The Effect of Sodium Bromide on Thyroid Function. In: Chambers PL, Chambers CM, Dirheimer G, editors. The Target Organ and the Toxic Process. Berlin: Springer Berlin Heidelberg; 1988. pp. 93-7. [DOI: 10.1007/978-3-642-73113-6_14]

Influence of medications on thyroid function in dogs: An update

Erroneous thyroid function test results can occur because of drugs that alter thyroid hormone physiology in one or more aspects, including synthesis, secretion, distribution, and metabolism. Research since publication of the last review in the Journal of Veterinary Internal Medicine (JVIM) 20 years ago has evaluated the effects of amiodarone, zonisamide, inhalant anesthetics, clomipramine, trilostane, and toceranib on thyroid function tests in the dog. In addition, recent work on the effects of glucocorticoids, sulfonamides, phenobarbital, and nonsteroidal anti-inflammatory drugs will be reviewed. Awareness of these effects is necessary to avoid misdiagnosis of hypothyroidism and unnecessary treatment.

Development of radiometric assays for quantification of enzyme activities of the key enzymes of thyroid hormones metabolism

We newly elaborated and adapted several radiometric enzyme assays for the determination of activities of the key enzymes engaged in the biosynthesis (thyroid peroxidase, TPO) and metabolic transformations (conjugating enzymes and iodothyronine deiodinases, IDs) of thyroid hormones (THs) in the thyroid gland and in peripheral tissues, especially in white adipose tissue (WAT). We also elaborated novel, reliable radiometric methods for extremely sensitive determination of enzyme activities of IDs of types 1, 2 and 3 in microsomal fractions of different rat and human tissues, as well as in homogenates of cultured mammalian cells. The use of optimized TLC separation of radioactive products from the unconsumed substrates and film-less autoradiography of radiochromatograms, taking advantage of storage phosphor screens, enabled us to determine IDs enzyme activities as low as 10(-18) katals. In studies of the interaction of fluoxetine (Fluox) with the metabolism of THs, we applied adapted radiometric enzyme assays for iodothyronine sulfotransferases (ST) and uridine 5'-diphospho-glucuronyltransferase (UDP-GT). Fluox is the most frequently used representative of a new group of non-tricyclic antidepressant drugs--selective serotonin re-uptake inhibitors. We used the elaborated assays for quantification the effects of Fluox and for the assessment of the degree of potential induction of rat liver ST and/or UDP-GT enzyme activities by Fluox alone or in combination with T(3). Furthermore, we studied possible changes in IDs activities in murine adipose tissue under the conditions that promoted either tissue hypertrophy (obesogenic treatment) or involution (caloric restriction), and in response to leptin, using our newly developed radiometric enzyme assays for IDs. Our results suggest that deiodinase D1 has a functional role in WAT, with D1 possibly being involved in the control of adipose tissue metabolism and/or accumulation of the tissue. Significant positive correlation between specific enzyme activity of D1 in WAT and plasma leptin levels was found. The newly developed and adapted radiometric enzyme assays proved to be very useful tools for studies of factors modulating THs metabolism, not only in model animals but also in clinical studies of human obesity.

Effect of anticonvulsant dosages of potassium bromide on thyroid function and morphology in dogs

A placebo-controlled experiment was performed to evaluate the effect of potassium bromide on the canine thyroid gland. Basal total thyroxine, free thyroxine, and basal thyrotropin serum concentrations were evaluated over a 6-month period in potassium bromide-treated and control dogs. A thyrotropin-releasing hormone stimulation test was also performed in all dogs at the beginning and conclusion of the study. Thyroid histopathology was compared between treated and control dogs at the end of the study. No difference was detected in any parameter between the two groups at the end of the study. A decline in thyroid hormone concentrations over the course of the study did occur in both groups of dogs. Potassium bromide does not appear to have a significant effect on canine thyroid function or morphology.

Impact of high bromide intake in the rat dam on iodine transfer to the sucklings

A significant impact of high bromide levels in the organism of the mother on iodine transfer to the sucklings was established in experiments with female Wistar rats. The observed decrease in iodine transfer to the young through mothers' milk and/or an increase in the bromide concentration in the milk, caused a decrease in body weight of the pups. Enhanced bromide levels also adversely affected the thyroid gland of the young. High bromide intake in the lactating dams caused a decrease in iodide accumulation in the mammary glands, and also an increase in iodide elimination through the kidneys.

