Modeling principles of protective thyroid blocking.

PURPOSE: In the case of a nuclear incident, the release of radioiodine must be expected. Radioiodine accumulates in the thyroid and by irradiation enhances the risk of cancer. Large doses of stable (non-radioactive) iodine may inhibit radioiodine accumulation and protect the thyroid ('thyroid blocking'). Protection is based on a competition at the active carrier site in the cellular membrane and an additional temporary inhibition of the organification of iodide (Wolff-Chaikoff effect). Alternatively, other agents like e.g. perchlorate that compete with iodide for the uptake into the thyrocytes may also confer thyroidal protection against radioiodine exposure.Biokinetic models for radioiodine mostly describe exchanges between compartments by first order kinetics. This leads to correct predictions only for low (radio)iodide concentrations. These models are not suited to describe the kinetics of iodine if administered at the dosages recommended for thyroid blocking and moreover does not permit to simulate either the protective competition mechanism at the membrane or the Wolff-Chaikoff effect. Models adapted for this purpose must be used. Such models may use a mathematical relation between the serum iodide concentration and a relative uptake suppression or a dependent rate constant determining total thyroidal radioiodine accumulation. Alternatively, the thyroidal uptake rate constant may be modeled as a function of the total iodine content of the gland relative to a saturation amount. Newer models integrate a carrier-mechanism described by Michalis-Menten kinetics in the membrane and in analogy to enzyme kinetics apply the rate law for monomolecular irreversible enzyme reactions with competing substrates to model the competition mechanism. An additional total iodide uptake block, independent on competition but limited in time, is used to simulate the Wolff-Chaikoff effect. CONCLUSION: The selection of the best model depends on the issue to be studied. Most models cannot quantify the relative contributions of the competition mechanism at the membrane and the Wolff-Chaikoff effect. This makes it impossible or exceedingly difficult to simulate prolonged radioiodine exposure and the effect of repetitive administrations of stable iodine. The newer thyroid blocking models with a separate modeling of competition and Wolff-Chaikoff effect allow better quantitative mechanistic insights and offer the possibility to simulate complex radioiodine exposure scenarios and various protective dosage schemes of stable iodine relatively easily. Moreover, they permit to study the protective effects of other competitors at the membrane carrier site, like e.g. perchlorate, and to draw conclusions on their protective efficacy in comparison to stable iodine.

A comparison of thyroidal protection by stable iodine or perchlorate in the case of acute or prolonged radioiodine exposure.

In the case of a nuclear power plant accident, repetitive/prolonged radioiodine release may occur. Radioiodine accumulates in the thyroid and by irradiation enhances the risk of cancer. Large doses of non-radioactive iodine may protect the thyroid by inhibiting radioiodine uptake into the gland (iodine blockade). Protection is based on a competition at the active carrier site in the cellular membrane and the Wolff-Chaikoff effect, the latter being, however, only transient (24-48 h). Perchlorate may alternatively provide protection by a carrier competition mechanism only. Perchlorate has, however, a stronger affinity to the carrier than iodide. Based on an established biokinetic-dosimetric model developed to study iodine blockade, and after its extension to describe perchlorate pharmacokinetics and the inhibition of iodine transport through the carrier, we computed the protective efficacies that can be achieved by stable iodine or perchlorate in the case of an acute or prolonged radioiodine exposure. In the case of acute radioiodine exposure, perchlorate is less potent than stable iodine considering its ED50. A dose of 100 mg stable iodine has roughly the same protective efficacy as 1000 mg perchlorate. For prolonged exposures, single doses of protective agents, whether stable iodine or perchlorate, offer substantially lower protection than after acute radioiodine exposure, and thus repetitive administrations seem necessary. In case of prolonged exposure, the higher affinity of perchlorate for the carrier in combination with the fading Wolff-Chaikoff effect of iodine confers perchlorate a higher protective efficacy compared to stable iodine. Taking into account the frequency and seriousness of adverse effects, iodine and perchlorate at equieffective dosages seem to be alternatives in case of short-term acute radioiodine exposure, whereas preference should be given to perchlorate in view of its higher protective efficacy in the case of longer lasting radioiodine exposures.

Change of iodine load and thyroid homeostasis induced by ammonium perchlorate in rats.

