Showing papers on "Iodine published in 1997"

Potassium Iodide as a Chemical Actinometer for 254 nm Radiation: Use of Iodate as an Electron Scavenger

Abstract: — A solution of 0.6 M iodide and 0.1 M iodate in 0.01 M borate buffer (pH 9.25) can be used as a chemical actinometer to measure the incident fluence from a low-pressure mercury lamp that puts out more than 85% of its energy at 254 nm. The actinometric solution is optically opaque to light below 290 nm and is optically transparent to wavelengths greater than 330 nm. Hence, the solution absorbs all of the germicidal wavelengths but little if any of the ambient light normally present in the laboratory. Iodate acts as an electron scavenger and prevents the back reaction of the free electron with the iodine atom following UV excitation of KI. Irradiation results in the linear formation of triiodide, which is quantitated by measuring its absorbance at 352 nm. The quantum yield for this system is approximately 0.75 0.03 at 20.7AoC or approximately three times greater than that obtained previously using nitrous oxide as an electron scavenger. A model is proposed to account for this difference. A precise expression to account for the concentration and temperature dependence of the quantum yield is given by pH = 0.75(1 + 0.23[C - 0.577])(1 + 0.02[T - 20.7]) where C is the concentration of iodide and T is the temperature. The concentration of iodide can be obtained from the absorbance at 300 nm prior to irradiation using 1.061 MJ cm−1 as the molar extinction coefficient. This actinometric system meets the quality criteria established by the International Union of Pure and Applied Chemistry with the caveat that it is designed to measure only germicidal radiation (i.e. wavelengths less than 290 nm).

Effect of iodized salt on thyroid volume of children living in an area previously characterized by moderate iodine deficiency.

Abstract: It is well established that an adequate iodine intake prevents iodine deficiency disorders. Prophylaxis through iodized salt is able to correct urinary iodine deficiency and to prevent goiter endemia, but scanty data are available about its effect on decreasing the thyroid size in goitrous children born before prophylaxis. The prevalence of goiter was evaluated by ultrasound in the school-children population of an area of Eastern Tuscany (Tiberina Valley) characterized by moderate iodine deficiency in 1985. At present, after the implementation of voluntary iodized salt consumption, iodine urinary excretion was borderline sufficient (median, 98 micrograms/L). Goiter prevalence was higher at ultrasound (17%) than by palpation (10%). The median thyroid volume ranged from 3.1 mL in 7-yr-old children to 9.2 mL in 14-yr-old children. In the 7-10 yr age class (i.e. in children born after iodine prophylaxis), no statistical difference in thyroid volume was found with respect to controls. In older children (11-14 yr) born before the institution of iodine prophylaxis, the median thyroid volume was significantly higher than that in age-matched controls. Moreover, in this cluster of subjects, the median thyroid volume in nongoitrous children was higher than that in controls. In conclusion, the data of the present study indicate that the iodized salt prophylaxis is able to prevent the development of goiter in children born after the implementation of iodized salt consumption and to further control thyroid enlargement in older children, but is less effective (or rapid) in reducing goiter size in children exposed to iodine deficiency in the first years of life.

Urinary iodine excretion during normal pregnancy in healthy women living in the southwest of France: correlation with maternal thyroid parameters.

Abstract: A prospective study was undertaken to evaluate urinary iodine excretion and changes of maternal thyroid function during pregnancy in healthy women living in the southwest of France. The cohort included a total of 347 pregnant women (mean age 28.0+/-0.5 years). Iodine concentration in a random urine sample and thyroid tests (free thyroxine [FT4], free triiodothyronine [FT3], thyrotropin (TSH), thyroxine-binding globulin [TBG], and thyroglobulin [Tg]) were measured at initial presentation (before 12 weeks of gestation), and during the ninth month of pregnancy. A thyroid ultrasound was performed 1 to 5 days after delivery in 246 mothers. Mean urinary iodine levels were low during the first trimester (6.9+/-0.4 microg/dL), as well as during the ninth month of pregnancy (8.6+/-0.6 microg/dL). During pregnancy, FT4 and T3 concentrations decreased (p < .001), and TSH and Tg concentrations increased (p < .001). Thyroid hypertrophy (thyroid volume greater than 18 mL) was present in 15.4% of women whose first trimester urinary iodine concentration was less than 5 microg/dL, but was present in only 3.5% of women whose urinary iodine concentration was greater than 10 microg/dL. A goiter (thyroid volume greater than 22 mL) was present in 11% of the mothers. In conclusion, this prospective study shows that urinary iodine excretion is low in pregnant women living in the southwest of France. This low iodine intake is associated with reduced circulating thyroid hormone levels and growth of the thyroid gland. These data point to the need of an increased iodine supply in these pregnant women to reduce the potential consequences of low iodine intake on maternal thyroid economy.

