Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “IODIDES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed1976

Inhibition of thyroglobulin biosynthesis and degradation by excess iodide. Synergism with lithium.

Lithium and excess iodide inhibit the release of thyroid hormone from preformed stores. We thus tested the hypothesis that this was due to an inhibition of thyroglobulin breakdown. Rats were pre-treated with propyl-thiouracil (PTU) for 3 weeks in order to deplete their thyroids of thyroglobulin. While the PTU was continued, lithium chloride (0.25 mEq./100 g weight) or potassium iodide (3 mg per rat) were injected every 12 h for d days. Thereafter the thyroglobulin content in thyroid gland homogenates was measured. PTU pre-treatment lowered the thyroglobulin content from 4.21 to 0.22 mg/100 mg gland. Lithium caused a marked re-accumulation of thyroglobulin to 0.60 mg/100 mg within 3 days. While iodide alone had only a borderline effect, it markedly potentiated the action of lithium and a combination of the two drugs increased the thyroglobulin content to 1.04 mg/100 mg. Thyroxine was injected into similarly pre-treated animals to suppress secretion of thyrotrophic hormone. This markedly inhibited the proteolysis of thyroglobulin and 1.3 mg/100 mg gland accumulated after 3 days. Excess iodide, given in addition to thyroxine, decreased the amount of thyroglobulin accumulated to 0.75 mg/100 mg gland. To study whether this could be explained by an inhibitory action of iodide on thyroglobulin biosynthesis, thyroid glands from animals treated with excess iodide were incubated in vitro in the presence of 0.2 mM iodide for 3 h. Iodide decreased the incorporation of radioactive leucine into total thyroidal protein and into thyroglobulin by 25 and 35% respectively. Iodide did not inhibit protein synthesis in the kidney, liver or muscle tissue. Thus, large doses of iodide selectively inhibit thyroglobulin biosynthesis.

Animals↗
PubMed1987

Differential modulation by Ca2+ of iodide transport processes in a cultured rat thyroid cell strain.

The interrelationship between the roles of Ca2+ and cyclic AMP (cAMP) in the control of intracellular iodide accumulation was investigated in the continuous rat thyroid cell strain FRTL-5. Using incubation conditions designed to allow independent study of iodide uptake and efflux into the incubation medium, dibutyryl cAMP (dbcAMP) mimicked the effect of TSH in enhancing iodide uptake, but the responses to both stimulators were decreased in the presence of the Ca2+ ionophore A23187, although the ionophore was ineffective when addition was delayed until after withdrawal of the stimulators. L-Adrenaline, an alpha-adrenergic agonist inactive with respect to cAMP accumulation in this cell strain, was also inactive with regard to iodide uptake. The rapid efflux of iodide from FRTL-5 cells seen in response to TSH was not mimicked by dbcAMP, but was reproduced by A23187, providing evidence for the involvement of Ca2+ in the release process. Under the latter conditions, no additional effect of TSH was obtained. L-Adrenaline also stimulated iodide efflux, in support of a possible role of alpha-adrenergic agonists in controlling the apical membrane p presentation of iodide in vivo. The observed differential effects of dbcAMP and alpha-adrenergic agonists on iodide uptake and efflux respectively, provide further evidence for the existence of two functionally distinct mechanisms controlling the available level of intracellular iodide. Opposing effects of free intracellular Ca2+ may, however, serve to control the activities of both influx and efflux processes since, whilst experimental increments in Ca2+ appear to promote iodide efflux through a non-cAMP-mediated pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

[Urinary iodide determination by X-ray fluorescence].

Urinary iodide measurement has been carried out by X-ray-fluorescence, either directly on urinary solution, or after matrix concentration. Proportionality between emitted XK alpha rays of iodine and iodide mass in standards has been observed on a large scale, ranging up to 400 micrograms. With an exciting-1.11 GBq (241(95) Am)-radioactive source, 0.44 microgram are detected for solid matrix, and 0.9 microgram/ml for iodide in solution for 10 mn measuring time. So direct measurement on solution can be applied only to high excreted iodide. For normal range iodide determination is performed after anionic resin concentration (on 100 ml or 200 ml). For tracing, Na I131 is employed. The binding ratio is strongly depending on flow, resin weight, and associate urinary anionic components. On 20 healthy subjects, normal range value is 53 +/- 22 micrograms/l (m +/- s.d.). Comparative study with an electrochemical method showed fluorescence iodide values are lower than the former. The proposed method is very simple, one or two steps (function of iodide content). As no interfered Rx has been observed in the Rx iodide region, the authors can ascertain that accurate values are observed by X-ray fluorescence. In case of high iodide content, this methods allows to distinguish urinary iodide versus total urinary iodine, when performing solution and matrix concentration studies on the urinary batch.