Ammonium perchlorate (AP), mainly used as solid propellants, was reported to interfere with homeostasis via competitive inhibition of iodide uptake. However, detailed mechanisms remain to be elucidated. In this study, AP was administered at 0, 130, 260 and 520 mg/kg every day to 24 male SD rats for 13 weeks. The concentrations of iodine in urine, serum thyroid hormones levels, total iodine, relative iodine and total protein, and malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT) activity in thyroid tissues were measured, respectively. Our results showed that high-dose perchlorate induced a significant increase in urinary iodine and serum thyroid stimulating hormone (TSH), with a decrease of total iodine and relative iodine content. Meanwhile, free thyroxine (FT4) was decreased and CAT activity was remarkably increased. Particularly, the CAT activity was increased in a dose-dependent manner. These results suggested that CAT might be enhanced to promote the synthesis of iodine, resulting in elevated urinary iodine level. Furthermore, these findings suggested that iodine in the urine and CAT activity in the thyroid might be used as biomarkers for exposure to AP, associated with thyroid hormone indicators such as TSH, FT4.

Iodine uptake and prostate cancer in the TRAMP mouse model.

Iodine supplementation exerts antitumor effects in several types of cancer. Iodide (I⁻) and iodine (I2) reduce cell proliferation and induce apoptosis in human prostate cancer cells (LNCaP and DU-145). Both chemical species decrease tumor growth in athymic mice xenografted with DU-145 cells. The aim of this study was to analyze the uptake and effects of iodine in a preclinical model of prostate cancer (transgenic adenocarcinoma of the mouse prostate [TRAMP] mice/SV40-TAG antigens), which develops cancer by 12 wks of age. ¹²5I⁻ and ¹²5I2 uptake was analyzed in prostates from wild-type and TRAMP mice of 12 and 24 wks in the presence of perchlorate (inhibitor of the Na⁺/I⁻ symporter [NIS]). NIS expression was quantified by quantitative polymerase chain reaction (qPCR). Mice (6 wks old) were supplemented with 0.125 mg I⁻ plus 0.062 mg I2/mouse/day for 12 or 24 wks. The weight of the genitourinary tract (GUT), the number of acini with lesions, cell proliferation (levels of proliferating cell nuclear antigen [PCNA] by immunohistochemistry), p53 and p21 expression (by qPCR) and apoptosis (relative amount of nucleosomes by enzyme-linked immunosorbent assay) were evaluated. In both age-groups, normal and tumoral prostates take up both forms of iodine, but only I⁻ uptake was blocked by perchlorate. Iodine supplementation prevented the overexpression of NIS in the TRAMP mice, but had no effect on the GUT weight, cell phenotype, proliferation or apoptosis. In TRAMP mice, iodine increased p53 expression but had no effect on p21 (a p53-dependent gene). Our data corroborate NIS involvement in I⁻ uptake and support the notion that another transporter mediates I2 uptake. Iodine did not prevent cancer progression. This result could be explained by a strong inactivation of the p53 pathway by TAG antigens.

[Dracorhodin perchlorate inhibit high glucose induce serum and glucocorticoid induced protein kinase 1 and fibronectin expression in human mesangial cells].

OBJECTIVE: To investigate the effect of dracorhodin perchlorate (DP) on inhibiting high glucose-induced serum and glucocorticoid induced protein kinase 1 (SGK1) and fibronectin (FN) expression in human mesangial cells (HMC), and its mechanism of prevention and treatment on renal fibrosis in diabetic nephropathy (DN) . METHOD: The HMC were divided into normal glucose group (NG group, 5.5 mmol x L(-1) D-glucose), normal glucose +low DP group (NG + LDP group, 5.5 mmol x L(-1) D-glucose +7.5 micromol x L(-1) DP), normal glucose +high DP group (NG + HDP group, 5.5 mmol x L(-1) D-glucose + 15 micromol x L(-1) DP), high glucose group (HG group,25 mmol x L(-1) D-glucose), high glucose +low DP group (HG + LDP group, 25 mmol x L(-1) D-glucose + 7.5 micromol x L(-1) DP)and high glucose +high DP group (HG +HDP group, 25 mmol x L(-1) D-glucose + 15 micromol x L(-1) DP). Each group was examined at 24 hours. The levels of SGK1 and FN mRNA was detected by real-time fluorescence quantitative PCR,and the expression of SGK1 and FN protein was detected by Western blot or indirect immunofluorescence. RESULT: A basal level of SGK1 and FN in HMC were detected in NG group, and the level of SGK1 and FN mRNA and protein were not evidently different compared to that of NG group adding 7.5 micromol x L(-1) DP for 24 hours. On the other hand, the levels of SGK1 and FN mRNA and protein were obviously decreased by adding 15 micromol x L(-1) DP for 24 hours. Compared to NG group, the levels of SGK1 and FN mRNA and protein were increased in HG group after stimulating for 24 hours (P < 0.01). Compared to HG group, the level of SGK1 and FN mRNA and protein were evidently reduced in HG + LDP and HG + HDP groups by adding 7.5 micromol x L(-1) DP and 15 micromol x L(-1) DP for 24 hours (P < 0.01). CONCLUSION: Dracorhodin perchlorate can inhibit high glucose-induced serum and glucocorticoid induced protein kinase 1 (SGK1) and fibronectin(FN) expression in human mesangial cells, and this may be part of the mechanism of preventing and treating renal fibrosis of DN.