Determination of Iodine in Food-related Certified Reference Materials Using Wet Ashing and Detection by Inductively Coupled Plasma Mass Spectrometry

Abstract: Iodine was accurately determined in food-related certified reference materials (CRMs) by wet ashing in closed steel bombs using a mixture of nitric acid and perchloric acid followed by measurement of iodine by ICP–MS at m/z 127. The iodine concentrations determined were 0.15–4.59 mg g −1 (dry mass). Potentially volatile iodine species such as hydrogen iodide were converted during the ashing procedure to nonvolatile species. Hereby memory problems in the ICP–MS due to volatile iodine were prevented. The concentric nebulizer which was used in combination with a low dead-volume cyclonic spray chamber improved the iodine signal intensity and reduced the wash-out time between samples compared with the standard Ryton double-pass spray chamber equipped with a cross flow nebulizer. Iodine contamination from the PTFE liners of the bombs led to blank values at an average of 9 ng per ashing. The limit of detection which was based on three standard deviations of the blank was 30 ng g −1 (dry mass). By adding 3% v/v methanol to the analyte solutions and increasing the plasma power to 1200 W, the signal-tonoise ratio and hence the limit of detection was improved by 50% due to the signal enhancement effect by carbon of the incompletely ionized iodine.

Distribution of methyl iodide, ethyl iodide, bromoform, and dibromomethane over the ocean (east and southeast Asian seas and the western Pacific)

Abstract: Ambient concentrations of four marine-derived halocarbons (methyl iodide, ethyl iodide, bromoform and dibromomethane) and two man-made halocarbons (trichloroethylene and tetrachloroethylene) were measured during western Pacific cruises and east and southeast Asian cruises. Ethyl iodide was detected in the atmosphere for the first time and was identified as an atmospheric iodine source compound. Bromoform concentrations were positively correlated with those of dibromomethane, and methyl iodide showed variations similar to those of ethyl iodide. However, there was no correlation between the bromocarbons and the iodocarbons. The concentrations of methyl iodide and ethyl iodide changed more markedly, possibly owing to higher rates of photodecomposition of iodocarbons.

Iodine status of New Zealand residents as assessed by urinary iodide excretion and thyroid hormones

Abstract: The aims of this study were (1) to compare various measures of I status, and (2) to assess urinary I and thyroid hormone status of residents of two areas of New Zealand where, before the iodization of salt, goitre was endemic due to low soil I. A total of 189 subjects (102 males, eighty-seven females) were recruited from the Dunedin Blood Transfusion Centre, and 144 (sixty-seven males, seventy-seven females) from the Waikato Blood Transfusion Centre between November 1993 and June 1994. Blood was taken for thyroid hormone assays, and subjects collected a fasting overnight urine specimen, a double-voided fasting urine sample, and a complete 24 h specimen for iodide and creatinine analyses. Positive correlations (P < 0.0001) between daily iodide excretion and iodide concentrations in fasting and double-voided fasting urines, identical median values for iodide concentrations in the three samples, and similar numbers of subjects classified as at risk from I deficiency disorders according to the International Committee for the Control of Iodine Deficiency Disorders/World Health Organization categories (World Health Organization, 1994) confirmed indications from earlier studies that fasting urine samples were suitable for population studies. However 24 h urinary iodide excretion remains the recommended measure for individual I status. Waikato residents excreted more iodide in urine and all measures were significantly greater than for Otago residents. However median urinary iodide excretions for both areas (60 and 76 microgram/d for Otago and Waikato respectively) were considerably lower than those reported previously for New Zealand. Thyroid hormone concentrations were within normal ranges. Our findings suggest that I status of New Zealanders may no longer be considered adequate and may once again be approaching levels of intake associated with clinical I deficiency.