Long-term action of potassium bromide on the rat thyroid gland

Male rats fed by a standard diet with determined of bromine and iodine content were exposed to a 133-day oral administration of KBr (100, 200, 400 mg Br-/l drinking water). Their thyroid glands showed increased growth of the epithelial cells reflected by a microfollicular rearrangement of the parenchyma due to proliferation of very small follicles with a low or zero content of colloid. Morphometric analysis of thyroids of Br(-)-exposed animals revealed a significant decrease in the volume of intrafollicular colloid and marked increase in the number of the smallest follicles (areas up to 100 and 100-300 micron 2). In addition, the nuclei of thyrocytes showed an increased number of mitoses. The vascularization was increased as well. In the blood plasma of the Br(-)-exposed animals the T4 concentration was significantly decreased in dependence on the bromine concentrations. Thyroglobulin immunoreactivity in the colloid of Br(-)-exposed animals decreased after administration of 400 mg Br-/l drinking water. Increasing concentrations of Br- in the drinking water caused an increased bromine concentration in the thyroid, a decreased iodine content and a decreased I/Br molar ratio. The changes in the rat thyroid caused by long-term administration of 100 mg Br-/l were similar to hyperplastic parenchymal goitre and were comparable to those induced in previous experiments by the same bromine concentration administered over a 16- and 66-day period respectively.

Potassium bromide and the thyroid gland of the rat: morphology and immunohistochemistry, RIA and INAA analysis

The increasing environmental concentration of bromine has resulted in attempts to obtain information on its possibly deleterious effect on humans, particularly on a major target organ of this halogen i.e. the thyroid gland. In order to establish the morphological and functional effects of bromine on the thyroid, we have performed experiments on male rats which, in addition to a standard diet with an estimated iodine/bromine content, were fed for periods of 16 and 66 days with the small quantities of bromide expected to be encountered in the environment (10, 50 and 100 mg of Br-/l in drinking water). This treatment induced growth of the follicular epithelial component and microfollicular tissue rearrangement, a reduction of intrafollicular colloid, an increase in the height of the follicular cells and the number of mitoses, and it enhanced vascularization. Image analysis revealed a significant reduction in the volume of colloid, despite the accompanying rise in the number of minute follicles. The immunohistochemical positivity of the thyroglobulin fell in the microfollicular colloid of the exposed animals, although this was affected to a lesser extent in the larger follicles. The concentration of bromine in the thyroid increased with the amount of bromine intake, while at the same time the molar ratio of iodine/bromine decreased. The plasma level of T4 was lowered after both 16 and 66 days of treatment, but the T3 level only after 66 days treatment. The level of TSH did not exhibit any significant change. The observed changes, which have a parenchymatous goitre-like character, may have a direct relevance for human medicine, since the concentrations of bromide chosen in these experiments are readily encountered in the environment.

Effect of enhanced bromide intake on the concentration ratio I/Br in the rat thyroid gland

Interaction of bromine with iodine was studied in the rat thyroid gland under the conditions of different bromide intake. Bromine and iodine in the thyroid dry weight were determined by instrumental neutron activation analysis (INAA). It was found that with increased bromide intake the bromine concentration in the thyroid gland increased with simultaneous decrease in the iodine concentration. The change in the I/Br concentration ratio depends on a number of halogen binding positions and on the bromide supply. The I/Br parameter reacts sensitively to the changes of bromide intake already in the region of low bromine concentration levels.

Bromine and thyroid hormone activity

AIMS

To examine the possible consequences of high plasma concentrations of bromine on thyroid hormone.

METHODS

Bromine was measured by inductively coupled plasma mass spectrometry in the plasma of 799 patients consulting for thyroid disorders. Because the mean (SD) bromine concentration in the plasma of healthy subjects is 4 (1) mg/l, concentrations above 6 mg/l were regarded as outside the normal range. Bromine, free thyroxine (FT4), and thyroid stimulating hormone (TSH) values were compared.

RESULTS

The percentage of patients with normal, low, and high FT4 and TSH plasma activities, measured separately, did not differ between patients with low and high bromine concentrations. The percentage of patients with high TSH but normal FT4 values was significantly higher in the group with bromine values of more than 6 mg/l than in the group with bromine concentrations below this (p < 0.02).

CONCLUSION

An increase in plasma bromine could potentiate an increase in plasma TSH concentration, probably as a consequence of a minor inhibitory effect on thyroid activity.

Effects of thyroparathyroidectomy on the distribution of bromine and iodine in rat tissues