Humans↗
PubMed1989

Mechanism of horseradish peroxidase-catalyzed conversion of iodine to iodide in the presence of EDTA and H2O2.

EDTA not only blocks the horseradish peroxidase (HRP)-catalyzed iodide oxidation to I-3 but also causes an enzymatic conversion of oxidized iodine species to iodide (Banerjee, R. K., De, S. K., Bose, A. K., and Datta, A. G. (1986) J. Biol. Chem. 261, 10592-10597). The EDTA effect on both of these reactions can be withdrawn with a higher concentration of iodide and not with H2O2. Spectral studies indicate a possible interaction of EDTA with HRP as evidenced by the formation of modified compound 1 with H2O2 at 416 nm instead of 412 nm in the absence of EDTA. EDTA causes a hypochromic effect on HRP at 402 nm which undergoes the bathochromic red shift to 416 nm by H2O2. The addition of iodide to the 416 nm complex causes the reappearance of the Soret band of HRP at 402 nm. Among various EDTA analogues tested, N-N-N'-N'-tetramethylethylenediamine (TEMED) is 80% as effective as EDTA in the conversion of I-3 to iodide and produces a spectral shift of HRP similar to EDTA. Interaction of EDTA with HRP is further indicated by the hyperchromic effect of HRP and H2O2 on the absorption of EDTA at 212 nm. The addition of oxidized iodine species produces a new peak at 230 nm due to formation of iodide. EDTA at a higher concentration can effectively displace radioiodide specifically bound to HRP indicating its interaction at the iodide-binding site. The enzyme, after radioiodide displacement with EDTA, shows a characteristic absorption maximum at 416 nm on the addition of H2O2, indicating that EDTA is bound with the enzyme. Both positive and negative circular dichroism spectra of HRP and the HRP.H2O2 complex, characteristic of heme absorption, are altered by EDTA, suggesting an EDTA-induced conformational change at or near the heme region. This is associated with a change of affinity of heme toward H2O2 and azide. It is postulated that EDTA interacts at the iodide-binding site of the HRP inducing a new conformation that blocks iodide oxidation but is suitable to convert iodine to iodide by a redox reaction with H2O2.

Catalysis↗
PubMed2003

Nonradioactive iodide effectively induces apoptosis in genetically modified lung cancer cells.

We assessed a nonradioactive approach to induce apoptosis in non-small cell lung cancer by a novel iodide uptake and retention mechanism. To enhance tumor apoptosis, we transduced non-small cell lung cancer cells with retroviral vectors containing the sodium iodide symporter (NIS) and thyroperoxidase (TPO) genes. Expression of NIS and TPO facilitated concentration of iodide in tumors. As a consequence of the marked increase in intracellular levels of iodide, apoptosis was seen in >95% of NIS/TPO-modified lung cancer cells. Intraperitoneal injection of potassium iodide resulted in significant tumor volume reduction in NIS/TPO-modified tumor xenografts without apparent adverse effects in SCID mice. Iodide induced an increase in the level of reactive oxygen species. Iodide-induced apoptosis is sensitive to N-acetylcysteine inhibition, suggesting an important role by reactive oxygen species in this apoptotic process. In addition, iodide-induced apoptosis is associated with overexpression of CDKN1A (p21/Waf1)and down-regulation of survivin at both mRNA and protein levels. This is the first report demonstrating that a therapeutic dose of nonradioactive iodide has potent efficacy and high selectivity against lung cancer when used in combination with genetic modification of cancer cells to express the NIS/TPO genes.

Acetylcysteine↗
PubMed1991

Hydrogen peroxide inhibits iodide uptake and iodine organification in cultured porcine thyroid follicles.