Cell-based imaging of sodium iodide symporter activity with the yellow fluorescent protein variant YFP-H148Q/I152L.

The sodium iodide symporter (NIS) mediates iodide (I(-)) transport in the thyroid gland and other tissues and is of increasing importance as a therapeutic target and nuclear imaging reporter. NIS activity in vitro is currently measured with radiotracers and electrophysiological techniques. We report on the development of a novel live cell imaging assay of NIS activity using the I(-)-sensitive and genetically encodable yellow fluorescent protein (YFP) variant YFP-H148Q/I152L. In FRTL-5 thyrocytes stably expressing YFP-H148Q/I152L, I(-) induced a rapid and reversible decrease in cellular fluorescence characterized by 1) high affinity for extracellular I(-) (35 muM), 2) inhibition by the NIS inhibitor perchlorate, 3) extracellular Na(+) dependence, and 4) TSH dependence, suggesting that fluorescence changes are due to I(-) influx via NIS. Individual cells within a population of FRTL-5 cells exhibited a 3.5-fold variation in the rate of NIS-mediated I(-) influx, illustrating the utility of YFP-H148Q/I152L to detect cell-to-cell difference in NIS activity. I(-) also caused a perchlorate-sensitive decrease in YFP-H148Q/I152L fluorescence in COS-7 cells expressing NIS but not in cells lacking NIS. These results demonstrate that YFP-H148Q/I152L is a sensitive biosensor of NIS-mediated I(-) uptake in thyroid cells and in nonthyroidal cells following gene transfer and suggest that fluorescence detection of cellular I(-) may be a useful tool by which to study the pathophysiology and pharmacology of NIS.

Visualization of endogenous p53-mediated transcription in vivo using sodium iodide symporter.

PURPOSE: To develop a gamma camera imaging method for the determination of endogenous gene expression, we evaluated the expression of endogenous p53 gene using human sodium iodide symporter (hNIS) gene as reporter. EXPERIMENTAL DESIGN: We constructed cis-p53RE-hNIS reporter vector placed under control of an artificial enhancer (p53RE). Moreover, we transfected it into human hepatoma cell line SK-Hep1 by liposome. Geneticin was used for the selection of stable transfectant (SK-Hep1p53NIS). To evaluate the function of hNIS, the inhibition study was examined with 1 mmol/L potassium perchlorate. After treatment of Adriamycin with serial dose for 24 hours, we measured the uptake of 125I and did Western blot analysis to evaluate expression of p53 protein. Tumor xenografts were produced in nude mice by s.c. injection of SK-Hep1p53NIS cells. After 7 days, scintigraphic images of nude mice before and after Adriamycin treatment were obtained using [99mTc]-pertechnetate. RESULTS: In the SK-Hep1p53NIS cells, Adriamycin-treated cells accumulated up to three times higher than did nontreated cells. Potassium perchlorate inhibited completely the uptake of 125I. As Adriamycin dose increased, radioiodide uptake was significantly correlated with activated p53 as well as total p53 protein level. When Adriamycin (2 mg/kg) was treated in the same mice, a significantly higher uptake of [99mTc]-pertechnetate was observed in SK-Hep1p53NIS xenografts compared with nontreated xenografts (P < 0.05, unpaired t test). CONCLUSIONS: These results suggest that p53 expression level can be monitored by NIS gene expression using cis-p53RE-hNIS system in vitro and in vivo.

