Showing papers on "Iodine published in 1986"

The effect of iodide ingestion on the development of spontaneous lymphocytic thyroiditis in the diabetes-prone BB/W rat.

Abstract: It has been suggested that the incidence of Hashimoto's thyroiditis is increased in the presence of high iodide intake. The diabetes-prone BB/W rat develops spontaneous histological autoimmune lymphocytic thyroiditis (LT) without functional hypothyroidism between 60 and 120 days of age. Studies were carried out to determine whether iodine administration to BB/W rats would affect the incidence and severity of LT and induce hypothyroidism. Iodide (0.05% in water) or tap water (C) was administered ad libitum to 42 10-month-old BB/W rats and 71 30-day-old BB/W rats for 8 weeks. For control purposes, 0.05% iodide or tap water (C) was also administered ad libitum to 42 30-day-old nondiabetic and non-LT-prone BB/W genetically equivalent rats (W-line) for 12 weeks and 41 21-day-old Wistar rats for 7 weeks. In a separate experiment, weanling BB/W rats were fed a low iodine diet, a control iodine-sufficient (C) diet, or Purina chow (P) and tap water ad libitum for 8 weeks. In each experiment, blood was obtained at the time of death for the measurement of serum T4, T3, TSH, and antithyroglobulin antibody (anti-Tg Ab), and the thyroids were removed for histological evaluation (0 = no LT; 1-4 = LT). Iodide administration (0.05%) induced a significant increase in the incidence of LT in 30-day-old BB/W rats (I, 77%; C, 30%, P less than .001). Thyroid weight and serum T4, T3, and anti-Tg Ab concentrations were not affected by iodide administration. However, the presence of LT was associated with a significant increase in thyroid weight and anti-Tg Ab concentrations. BB/W rats subjected to a low iodine diet exhibited a significantly decreased incidence of LT (low I, 8.6%; C, 47.3%; P less than 0.01), but no statistically significant difference in anti-Tg Ab levels. Increased iodide intake did not significantly affect the incidence of LT in adult BB/W rats and did not induce LT or affect thyroid function in W-line or Wistar rats. These data show that iodine intake significantly affects the incidence of spontaneous LT in young, genetically predisposed rats.

Studies of hypothyroidism in patients with high iodine intake

Abstract: Twenty-two patients with spontaneously occurring primary hypothyroidism were studied to evaluate the spontaneous reversibility of the hypothyroid state Twelve (545%) became euthyroid after restriction of iodine intake for 3 weeks (reversible type) In the remaining 10 patients, thyroid function did not improve with restriction of iodine alone, and thus, replacement therapy was required, (irreversible type) In the reversible type, 1) radioactive iodine uptake after 1 week of restricted iodine intake was higher than in the irreversible type [500 +/- 122% (+/- SD) vs 43 +/- 32%; P less than 001], 2) the perchlorate discharge test was positive in 2 of 10 patients, and 3) the iodine-perchlorate discharge test, carried out in 7 of 8 patients with negative perchlorate discharge test, was positive in 6 Seven patients with the reversible type were given 25 mg iodine daily for 2-4 weeks; all became hypothyroid again Two patients had a history of habitual ingestion of seaweed (254 and 431 mg iodine, respectively), but the remaining 10 patients ingested ordinary amounts of iodine (1-5 mg) daily The patients with reversible hypothyroidism had focal lymphocytic thyroiditis changes in the thyroid biopsy specimen, whereas those with irreversible hypothyroidism had more severe destruction of the thyroid gland These results indicate the existence of a reversible type of hypothyroidism sensitive to iodine restriction and characterized by relatively minor changes in lymphocytic thyroiditis histologically Attention should be directed to this type of hypothyroidism, because thyroid function may revert to normal with iodine restriction alone

Iodine kinetic studies during amiodarone treatment.