We investigated the effect of hydrogen peroxide on the process of thyroid hormone formation in a physiologic culture system of porcine thyroid follicles that we recently established. Porcine thyroid follicles cultured in medium containing 1 mU/mL TSH were exposed to 0 to 500 microM hydrogen peroxide in the presence of 0.1 microCi carrier-free Na125 and sodium iodide for 2 h. Iodide uptake and iodine organification were measured in this incubation system. The kinetics of iodide uptake were used to explain the action of hydrogen peroxide. In addition, cAMP content and Na+,K(+)-ATPase activity (an enzyme necessary for iodide uptake) were measured to investigate the mechanism of hydrogen peroxide action. Hydrogen peroxide at concentrations of 100, 200, and 500 microM inhibited iodide uptake in a dose-dependent manner. Iodide organification was inhibited only when the concentration of hydrogen peroxide was greater than 200 microM. The kinetics of iodide uptake indicated that hydrogen peroxide was a noncompetitive inhibitor with iodide. Inhibition of iodide uptake and iodine organification by hydrogen peroxide were not mediated by alteration of cAMP content of Na+,K(+)-ATPase activity, since exposure to even 500 microM hydrogen peroxide did not change these parameters in the follicle when compared with those of control samples. Our results suggest that the iodide transport system in the thyroid follicle is inhibited at 200 microM hydrogen peroxide or greater.

Analysis of Variance↗
PubMed1997

Characteristics of the prolactin stimulation of iodide uptake into mouse mammary gland explants.

We have recently reported that prolactin (PRL) stimulates iodide uptake into cultured mouse mammary tissues. This effect occurs in both TCA soluble and insoluble tissue fractions. The effect of PRL apparently involves an RNA-DNA-dependent mechanism, since actinomycin D and cyclohexamide abolish the PRL stimulation of iodide uptake and its incorporation into protein. Perchlorate and thiocyanate, inhibitors of the iodide transporter, also abolish the PRL effects on iodide uptake and incorporation. Similarly, propylthiouracil and aminotriazole, inhibitors of peroxidase, abolish both effects of PRL. Finally, the extent of iodide uptake in mammary cells is suppressed by about 50% in sodium-free medium. These studies thus suggest the existence of a sodium-iodide symporter in the mammary gland which has characteristics similar to the iodide transporter in the thyroid gland-that is, it is sodium dependent and is inhibited by perchlorate and thiocyanate. The fact that both iodide transporter inhibitors and peroxidase inhibitors abolish PRL-stimulated iodide uptake and incorporation suggests that there may be a coupled mechanism involving the iodide transporter and the peroxidase enzyme.

Amitrole↗
PubMed1993

Evidence that the inhibitory effects of iodide on thyroid cell proliferation are due to arrest of the cell cycle at G0G1 and G2M phases.

The thyroid gland is unique in its ability to respond to ambient levels of iodine to autoregulate thyroid function and, possibly, thyroid cell proliferation. Although the inhibitory effects of iodide on thyroid cell proliferation have been previously reported, the exact mechanism and site of action of iodide on cellular proliferation events are poorly understood. Our initial experiments established the optimal cell plating density and timing to achieve exponential cell growth of FRTL5 thyroid cells, and subsequent studies using flow cytometric DNA analysis established the normal cell cycle kinetics of FRTL5 thyroid cell proliferation. FRTL5 cells were then exposed to graded concentrations of sodium iodide to establish whether the inhibitory effects of iodide are mediated through specific cell cycle events. We observed that increasing concentrations of iodide inhibited FRTL5 thyroid cell proliferation. Analysis of the cell cycle revealed two specific effects of iodide on cell cycle kinetics. The first was an arrest of cells in G0G1, evidenced by an accumulation of cells in this phase and a concomitant reduction in the percentage of cells in the S-phase. The second was an arrest of cells in the G2M phase of the cycle. G0G1 and G2M arrest occurred within 24 h and then reached a plateau. Iodide exposure did not increase the number of cells undergoing necrosis. The addition of methimazole at two concentrations (0.2 and 2 mM) to cells exposed to 100 mM NaI prevented the accumulation of cells in G2M, but did not abolish the accumulation of cells in G0G1 or the reduction in cell number. These results indicate that the inhibitory effects of iodide on FRTL5 thyroid cell proliferation are mediated by its action at two critical regulating points of the cell cycle, G0G1 and G2M. It appears that organified iodine may mediate the cell cycle arrest in the G2M phase, whereas inorganic iodide may be responsible for the inhibitory effects at G0G1.