Dietary Iodine and Selenium Interact To Affect Thyroid Hormone Metabolism of Rats

Abstract: The interaction of dietary selenium and iodine on the activities of the selenoenzymes, selenium-dependent glutathione peroxidase (GSH-Px), and type I deiodinase (DI-I), and the thyroid hormones thyroxine (T4) and triiodothyronine (T3) were studied. Male weanling Sprague-Dawley rats were fed an AIN-93G diet for 6 wk with modified selenium and iodine concentration as follows: three levels each of iodine and selenium (0.03, 0.2 added and 1.0 added mg iodine/kg diet, and 0.05, 0.18 added and 1.0 added mg selenium/kg diet) were used in a 3 x 3 factorial design. Renal, but not hepatic, DI-I activity was lower in rats with low selenium intake than in controls. Circulating T3 concentration was not affected by the dietary levels of iodine or selenium. Unlike in liver, kidney and erythrocytes, thyroidal GSH-Px activity was not lower than in controls in rats with low selenium intake, but was significantly higher when iodine intake was low. Significant interactions of iodine and selenium on serum T4 and thyroidal GSH-Px activity were observed. Serum T4 was maintained at control levels when both dietary iodine and selenium were low, but not when iodine alone, or selenium alone, was low. Activity of thyroidal GSH-Px was lowest in rats fed a diet containing high iodine and low selenium. The results suggest that high iodine intake, when selenium is deficient, may permit thyroid tissue damage as a result of low thyroidal GSH-Px activity during thyroid stimulation. A moderately low selenium intake normalized circulating T4 concentration in the presence of iodine deficiency.

Sub-surface iodide maxima: evidence for biologically catalyzed redox cycling in Arabian Sea OMZ during the SW intermonsoon

Abstract: Sub-surface I− maxima (200–600 nM) were found in five of the six profiles from the Somali and Arabian basins of the Northwest Indian Ocean. In addition to these maxima, dissolved I− exhibited normally high (100 nM or greater) values in the surface and values ranging from 3 to 40 nM at depth, which are higher than other open oceanic systems. Sulfide was generally found to be less than 2 nM in the water column, indicating that the chemical reduction of iodate by sulfide is not important in regulating iodine speciation in the Northwest Indian Ocean. These novel high iodide values below the euphotic zone do not appear to be related to other bulk chemical or hydrographic features (σθ) but may be the result of two distinct biologically mediated remineralization processes: (1) the direct reduction of I03− to I− as seen in the sub-surface maxima, and (2) release of I− from CI bonds during the decomposition of organic matter. Iodine normalized to salinity, specific iodine, is not found to be conservative in this system. Overall, our specific iodine data support the incorporation of iodine into organic material in the surface. Iodide, when present below the euphotic zone, is a product of the decomposition of that exported organic material. These data and processes are consistent with those found previously in the Black Sea and the Chesapeake Bay. However, in the Northwest Arabian Sea, iodide and oxygen are measurable throughout the water column, indicating that the system is not at equilibrium with the prevailing redox condition and that traditional thermodynamic considerations of pE do not appear to be applicable. Porewater iodide in the top 150 cm increased with depth to approximately 19 μM as a result of the release of I− during decomposition of organic matter.

Salt Effects of Lithium Chloride, Sodium Bromide, or Potassium Iodide on Liquid−Liquid Equilibrium in the System Water + 1-Butanol

Abstract: Liquid−liquid equilibrium data for the partially miscible systems of water + 1-butanol + salt were measured at 25 °C. The salts used were lithium chloride, sodium bromide, and potassium iodide. The systems were compared in terms of salting-out efficiency and solvation effects.

Rapeseed Meals, Methimazole, Thiocyanate and Iodine Affect Growth and Thyroid. Investigations into Glucosinolate Tolerance in the Pig

Abstract: In two factorial experiments with a total of 81 growing pigs, the effects of antithyroid compounds and rapeseed meal (RSM) diets differing in glucosino-late content were tested without or with supplementary iodine. In Experiment 1, a 4×3 factorial arrangement was used to investigate the effects of antithyroid compound inclusion and supplementary iodine. Pigs received a grain–soya bean meal diet (control) or this diet with 250 mg kg-1 methimazole (MMI), 1000 mg kg-1 thiocyanate (SCN- as KSCN) or 80 g kg-1 high glucosinolate RSM (9·5 mmol glucosinolates kg-1), each diet supplemented without or with iodine; 0, 125 μg kg-1 (requirement) or 500 μg kg-1. In Experiment 2, a 5×3 factorial arrangement was used to study the effects of dietary glucosinolate content and iodine supplementation. Pigs received a grain–soya bean meal diet or four diets with 160 g kg-1 RSM differing in glucosinolate content (0·6, 2·4, 6 or 19 mmol kg-1 diet), each diet supplemented with iodine: 62·5 μg kg-1, 125 μg kg-1 (requirement) or 250 μg kg-1. Irrespective of the iodine dosage, MMI suppressed production of thyroxine and resulted in goitre, myxoedema and cretinism. SCN- induced clinical hypothyroidism when there was no supple-mental iodine. Despite high iodine supplementation, glucosinolate load (19 mmol kg-1 diet) decreased growth, feed intake, iodine store of the thyroid and serum concentration of thyroid hormone and resulted in goitre formation. In the case of diets with ⩽6 mmol glucosinolates kg-1, iodine prevented antithyroid effects. However, more iodine was required by these pigs than by control animals to a high T4 serum concentration. The lowest glucosinolate level tested (0·6 mmol kg-1 diet) yielded the same thyroid hormone status and thyroid weight as the control, however, the iodine content of thyroid gland was decreased. In conclusion, iodine administration prevents the effects of a low glucosinolate intake only, by overcoming the depressed thyroxine released of the thyroid, resulting in regression of goitre. © 1997 SCI.