Abstract: Iodine kinetic studies were performed serially in 15 patients taking 300 mg amiodarone/day for 6 months to assess the biological significance of the high iodine content of the drug. Urinary inorganic iodide excretion increased from 0.25 +/- 0.03 (+/- SE) mumol/mmol creatinine before treatment to over 7 mumol/mmol during therapy. Thyroid iodide clearance fell from 5.93 +/- 0.82 ml/min to less than 0.5 ml/min, while plasma inorganic iodide rose from 0.05 +/- 0.01 mumol/liter to approximately 2.2 mumol/liter during treatment. Thyroid absolute iodide uptake rose from 16.3 +/- 2.7 to 54.6 +/- 5.7 nmol/h after 6 weeks of therapy (P less than 0.001). Thereafter, it progressively declined, but it was still significantly elevated (32.0 +/- 4.3 nmol/h) after 24 weeks (P less than 0.01). The calculated daily excretion of inorganic iodide rose to over 80 mumol during the study, accounting for about 10% of amiodarone iodine. During this time, the patients all had the characteristic plasma thyroid hormone changes associated with amiodarone therapy, i.e. increased T4, free T4, and rT3 and decreased T3, while remaining clinically euthyroid. The massive increase in available inorganic iodide during amiodarone treatment is probably responsible for the induction of both the hypothyroidism and the thyrotoxicosis that can occur in patients receiving the drug.

Iodine Suppression of Iodide Uptake in FRTL-5 Thyroid Cells

Abstract: Exposure of FRTL-5 cells to iodide (I−) in excess of 3 μm suppresses the concentrative uptake of I− The depression of I− uptake measured at the steady state is due to a decrease in the rate of I− influx and not to an effect on I− efflux Exposure to Nal is associated with decreased T4 secretion and also depressed Na+-dependent amino acid accumulation The depression in I− and amino acid transports increases proportionately with the duration of exposure and concentration of I′ used but is not associated with alterations in FRTL-5 cell cAMP levels The I− suppression effect is blocked, however, when methimazole is present during the incubation with Nal In agreement with studies in vivo, I− suppression in FRTL-5 cells appears to depend on an intermediate in the organification process and to be independent of a TSH-induced cAMP-mediated action (Endocrinology 118: 2477–2482, 1986)

Short term administration of potassium perchlorate restores euthyroidism in amiodarone iodine-induced hypothyroidism.

Abstract: We studied the effect of potassium perchlorate (KCl04) in patients with hypothyroidism due to amiodarone. The short term administration of KClO4 to six such patients led to prompt restoration of euthyroidism, while the three untreated patients remained hypothyroid for 2-6 months. Since KCl04 inhibits thyroid iodide transport, thereby blocking further entrance of iodide into the thyroid and decreasing intrathyroidal iodide content, amiodarone-associated hypothyroidism is probably secondary to the inhibitory effect of excess intrathyroidal iodine on thyroid hormone synthesis.

In vitro culture of Vitis: the effects of light spectrum, manganese sulfate and potassium iodide on morphogenesis

Abstract: The effects of blue and red light, manganese sulfate concentration (100 and 5 μM), and potassium iodide (5 and 0 μM) on shoot and root production from subcultured shoots of the Vitis hybrid “Remaily Seedless” were studied. Shoot production was greater in blue light. It was increased by lowering the manganese sulfate concentration. The response to manganese in blue light was greatest when there was no potassium iodide addition. Root production was decreased by red light and lower manganese concentration. The effects of manganese, iodide and light spectrum on morphogenesis are discussed in relation to their known effects on IAA metabolism.

Uninhibited thyroidal uptake of radioiodine despite iodine excess in amiodarone-induced hypothyroidism.

Abstract: Iodine excess is associated with a low thyroidalradioiodine uptake due to dilution of the radioisotope by theincreased stable iodide pool. We studied thyroidal uptake ofradioisotopes in cardiac patients with iodine excess due to amiodarone treatment. 99mTc-pertechnetate scintigraphy was performedin 13 patients receiving long term amiodarone therapy.Five patients had a clearly visible thyroid gland, and 8 patientshad no or a very faint thyroid image. All patients with positivescans had an increased plasma TSH level, whereas all patientswith negative scans had a normal or absent TSH response toTRH. Thyroidal uptake and discharge of 123I were studied in 30other patients. Group I (n = 11) had normal plasma TSHresponses to TRH and no iodine excess, group II (n = 7) hadnormal TSH responses to TRH and excess iodine from metrizoateangiography in the previous month, group III (n = 7) hadnormal or decreased TSH responses to TRH while receivinglong term amiodarone therapy, and group IV (n = 5) hadincreased TSH respo...

The role of iodine in carcinogenesis.