Animals↗
PubMed1993

Propranolol has direct antithyroid activity: inhibition of iodide transport in cultured thyroid follicles.

The effect of propranolol on the process of thyroid hormone formation was studied in a physiological culture system. Porcine thyroid follicles were preincubated with propranolol for 24 h. Iodide transport, iodine organification, and de novo thyroid hormone formation were measured by incubating these follicles with the mixture of carrier-free 0.1 microCi Na125I and 50 nM NaI for 2 to 6 h at 37 degrees C. A concentration of propranolol greater than 100 microM inhibited iodide transport in a dose-dependent manner; this inhibition was non-competitive with iodide and independent of thyrotropin (TSH). Reduced iodine organification and thyroid hormone formation was seen with 150 microM propranolol or greater. The inhibitory action of propranolol was not caused by beta-blocking activity, since D-propranolol (devoid of beta-blocking activity) inhibited iodide transport, and other beta-blockers (metoprolol, atenolol, and labetalol) did not inhibit iodide transport. The inhibition of iodide transport was most likely caused by membrane stabilizing activity since quinidine, which possesses the same membrane stabilizing activity as propranolol, also inhibited iodide transport. TSH-mediated cAMP generation and Na+K+ ATPase activity, membrane functions for iodide transport, were unaffected by propranolol. Our study has shown, for the first time, that propranolol has a direct antithyroid action, namely inhibition of iodide transport in the intact thyroid follicle.

Adrenergic beta-Antagonists↗
PubMed1976

Increased uptake of iodide by hormone-responsive compared to hormone-independent mammary tumors in GR mice.

The uptake of 125-iodide by transplanted hormone-responsive (HR) or hormone-independent (HI) mammary tumors, normal mammary tissue and skeletal muscle was compared in GR mice. The uptake of 125-iodide by HR mammary tumors in mice treated with progesterone and oestrone (P+O) was about 20 times greater than the uptake of 125-iodide by HI mammary tumors in mice not treated with P+O. This difference in uptake of 125-iodide by HR and HI mammary tumors could not be attributed to the difference in the hormonal status of the mice since uptake of 125-iodide was also low in HI tumors in mice receiving P+O treatment. The uptake of 125-iodide by HR mammary tumors was greatly reduced by the simultaneous injection of either an excess of non-radioactive iodide or of perchlorate. Uptake of 125-iodide by normal mammary tissue and skeletal muscle was similar was similar in all groups of tumor bearing mice, and was not influenced by the presence of an excess of non-radioactive iodide or of perchlorate. The possible clinical significance of these findings is discussed.

Adenocarcinoma↗
PubMed2004

Linearity and reversibility of iodide adsorption on sediments from Hanford, Washington under water saturated conditions.

A series of adsorption and desorption experiments were completed to determine the linearity and reversibility of iodide adsorption onto sediment at the Hanford Site in southeastern Washington. Adsorption experiments conducted with Hanford formation sediment and groundwater spiked with dissolved (125)I (as an analog tracer for (129)I) indicated that iodide adsorption was very low (0.2 mL/g) at pH 7.5 and could be represented by a linear isotherm up to a total concentration of 100 mg/L dissolved iodide. The results of desorption experiments revealed that up to 60% of adsorbed iodide was readily desorbed after 14 days by iodide-free groundwater. Because iodide adsorption was considered to be partially reversible, even though small amount of initial iodide is retarded by adsorption at mineral-water interfaces, the weak adsorption affinity results in release of iodide when iodide-free pore waters and uncontaminated groundwaters contact the contaminated sediments in the vadose zone and aquifer systems.

Adsorption↗
PubMed1995

Methodology for assaying iodide conductance in proteoliposomes: specific induction by thyroid membrane protein.