The concentrations of iodine (I) and bromine (Br) were measured by inductively coupled plasma mass spectrometry in the plasma, kidney, heart, liver, and brain of control and thyroparathyroidectomized (TPTX) rats without and with an additional intake of either NaI or NaBr, 0.5 and 5 mumol/kg/d, respectively, for 21 d. In all groups, the highest concentrations of I and Br were found in the plasma. TPTX did not modify the concentrations of I in tissues, but slightly increased Br in plasma (+33%) and kidney (+24%). The additional intake of I with the drink induced an increase of I concentrations in the tissues tested (from 54 to 191%), except brain, both in control and TPTX rats. This additional intake of I also increased Br levels in the plasma of control (+24%) and TPTX rats (+53%). The additional intake of Br with the drink induced an increase of Br levels in all the tested tissues, brain included (from 85 to 284%). The augmentation was higher in the tissues, particularly brain, of TPTX rats than of controls. The increase of Br in brain after an additional intake contrasts with the absence of increase of I given in the same conditions. This difference between I and Br probably results from the smaller radius of Br ion in comparison with I ion radius. In conclusion, TPTX did not modify the distribution of I in the tested tissues, but slightly increased the concentrations of Br in plasma and kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of high-performance liquid chromatographic detection methods for thyronine and tyrosine residues in toxicological studies of the thyroid

Four high-performance liquid chromatographic methods for the detection of thyroid hormones (iodinated thyronines) and precursors (iodinated tyrosines) have been developed and evaluated. Two methods consist of direct determination of the parent compounds with detection at ultraviolet wavelength (230 nm) and with electrochemical detection. The two other methods consist of a pre-column derivatization (with fluorenylmethyl chloroformate and dabsyl chloride) prior to high-performance liquid chromatographic analysis. The various methods were evaluated based on their practical use and sensitivity. The method with direct ultraviolet detection turned out to be the most practical method. With this method analyses of thyroid homogenates have been performed from rats from a toxicological experiment.

Peroxidase-catalyzed bromination of tyrosine, thyroglobulin, and bovine serum albumin: comparison of thyroid peroxidase and lactoperoxidase

A recent paper (Buchberger, W., 1988, J. Chromatogr. 432, 57) on lactoperoxidase-catalyzed bromination of tyrosine and thyroglobulin stated, without evidence, that thyroid peroxidase (TPO) is able to use bromide as a substrate. This was in disagreement with unpublished experiments previously performed in this laboratory, and we undertook, therefore, to examine this subject further. Highly purified porcine TPO was compared with lactoperoxidase (LPO) and chloroperoxidase (CPO) for ability to catalyze bromination of tyrosine, thyroglobulin, and bovine serum albumin (BSA). The incubation mixture contained 50-100 nM peroxidase, 10-500 microM 82Br-, tyrosine (150 microM), thyroglobulin (0.3 or 1 microM), or BSA (7.5 microM), and a source of H2O2. The latter was either generated by glucose (1 mg/ml)-glucose oxidase (0.5 or 1 micrograms/ml), or added initially as a bolus (100 microM). With TPO, formation of organically bound 82Br was undetectable under all conditions in the pH range 5.4-7.0. Lactoperoxidase and CPO, on the other hand, displayed considerable brominating activity. Lactoperoxidase was much more active at pH 5.4 than at pH 7.0 and was more active with BSA as acceptor than with tyrosine or thyroglobulin. The distribution of 82Br among the various amino acids in LPO-brominated thyroglobulin and BSA was determined by HPLC. As expected, monobromotyrosine and dibromotyrosine together comprised the greatest part of the bound 82Br. However, a surprisingly high percentage (20-25%) was present as monobromohistidine. Evidence was also obtained for the presence of a small percentage of the bound 82Br as tetrabromothyronine. Peroxidase-catalyzed bromination probably depends on the oxidation of Br- to Br+ by the Compound I form of the enzyme. Since oxidation of Br- to Br+ requires a stronger oxidant than oxidation of I- to I+, our results suggest that Compound I of LPO and of CPO has a higher oxidation potential than Compound I of TPO. In vivo experiments with rats on a low iodine diet injected with 82Br- showed that even under conditions of high stimulation by thyrotropic hormone, there is negligible formation of organic bromine in the thyroid. Measurements of thyroid:serum concentration ratios for 82Br- in similar rats provided no evidence that Br- is a substrate for the iodide transport system of the thyroid.

Determination of proteolytic hydrolysis of thyroglobulin

A method for the determination of the free thyronine- and tyrosine-like amino acids in the thyroidal protein thyroglobulin is presented. The compounds of interest are monoiodotyrosine, diiodotyrosine, thyronine, diiodothyronine, triiodothyronine and tetraiodothyronine. The extent of proteolysis was followed by high-performance liquid chromatographic monitoring of both the remaining peptides and the formation of the free thyroidal amino acids. Total hydrolysis was achieved by a combination of proteolytic enzymes. A number of enzymes were tested, such as trypsin, chymotrypsin, pronase, aminopeptidase-M, carboxypeptidase-A, carboxypeptidase-P and carboxypeptidase-Y. The best combination turned out to be pronase followed by aminopeptidase-M. The relative amounts of the enzymes, with respect to the substrate thyroglobulin, and the time of incubation were optimized to achieve total proteolysis in 4 h. The method was applied successfully to samples from a toxicological experiment with sodium bromide.