Abstract: Iodine is an essential nutrient for the normal growth and development of humans and animals and is necessary for normal metabolism and regulation of thyroid hormones. Iodine excess can produce thyrotoxicosis but not cancer. However, radioiodine is carcinogenic for the thyroid gland. Dietary iodine deficiency is associated with goiter in humans and animals. The goiter develops because of a feedback system between thyroid hormones, the pituitary gland, and the hypothalamus, and it regulates the synthesis and release of thyroid-stimulating hormone. Chronic hypersecretion of thyroid-stimulating hormone causes profound goiter (diffuse thyroid hyperplasia)‚ which appears to be related to carcinogenesis. Chronic dietary iodine deficiency in rats leads to thyroid follicular adenomas by 12 months and follicular carcinomas by 18 months. An increased risk of thyroid cancer has been reported in humans with goiter and those living in some iodine-deficient areas of the world. In very recent animal studies, iodine deficiency, chemical goitrogens, and thyroid toxins have been shown to have potent tumor-promoting effects. In rats, iodine deficiency is a much more effective tumor promoter than it is a carcinogen, suggesting that a similar relationship may exist in human populations. These studies suggest that a major role of iodine is to prevent the formation of thyroid tumors in humans and animals.

Endemic goitre in Finland and changes during 30 years of iodine prophylaxis.

Abstract: Endemic goitre of moderate severity was mainly found in the East of Finland still in the 1950s but the whole country was moderately iodine deficient. The daily iodine intake determined both from food consumption and from the urinary excretion in population samples was 50-70 micrograms being lower in the East. The main iodine sources were milk products, about 50% of the daily intake being derived from these. Iodized salt was available but its use was very low and the iodine content insufficient so that only about 20% came from this source. In the late 1950s iodine prophylaxis was activated and since then only salt containing 25 mg KI/kg has been imported. However, during the last decades the consumption of salt has declined from 7-8 g to less than 4 g per day. Today the iodine intake in Finland is about 300 micrograms per day, the highest in Europe. The main sources are milk products and eggs which provide about 2/3 of the daily iodine intake due to an active iodine prophylaxis of house animals and only 20% comes from iodized salt. The origin of endemic goitre in Finland has obviously been multifactorial autoimmunity, natural goitrogens and possibly genetic factors being superimposed upon the basic iodine deficiency. The iodine supply is now adequate and there is no more goitre in neonates and no endemic goitre in school children in whom the prevalence is usually below 1%. Concomitantly, the nosology of hyperthyroidism has changed. Whereas more than 80% of hyperthyroid patients in the 1950s had nodular goitre the main type of hyperthyroidism today is Graves' disease proper with a small or normal-sized thyroid gland without nodules obviously due to disappearance of the endemic nodular goitre.

Effects of iodide and thyroxine on iodine-deficient mouse thyroid: a morphological and functional study.

Abstract: The effects of iodide and thyroxine (T4) on female mice fed a low iodine diet (LID) for 8 weeks were analysed by morphological, stereological and biochemical methods. Iodide was given at a dose of 10 micrograms/day (HID) or 1 microgram/day (MID), either alone or together with daily injections of 1 microgram T4 for 8 or 40 days. With HID, the thyroid weight and the numbers of follicles and cells remained higher than in controls, although cell necrosis occurred. Colloid volume increased and iodine was stored within the gland: a colloid goitre with non-functioning follicles was produced. With MID, the glands resumed an almost normal appearance. With T4 and LID, progressive normalization occurred, but after 40 days thyroid weight and numbers of follicles and cells remained higher than in controls. Glandular iodine content slowly increased and reached control value. The proportions of 125I-labelled tri-iodothyronine (T3) and T4 in thyroglobulin were reduced. With T4 and HID, the glands resumed a normal appearance. Neither necrosis nor folliculoneogenesis was noted. The proportions of 125I-labelled T3 and T4 in thyroglobulin were reduced, but T3 and T4 serum levels were higher than with HID. With T4 and MID, a normal state was obtained as early as day 8. After 40 days the gland was morphologically and functionally inactive. In conclusion, the association of T4 and iodide seems to be the best way to obtain a rapid and complete involution of thyroid hyperplasia. The administration of T4 prevents the deleterious effects of an excess of iodine on follicular cells, and causes the gland to enter a slow-functioning state.

Thyroid growth immunoglobulins in large multinodular endemic goiters: effect of iodized oil.