A sensitive assay is developed to assess the existence of an iodide channel in a fraction of solubilized membrane proteins. This step is critical when considering various procedures for purification of this channel. Sodium cholate is used as a detergent as it does not denature the iodide channel. A simple and rapid method involving gel-filtration chromatography is used simultaneously to remove the detergent and to adjust the buffer composition, before protein insertion into liposomes. The presence of an iodide channel is investigated by measuring the iodide conductance of these proteoliposomes at 4 degrees C. An outward iodide gradient is set up across the proteoliposomal membrane by anion-exchange chromatography, allowing uptake of radiolabelled iodide. This uptake is conductive as it is abolished by valinomycin in the presence of potassium. It is specifically mediated by a thyroid plasma-membrane protein inserted into liposomes, as its denaturation before insertion totally abolished uptake. It was observed only within a well-defined fraction of thyroid membrane proteins collected by size-exclusion chromatography (molecular mass between 100 and 200 kDa). Furthermore, it was not observed with other membrane proteins such as ileal brush-border-membrane proteins or bacteriorhodopsin. Like many anion channels, this conductance was also inhibited by N-phenylanthranilic acid. Optimization of the assay is described, validating the measurement of conductive iodide uptake at 30 s by proteoliposomes reconstituted in a ratio of 10 micrograms of protein to 90 micrograms of lipid, with an outward iodide gradient (KI 15 mM inside and 1 microM outside). This assay provides a test of the biological activity of the iodide channel at each step of the purification; it can be applied to any anionic channel.

Animals↗
PubMed1977

Excess iodide and the accumulation of 125I by the thyroid, plasma and developing oocytes of the Japanese quail.

1. Developing oocytes of the Japanese quail accumulated 0-44 microgram of each 1 microgram of 125I-labelled iodide after intra-muscular injection of doses up to 500 microgram iodide as NaI but only 0-007 microgram after injection of more than this: the abrupt change in the rate of accumulation was attributed to saturation of the iodide transport mechanism. 2. The proportion of available iodide transferred into the oocytes appeared to be more dependent on the amount of iodide injected and the total weight of growing oocytes than on a requirement for either a store of iodide for the embryo or an iodide excretory pathway for the hen. 3. The thyroid was about four times more active in accumulating iodide than the oocyte. 4. The percentage of iodide accumulated by the plasma was the same at all dose rates.

Animals↗
PubMed1992

The iodide channel of the thyroid: a plasma membrane vesicle study.

The uptake of radioactive iodide or chloride by plasma membrane vesicles of bovine thyroid was studied by a rapid filtration technique. A Na(+)-I- cotransport was demonstrated. When this Na(+)-I- cotransport is inactive (i.e., at 4 degrees C and in the absence of Na+), an uptake of iodide above chemical equilibrium could be induced, driven by the membrane potential. The latter was set up by allowing potassium to diffuse into the membrane vesicles in the presence of valinomycin and of an inward K+ gradient. This potential difference (positive inside) induced the uptake of iodide (or other anion present). The data support the existence of two anionic channels. The first one, observed at low near-physiological iodide concentration (micromolar range), which exhibits a high permeability and specificity for iodide (hence called the iodide channel), has a Km of 70 microM. The other one appears similar to the epithelial anion channel as described by Landry et al. (J. Gen. Physiol. 90: 779-798, 1987); it is still about fourfold more permeable to iodide than to chloride and presents a Km of 33 mM. Under physiological conditions the latter channel would mediate chloride transport, and the iodide channel, which is proposed to be restricted to the apical plasma membrane domain of the thyrocyte, transports iodide from the cytosol to the colloid space.

Animals↗
PubMed2002

Effect of insulin on iodide uptake in mouse mammary gland explants.

Studies were carried out primarily to assess the role of insulin in regulating iodide uptake in the mammary gland. Using cultured mammary gland explants from virgin and pregnant mice (12-14 days into gestation), insulin (1 microg/ml) was shown to stimulate iodide uptake after a 2-day exposure period. The effect of insulin was manifested by itself, as well as in the presence of cortisol and prolactin. Optimal iodide uptake was observed when tissues were treated with all three lactogenic hormones (insulin, cortisol, and prolactin). In a time-course experiment, the effect of insulin alone was initially observed after a 10-hr treatment; the effect was maintained for 30 hr. In dose-response studies, 1 ng/ml insulin elicited a significant effect after 24 hr in culture; a maximal effect was achieved with 50-100 ng/ml insulin. The optimal cortisol concentration for a maximum stimulation of iodide uptake was 10(-7)M. In a quantitative Western blot analysis employing an antibody to the sodium-iodide symporter, insulin stimulated an upregulation of the transporter protein after a 4-, 8-, or 20-hr treatment with insulin. Perchlorate and thiocyanate abolished the insulin effect on iodide uptake, further suggesting that the insulin response occurs via a stimulation of the sodium-iodide symporter. Clearly, insulin is an important and essential hormone in the lactogenic hormone complex for regulating iodide uptake in the mammary gland, but maximal expression of iodide uptake is only expressed when all three lactogenic hormones are present.