Adenovirus biodistribution and noninvasive imaging of gene expression in vivo by positron emission tomography using human sodium/iodide symporter as reporter gene.

Amongst the various methods that can be developed for noninvasive monitoring of gene expression in vivo, the use of positron emission tomography (PET) appears to be the most promising both for preclinical and clinical studies. Various genes have been described as potential PET reporters, but there is a need to develop new approaches that exploit transgenes with both therapeutic and imaging potential. The Na/I symporter (NIS) gene is expressed mainly in the thyroid and is responsible for iodide accumulation in this organ. The NIS gene has been used in gene therapy experimentation. Ectopic expression of this gene in various type of malignant cells has led to radiosensitization and in some cases tumor regression in xenograft models in nude mice, highlighting the therapeutic potential of this approach. In the present study, we demonstrate the potential of the human NIS gene (hNIS) as a reporter gene. Expression of hNIS, after plasmid transfection or adenoviral gene delivery, can be monitored in vitro on incubation with (125)I. Iodide uptake in the transduced cells can be directly correlated with the levels of gene expression in vitro. Ectopic expression of the NIS gene in vivo can be monitored in biodistribution studies on intravenous injection of (125)I. Adenovirus delivery induces gene expression essentially in the liver, adrenal glands, lungs, pancreas, and spleen. Expression of hNIS in tumor xenograft models can also be detected when the virus is injected intratumorally. Finally, hNIS expression was monitored by PET after intravenous injection of (124)I, demonstrating the potential of this approach for noninvasive imaging.

Functional characterization of the recombinant type 3 Ca2+ release channel (ryanodine receptor) expressed in HEK293 cells.

To investigate the channel properties of the mammalian type 3 ryanodine receptor (RyR3), we have cloned the RyR3 cDNA from rabbit uterus by reverse transcriptase-polymerase chain reaction and expressed the cDNA in HEK293 cells. Immunoblotting studies showed that the cloned RyR3 was indistinguishable from the native mammalian RyR3 in molecular size and immunoreactivity. Ca2+ release measurements using the fluorescence Ca2+ indicator fluo 3 revealed that the cloned RyR3 functioned as a caffeine- and ryanodine-sensitive Ca2+ release channel in HEK293 cells. Functional properties of the cloned RyR3 were further characterized by using single channel recordings in lipid bilayers. The cloned RyR3 channel exhibited a K+ conductance of 777 picosiemens in 250 mM KCl and a Ca2+ conductance of 137 picosiemens in 250 mM CaCl2 and displayed a pCa2+/pK+ ratio of 6.3 and an open time constant of about 1.16 ms. The response of the cloned RyR3 to cytoplasmic Ca2+ concentrations was biphasic. The channel was activated by Ca2+ at about 100 nM and inactivated at about 10 mM. Ca2+ alone was able to activate the cloned RyR3 fully. Calmodulin activated the cloned RyR3 at low Ca2+ concentrations but inhibited the channel at high Ca2+ concentrations. The cloned RyR3 was activated by ATP, caffeine, and perchlorate, inhibited by Mg2+ and ruthenium red, and modified by ryanodine. Cyclic ADP-ribose did not seem to affect single channel activity of the cloned RyR3. The most prominent differences of the cloned RyR3 from the rabbit skeletal muscle ryanodine receptor were in the gating kinetics, extent of maximal activation by Ca2+, and sensitivity to Ca2+ inactivation. Results of the present study provide initial insights into the single channel properties of the mammalian RyR3.

Selenium deficiency and thyroid fibrosis. A key role for macrophages and transforming growth factor beta (TGF-beta).

Free radical damage and fibrosis caused by selenium deficiency are thought to be involved in the pathogenesis of myxoedematous cretinism. So far, no pathway explains the link between selenium deficiency and tissue fibrosis. Pharmacological doses of iodine induce necrosis in iodine-deficient thyroids. Necrosis is much increased if the glands are also selenium-deficient, which then evolve to fibrosis. This rat model was reproduced to explore the role of selenium deficiency in defective tissue repair. At first, proliferation indexes of epithelial cells and fibroblasts were comparable between selenium-deficient and control groups. Then, in selenium-deficient thyroids the inflammatory reaction was more marked being mainly composed of macrophages. The proliferation index of the epithelial cells decreased, while that of the fibroblasts increased. These thyroids evolved to fibrosis. TGF-beta immunostaining was prominent in the macrophages of selenium-deficient rats. Anti TGF-beta antibodies restored the proliferation indexes, and blocked the evolution to fibrosis. In selenium deficiency, an active fibrotic process occurs in the thyroid, in which the inflammatory reaction and an excess of TGF-beta play a key role.