Abstract: Iodized oil (10) was administered to 10 goitrous patients recently emigrated to Sao Paulo (SP) from iodine deficiency areas and to 42 goitrous patients from 2 Brazilian chronic iodine deficiency regions, Loreto and Luziania (L). Thyroid growth-promoting immunoglobulin G (IgG) thyroid-stimulating antibody, serum thyroglobulin (Tg), TSH, arid thyroid hormones were measured before and 1 yr after 10 administration. In all patients there was a remarkable reduction of gland mass associated with a significant decrease (P < 0.01) in both basal serum Tg and peak Tg levels after bovine TSH administration. The mean percent Tg increase after bovine TSH treatment was reduced to 82% above basal levels compared with 224% before IO. Mean serum TSH levels, elevated only in the L group [ 7.3 ±11 (±SD) ¼U/ml] decreased to the normal range after 10 (2.5 ± 2.1 ¼U/ml). Serum T3 and T4 concentrations did not change greatly. Tests for microsomal antibodies were negative before and after 10. IgG concentrates of serum obtained bef...

Thyroid status during pregnancy and post partum in regions of iodine deficiency and endemic goiter.

Abstract: During pregnancy the thyroid is subjected to increased demands which is associated with a tendency to endogenous iodine deficiency. Under the conditions of insufficient iodine supply in the GDR the pathophysiological changes result in: 1. prevalence of goiter in about 60% of pregnant women; 2. enlargement of the extent of neck in more than 50% of all pregnant women examined only returning to the prepregnant status in 25%-40%; 3. prevalence of goiter in newborn with 5%; 12.8% of 1948 stilborn had macroscopically an enlarged thyroid gland, the highest weight being 45 g. More than 53% of the stilborn examined by autopsy had a thyroid weight of over 3 g; 4. in contrast to the regions with sufficient iodine supply renal iodine excretion was steadily decreasing during pregnancy and post partum, changing the iodine deficiency from grade II to grade III; 5. low iodine excretion in newborn: 1.3 +/- 0.2 microgram I/day in goitrous (1.2 +/- 0.2 nmol I/mmol creatinine) 2.2 +/- 0.4 micrograms I/day in non-goitrous (2.0 +/- 0.4 nmol I/mmol creatinine); 6. according to ETR more than 50% of the pregnant examined showed a hypothyroid tendency. The pathophysiological changes during pregnancy caused by insufficient iodine supply can be met efficiently by careful thyroid hormone treatment or by the administration of 150 micrograms I daily. A mandatory iodine salt prophylaxis is demanded.

Colorimetric determination of total iodine in foods by iodide-catalyzed reduction of Ce+4

Abstract: An earlier acid digestion determination of iodine in foods was modified to provide an improved detection limit and to allow for the analysis of a greater variety and larger amounts of foods. The organic material in the sample was oxidized overnight by concentrated nitric acid, followed by digestion in a mixture of concentrated sulfuric and 70% perchloric acid. The iodine was determined by an automated colorimetric method based on the iodide-catalyzed reduction of Ce+4 by As+3. The method had an average relative standard deviation of 3.1% for the samples analyzed, and a detection limit of 0.1 ng/mL in the digested solution and 5 ng/g in a 2 g sample prior to digestion. The recovery of added iodine ranged from 90.3 to 101.3%, using external standards. Samples analyzed included NBS Standard Reference Material 1549, and composites of a variety of dairy products, meat, eggs and fish, cereals, and potatoes. The iodine detected in these samples ranged from 9 ng/g for the potato group to 3360 ng/g for the standard reference material.

Measurement of Iodide in Urine Using the Iodide -selective Ion Electrode

Abstract: A simple and rapid way to measure the concentration of iodide in urine with an iodide-selective ion electrode was described. Potentiometric equilibrium was attained in less than 5 min, and a linear calibration curve was obtained over the potassium iodide (KI) concentration range of 10(-2) to 10(-6) M. The coefficients of variation ranged from 6.2 to 10.0% within assay, and 5.4 to 14.4% between assays. The serial dilution of 3 urine samples with different concentration of iodide showed good linear correlations passing through zero. In practice, the chloride ions in urine did not cause serious errors in the measurement of iodide at molar ratios of chloride ion to iodide up to 2 X 10(4). A good linear correlation was obtained between iodide concentrations in urine determined by the electrode method and by the conventional chemical method (r = 0.92). A linear correlation was also observed between the iodide concentrations of 24 h collected urine and those of single morning urine (r = 0.91). The normal iodide content in single morning urine specimens from 127 Japanese people was 5.3 to 62.0 X 10(-6) moles/g creatinine.

