant tumors in human-subject, which generally have a higher activity in fibrinogenesis than in febrinolysis.
The localization of169Yb, 67Ga and111In in tumor tissues was determined macroauto-radiographically. 169Yb-citrate, 67Ga-citrate and 111In-citrate were injected intravenously to the rats subcutaneously transplanted Yoshida sarcoma and were injected intraperitoneally to the mice subcutaneously transplanted Ehrlich tumor. These animals were sacrificed 3, 24 and 48 hours after injection. These tumor tissues were frozen in n-hexane (-70°C) cooled with dry ice-acetone. After this, these frozen tumor tissues were cut into serial thin sections (10μm) in the cryostat (-20°C) . One of the slice of these sections was then placed on X-ray film and this film was developed after exposure of several days. On the other hand, next slice of these sections were then stained using the hematoxylin and eosin. From the observations of these autoradiogram and H·E stained slice, the following results were obtained. Concentration of169Yb, 67Ga and111In was predominant in viable tumor tissue rather than in necrotic tumor tissue, regardless of time after the administration. 67Ga and111In were distributed uniformly in viable tumor tissue, but deposition of169Yb was observed more avidly in viabl tumor tissue neighboring to necrotic tumor.
We have been studies time sequent stability each on standard human·C-peptide, human·C-peptide antiserum, 125I-tyrosyl human·C-peptide and the assay kit (all reagent) which is necessary in human proinsulin·C-peptide radioimmunoassay (RIA) . Also we measured using this assay system, human proinsulin·C-peptide in blood after oral administration of glucose to normal subject. Standard human·C-peptide and human·C-peptide antiserum were very stable on storage at 4°C, 125I-tyrosyl human·C·peptide was unstable as compared with the former two, The stability of the assay kit was influenced by the stability of125I-tyrosyl human·C-peptide, and was stable at 4°C for ten weeks after preparation. Three lots of the assay kit prepared at different period showed almost same stability. We think this assay system using the assay kit is satisfactory in respect of stability. The measured values of human proinsulin·C-peptide in blood, using this assay system, showed insulin secretory reaction after oral administration of glucose.
A prototype81mKr-generator consisting of an ion exchange column and some attachments for handling was prepared on trial. Parent nuclide81Rb obtained by the reaction of82Kr (p, 2n) 81Rb was absorbed on the resin, and radionuclidic purity, sterility and apyrogenicity of the generator eluate were examined. Analysis of γ-ray spectrum obtained with a Ge (Li) detector and a multichannel pulse height analyzer revealed that the nuclidic purity of the81mKr in the eluate was 99.997-99.999% with 0.001-0.003% of79Kr at the start of the elution. Sterility and apyrogenicity of the eluate were proved by J.P, sterility test and limulus test respectively. All results obtained show that the81mKr-generator is very suitable for medical application.