The o-diphenol oxidase activity of arthropod hemocyanin.

Arthropod hemocyanin (isolated from the crab Carcinus maenas and the lobster Homarus americanus) is usually referred to as an oxygen transport-storage protein. The protein, however, also catalyses with low efficiency the oxidation of o-diphenol to quinone, similarly to tyrosinase (monophenol, o-diphenol:oxygen oxidoreductase). The enzymatic parameters of hemocyanin are affected by the aggregation state of the protein; namely V(max) exhibited by a dissociated subunit is one order of magnitude greater than that of aggregated species. The reaction velocity is increased by the presence of perchlorate, an anion of the Hofmeister series. The results are also discussed on the basis of active site accessibility in comparison with tyrosinase.

Conformational changes upon dissociation of a globular protein from pea: a Fourier transform infrared spectroscopy study.

Fourier transform infrared spectroscopy shows that the secondary structure of legumin, a globular protein from pea seeds, is composed of 41% beta-sheets and 16% alpha-helices and furthermore reveals the presence of beta-turns. The conformation prediction from the analysis of the amino-acid sequence of legumin using hydrophobic cluster analysis reveals that the C-terminal part of the alpha-polypeptide is devoid of defined secondary structures, whereas the beta-polypeptide is highly ordered. Comparison with analogous 11S globulins from other plant families indicates that ordered domains are highly preserved, phenomenon that may be associated with the similarity of the quaternary structure of these proteins. The results also reveal the presence of a large hypervariable region, located at the surface of the protein, that could be at the origin of the different functional properties of the 11S type globulins. The step-by-step destruction of the quaternary oligomeric structure of the native protein is accompanied by conformational changes that depend on the dissociation conditions. Whereas acylation leads to a decrease of the alpha-helix content by 10% at the expense of the beta-sheet content, addition of sodium perchlorate results in the conversion of 10% of the protein secondary structure from beta-sheet to unordered. These observations provide further evidence of the existence of different monomeric states that differ from their secondary structure and, therefore, exhibit different surface-active properties.

Uptake and metabolism of iodine is crucial for the development of thyroiditis in obese strain chickens.

To assess the importance of the role of thyroidal iodine in the pathogenesis of thyroiditis in the obese strain (OS) chicken, a model of spontaneous and severe disease, we studied the effect of antithyroid drugs that reduce thyroidal iodine or prevent its metabolism. Reduction of thyroidal iodine was achieved with KClO4, an inhibitor of iodine transport and mononitrotyrosine (MNT), a drug that promotes loss of thyroidal iodine as iodotyrosines. A regimen consisting of KClO4 and MNT administration beginning in ovo and continuing after hatching reduced thyroidal infiltration to 2% of control values and decreased thyroglobulin antibody (TgAb) production for as long as 9 wk. Untreated birds had severe disease by 5 wk of age. The suppression of disease was independent of TSH, not mediated by generalized immunosuppression and reversed by excess dietary iodine. Two drugs that inhibit the metabolism of iodine, propylthiouracil (PTU) and aminotriazole, reduced thyroidal infiltration and TgAb levels, although to a lesser extent. When splenocytes from OS chickens with thyroiditis were transferred to Cornell strain (CS) chickens, a related strain that develops late onset mild disease, only the recipients that were iodine supplemented developed thyroiditis. In conclusion, autoimmune thyroiditis in an animal model can be prevented by reducing thyroidal iodine or its metabolism and optimal effects require intervention at the embryonic stage.

An investigation of the dissociation and denaturation of legumin by salts using laser light scattering and circular dichroism spectroscopy.

The dissociation of legumin, a 12 S seed storage globulin from Pisum sativum, has been studied by laser light scattering and circular dichroism spectroscopy. Salts from the Hofmeister series, in particular sodium perchlorate, were used as dissociating agents. The Mr 360,000 hexameric protein was found to dissociate first to trimers and further to monomers and the number of amino acids involved in the trimer-trimer interaction estimated to be 23(+/-4). Native legumin appears to be more strongly bound together than some analogous seed storage globulins from other plant species such as Arachis hypogaea or Sesamum indicum and the dissociation process was accompanied by some changes in conformation.