Iodine in contrast agents and skin disinfectants is the major cause of hypothyroidism in premature infants during intensive care

Abstract: Unexpectedly, the administration of only 1 ml radiopaque dye and a single skin disinfection with PVP-iodine (PVP-I) induced clinical hypothyroidism in a premature newborn. Therefore, we studied the impact of two different, non-ionic, iodine containing contrast agents (administered for diagnostic reasons), Amipaque 01) and Omnipaque (2), and of PVP-I alone (3) on the immature thyroid gland by measuring TSH, T4, T3 and I excretion before, 5 and 14 days (TSH 0, 5, 14, resp.) after I-exposure. Rarely infants of group 1 and 2 received single doses of PVP-I. The content of free iodide is higher in the solubilized contrast agent (Omni-paque). TSH values(μU/ml) are shown below (medians):

[37] Radioiodination of human alpha interferons by the chloramine T method

Abstract: Publisher Summary This chapter discusses the radioiodination of human alpha interferons by the chloramines T method. The chloramine T method has long been used for incorporating iodine into the tyrosine residues of proteins. The reactants generated are strong oxidants, and for sensitive proteins gentler methods may be needed. The chloramine T reaction involves a slow hydrolysis to generate hypochlorite followed by fast reactions with iodide to form oxidized species that substitute rapidly at positions ortho to the tyrosine hydroxyl, the first substitution facilitating the second. The iodine atom has dimensions similar to those of the phenolate ion, so substitution would likely lead to local distortions in protein structure. The method was originally devised to keep hypochlorite and molecular iodine concentrations as low as possible during the reaction, thus reducing damage and the escape of volatile iodine. In a properly screened and ventilated hood, the reaction poses no great hazard, but particular care is needed to avoid contamination because, in the method described, iodide is allowed to oxidize before it is allowed to react.

Thyroid autoregulation: effect of iodine on glucose transport in cultured thyroid cells.

Abstract: The nonmetabolizable glucose analogs, [3H]2-deoxy-D-glucose and [3H]O-methyl-D-glucose, were used to determine whether iodide influences glucose transport in porcine cells in primary culture. Incubation with iodide (3 h) decreased basal glucose transport with a half-maximum at NaI 3 X 10(-5) M and maximum at 10(-4) M. Iodide (10(-6) M to 10(-4) M) also abolished the stimulatory effect of TSH (1 mU/ml) on glucose transport. The iodide effect on [3H]2-deoxy-D-glucose transport had the following characteristics: 1) it was abolished 24 h after incubation in iodide-free medium; 2) it was prevented by methimazole (3 mM), and correlated with newly formed organic iodine, 3) and it affected the maximum velocity (Vmax) of glucose transport, reducing it from 25.1 to 14.4 and 12.0 nmol/(min mg protein) at 10(-5) M and 10(-4) M NaI, without affecting the Michaelis-Menten constant (Km) (6mM). Iodide-treated cells had a reduced specific binding of [3H]cytochalasin B (38% and 47% with respect to control cells at 10(-5) M and 10(-4) M NaI). These data suggest that iodide treatment reduces the functional carriers mediating glucose transport in the thyroid.

Electrical conductivity of iodine adducts of nylon 6 and other non-conjugated polymers

Abstract: Iodine-nylon 6 adducts containing 70 to 90wt% iodine have been prepared by heating iodine and nylon 6 at 115 and 145° C The electrical conductivity (σ) of the adduct increases with increase in the iodine content and the iodine-nylon 6 adduct containing 90wt% iodine and prepared at 145° C gives σ = 10−3 S cm−1 at 25° C Infrared, nuclear magnetic resonance (1H and13C{1 H}), and powder X-ray diffraction analysis of the adduct show a profound change of the structure around the amide group of nylon 6 and suggest the formation of a-C=NH+-group in the reaction of nylon 6 with iodine The temperature dependences of σ of the idoinenylon 6 adducts prepared at 115° C give activation energies of 51 to 92 kJ mol−1 depending on the iodine content Addition of carbon powder to the iodine-nylon 6 adduct causes an increase in electrical conductivity Other polymers (aliphatic and aromatic nylons, poly(vinyl alcohol), poly (tetrahydrofuran), poly(N-vinylpyrrolidone), poly (4-vi nylpyridine), and poly(acrylonitrile)) which have lone pair or π-electrons also form iodine adducts containing 70 to 95 wt % iodine and the adducts show an electrical conductivity in the range of 10−5 to 10−2 S cm−1 Among the iodine adducts, those of poly(vinyl alcohol) and poly (tetra hydrofuran) show electrical conductivities as high as 15 X 10−2 S cm−1 when the adducts contain about 90 wt% iodine