Animals↗
PubMed2003

Pendrin transporter carries out iodide uptake into MCF-7 human mammary cancer cells.

Previous studies have shown that iodide is actively taken up into mammary alveolar epithelial cells and secreted into milk. In the present studies we demonstrate that 125I also accumulates in MCF-7 cells against a concentration gradient; distribution ratios of greater than 30 were achieved. Iodide uptake into MCF-7 cells is transient, with peak accumulations occurring in about 5 min. The iodide is rapidly metabolized, probably to iodine, and it then exits the cells. The iodide transporter identified in MCF-7 cells is pendrin. DIDS, a nonspecific inhibitor of anion exchange, inhibits iodide uptake. Iodide uptake is impaired at reduced temperature, but is not dependent on sodium. Inhibitors of the sodium-iodide symporter (NIS) as well as ouabain did not affect the extent of iodide uptake. The pendrin transporter but not NIS was identified via western blotting techniques. Pendrin appears to be the primary iodide transporter in the MCF-7 cell line stocks that were employed for these studies.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1979

Inhibition by iodide of the cholinergic stimulation of prostaglandin synthesis in dog thyroid.

Iodide is shown to inhibit the cholinergic stimulation of prostaglandin E2 (PGE2) and F2 alpha (PGF2 alpha) synthesis in dog thyroid slices. The inibitory effect of iodide was already detectable at 1 micron and reached its maximal level at 10 microns. At this concentration, iodide inhibited the carbamylcholine-stimulated release of PGE2 and PGF2 alpha by 59% and 73%, respectively (eight experiments). The effect of iodide was neither immediate nor rapidly reversed after a change of incubation medium. The unstimulated release of PGE2 and PGF2 alpha and the stimulation by epinephrine and ionophore A23187 were not modified by iodide in concentrations up to 0.1 mM. The effect of iodide was suppressed in the presence of methimazole (0.1 mM) but not NaClO4 (2 mM). Iodid (0.1 mM) did not inhibit the stimulation by carbamylcholine of PGF2 alpha and PGE2 release by rat pancreas in vitro. These data demonstrate a new action of iodide on the thyroid and establish a link among iodide metabolism, PG synthesis, and cholinergic action in the dog thyroid.

Animals↗
PubMed1982

Thyroid iodide compartments and their implication in the rat thyroid iodine organification.

To estimate the relative participation of transported and intrathyroidally generated iodide (internal iodide) in the iodination of newly synthesized and preexisting thyroglobulin (Tg) in the rat thyroid, the specific radioactivities (SRAs) of thyroid iodide, Tg, lysosomal iodine, and plasma hormones were followed for 92 h after radioactive iodide injection in intact or hypophysectomized rats. In control rats, the SRA of Tg and lysosomal iodine reached a maximum at 12 h. However, the SRA of lysosomal iodide was always smaller than that of Tg. In contrast, the SRA of hormonal iodide attained a maximum at 48 h. Thus, newly labeled iodine is endocytosed and mixed inside the lysosomes with older previously iodinated molecules; hormone secretion is mainly due to old labeled iodine (i.e. iodine with a high SRA from 48-96 h). These results are consistent with the presence of least two Tg compartments, with different turnover rates and hormone contents. On the other hand, in hypophysectomized rats, the SRA of Tg, lysosomes, and hormones showed only one maximum, at 24 h. Furthermore, the SRAs of Tg and lysosomes were similar at each time interval. It is inferred that in such rats, the old labeled iodine compartment is strongly reduced, and that inside the lysosomes, newly labeled iodine is predominant. Since in hypophysectomized rats, the recycling of iodide is abolished, it is concluded that in normal rats: 1) transported iodide is organified mainly by direct iodination of newly synthesized Tg, independently of TSH, and 2) internal iodide is organified mainly by delayed iodination of preexisting Tg, this process being TSH dependent.

Animals↗