Effects of a selenium deficient diet on thyroid function of normal and perchlorate treated rats.

Pregnant rats were submitted to a selenium-deficient diet immediately after mating; it was continued for 4 weeks after delivery. The pups were sacrificed at 3 and 4 weeks of age. Perchlorate, an antithyroid agent inhibiting iodide trapping in the thyroid, was administered via the drinking water to half of the rats. Rats submitted to a normal laboratory diet and to the experimental diet supplemented with selenium were used as controls. The effects of selenium deficiency were an increase in the number of growth abnormalities, growth retardation, and decreased seleno-dependent glutathione peroxidase (GSH-Px) activity in plasma and in various organs. These effects were relieved by selenium supplementation in the diet. Perchlorate treatment induced the classic picture of primary hypothyroidism. Selenium deficiency increased thyroid hormone levels in perchlorate-treated rats and in controls drinking tap water. In the latter group, it also decreased TSH plasma concentration and thyroid weight. These effects were partially reversed by Se supplementation. In vitro experiments, performed on adult rats, revealed increased radioiodide uptake and organification in glands from the rats submitted to the selenium-free diet. Plasma T3 half-life was similar in control and Se-deficient rats. These data suggest a higher efficiency of thyroid hormone synthesis in the thyroids of selenium-deficient rats, despite a lower thyroid stimulation as evaluated by serum TSH. They are compatible with the hypothesis that decreased selenium supply, leading to a decreased GSH-Px in the thyroid, increases hydrogen peroxide steady state level and thus thyroid peroxidase activity and thyroid hormone synthesis.

Regulation of plasma 1,25-(OH)2-D3 by phosphate: evidence against a role for total or acid-soluble renal phosphate content.

In order to evaluate a possible role for tissue phosphate or phosphorylated compounds in mediating the increase in plasma 1,25-(OH)2-D3 levels during dietary phosphate deprivation, measurements of total and acid-soluble renal cortical phosphate content have been made in both intact and hypophysectomized (hypox) rats eating a normal diet and also after four days of dietary phosphate deprivation. Similar measurements were also made in phosphate-deprived hypophysectomized rats replaced with growth hormone (GH). Total and acid-soluble renal cortical phosphate content averaged 81 +/- 8 mumol/g and 4.1 +/- 0.6 mumol/g, respectively, in intact rats eating the normal diet and were not significantly altered after phosphate deprivation despite a fall in plasma phosphate of about 40% and a fourfold increase in plasma 1,25-(OH)2-D3 levels. Total and acid-soluble renal cortical phosphate content levels were higher in hypox rats, averaging 92 +/- 8 mumol/g and 4.9 +/- 0.7 mumol/g, respectively, but also did not change after phosphate deprivation. Replacement of phosphate-deprived hypox rats with GH resulted in a further fall in plasma phosphate and a significant increase in plasma 1,25-(OH)2-D3 levels, but there was no change in either total or acid-soluble renal cortical phosphate content. The distribution of organophosphorus compounds in the acid-soluble phosphate fraction in these experiments was also evaluated using 31P NMR spectrometry. Although there appeared to be an increase in the total concentration of organophosphorus compounds after phosphate deprivation, this effect was not altered by hypophysectomy or by replacement of phosphate-deprived hypox rats with GH.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting uptake and retention of technetium-99m-diphosphonate and 99m-pertechnetate in osseous, connective and soft tissues.

The bone scanning complex, 99mTc-Sn-EHDP, consisting of the nuclide technetium-99m, stannous ion and ethane-1-hydroxy-1,1-diphosphonate, administered intravenously is retained in soft tissues in proportion to increasing calcium content of the tissues. Within bone tissue, the retention is proportional to vascularity and to surface area of calcium phosphate in bones and not necessarily to calcium and phosphate concentration. The nuclidic agent 99mTcO4-BUT NOT THE 99MTc-diphosphonate is selectively taken up by the thyroid and this uptake can be blocked by administering sodium perchlorate. Among the connective tissues studied, the tracheal cartilage seems to have the greatest potential to calcify with increasing age of the animal and man. Soft tissue does not retain the bone scanning complex 99mTc-Sn-EHDP but does retain 99mTcO4-.