Development of thyroid function between VI-IX month of fetal life in humans

Abstract: Well-preserved thyroid glands from 28 fetuses 22–34 weeks of gestational age and from 4 term newborns who survived at most 12 days were examined to study thyroid development in late intrauterine life. Total iodine thyroglobulin (Tg), T4, T3 and rT3 were assayed before and after hydrolysis with pronase. In the same maternity unit the cord-serum of 25 healthy term newborns was also assayed and the urine iodine on the day of delivery was tested in 52 newborns and their mothers. Results are expressed as mean values ± SD. The thyroid gland weight ratio to body weight for the preterms was 0.063 ± 0.024; thyroid Tg content 5.9 ± 4.0 mg/g; total thyroid iodine 41.7 ± 35.1 μg/g; Tg iodination 0.72 ± 0.37%; hormone quota of Tg iodine 39.9 ± 12.4. Molar ratios were: T4/Tg 3.3 ± 1.6, T3/Tg 0.25 ± 0.14, rT3/Tg 0.072 ± 0.059. Considerable differences in thyroid iodine content and Tg iodination were observed although the availability of iodine was presumably the same. The high Tg iodination reflects the enhanced uptake of the fetal thyroid. The quantity of iodine involved in hormonogenesis varied greatly among fetuses of the same gestational age, this being in the third term as active as in fully mature thyroids. Hormonogenesis seemed preferentially directed to production of T4 and rT3, which, in the latter case, is higher peripherically. Four preterms with a particularly low level of hormonogenesis were not seen to have deficient levels of thyroid iodine or Tg iodination and the most compromised step was the iodine utilization in the production of hormones. Altogether in the preterms the Tg and thyroid iodine concentrations are about one tenth of the mean values for adults. This might explain the increased risk preterms have of developing transient hypothyroidism, particularly in iodine poor areas or if diseases adversely affect hormonogenesis.

Iodized oil treatment for endemic goiter does not induce the surge of positive serum concentrations of anti-thyroglobulin or anti-microsomal autoantibodies

Abstract: Forty-three goitrous patients (grade II and III, WHO classification), living in areas of chronic iodine deficiency, were treated with an injection of iodized oil (470 mg iodine). Serial measurements of serum thyroid hormone levels after the therapy revealed increasing concentrations of both hormones, with a significantly lower serum T3/T4 ratio, and progressively significantly lower serum TSH mean values. Serum Tg mean value, initially elevated (58 ± 9 ng/ml), decreased after 6 months and returned to the normal range at 36 months of therapy. In none of the examined patients (except for one subject with positive autoantibodies before therapy), it was observed the surge of positive anti- thyroglobulin or anti-microsomal autoantibodies after the iodized oil. We conclude that iodized oil therapy does not induce an abnormal autoimmune reaction in endemic goiter patients.

Evidence, by in Vitro Enzymatic Iodination of Thyroglobulin, that the Efficiency of Coupling Is Determined by the Initial Iodide Concentration*

Abstract: The rate of iodination and the extent and the efficiency of coupling, assessed by the T4 residues formed per atom of iodine bound, have been studied by in vitro enzymatic iodination of iodine-poor (0.01% I) human goiter thyroglobulin (Tgb; 1 μM) with varying concentrations of iodide (0.75 x 10−8− 10−4 M I−), lactoperoxidase (0.1−5 μg/ml), and hydrogen peroxide (H2O2) generated from glucose (1 mg/ml) and glucose oxidase (0.025—2.5 mU/ml). Under the experimental conditions used, variations in the H2O2 concentration affect the rate of iodination, but not the extent of coupling. Variations in the peroxidase concentration do not affect the rate of iodination or the coupling efficiency. Variations in the iodide concentration do not affect the rate of iodination, but do affect the coupling efficiency, which is higher the lower the initial iodide concentration. Both iodination and coupling take place almost simultaneously. They are catalyzed by peroxidase, and iodination is completed earlier the lower the iodide ...