Investigation of the IC-ICP-MS determination of iodine species with reference to sample digestion procedures

Abstract: The determination of iodine in aqueous solutions suffers from several serious problems, caused by the formation of iodine species, derived from the oxidative pretreatment of biological materials. For the determination of these iodine species an ion chromatograph was coupled with an ICP-mass spectrometer. Because of the possible interconversion of the iodine species depending on the pH-value, different eluent-column combinations were used for acidic or alkaline sample solutions, respectively. Iodide, iodate, and several not identified, presumably organo-iodine species could be separated and detected. Unfortunately, the iodine (I2) itself could not be determined with the method proposed. The reaction products of pretreatment are influenced strongly by the matrix. Mixtures of different iodine containing components are received, dependent on the matrix composition and particularly on the pH-value.

Thyrotropin and thyroglobulin as an index of optimal iodine intake: correlation with iodine excretion of 39,913 euthyroid patients.

Abstract: The recommendations for the dietary allowance of iodine are 150 micrograms per day for adolescents and adults. Thyrotropin (TSH) and thyroglobulin (Tg) can be used as surveillance indicators for assessing iodine deficiency disorders. We compared the relation between TSH and Tg, free triiodothyronine, and thyroxine serum levels with urinary iodine excretion in 2311 untreated euthyroid patients using our modified cericarsenite method. An adequate iodine intake may be assumed when TSH and Tg values are at the lower end of the normal range. Patients were grouped according to urinary iodine excretion and goiter size. In the group with an iodine excretion between 201 and 300 micrograms of iodine per gram of creatinine, the lowest TSH values and even low Tg levels could be shown. We conclude that an iodine intake of approximately 250 micrograms/day is associated with the lowest TSH stimulation to thyrocytes. In the groups separated according to thyroid size, significantly higher Tg levels were found in the patients with uninodular and multinodular goiter as a result of longstanding iodine deficiency, whereas actual urinary iodine excretion did not differ significantly. Additionally, iodine excretion of 39,913 euthyroid patients between 1984 was 1996 was examined. In Austria iodized salt (10 mg KI/kg) was introduced by law in 1963 and increased to 20 mg KI/kg salt in 1990. An initial increase of iodine excretion until 1993 was followed by a decrease in 1994 and 1995 without further changes in 1996. These results show that iodine intake has improved since 1984; however, in 1996 iodine excretion in one-third of the investigated patients was under 100 micrograms per gram of creatinine and more than 80% had less than 200 micrograms per gram of creatinine.

Effects of selenium and iodine deficiency on thyroid hormone concentrations in the central nervous system of the rat.

Abstract: Objective: The effects of single and combined nutritional selenium and iodine deficiency on intracellular thyroid hormone concentrations and type II 5'-iodothyronine deiodinase (5'D-II) activity were examined in different regions of the adult rat brain. Design: Four groups (n=6) of weanling female Wistar rats proceeding from a breeding line fed a selenium-deficient or a selenium-replete diet for 3 generations, were fed selenium-deficient, iodine-deficient, combined selenium- and iodine-deficient or selenium- and iodine-replete diets for 2 months before they were killed. Methods: Tissue thyroxine (T 4 ) and tri-iodothyronine (T 3 ) concentrations were determined by highly sensitive RIAs after extraction of the iodothyronines from the tissue samples. The measurement of 5'D-II was based on the release of radioiodide from the 125 I-labelled substrate. Results: Selenium deficiency significantly decreased tissue T 3 concentrations in the hippocampus, hypothalamus and striatum to 70-80% of controls, whereas no significant changes were found in the cerebellum, cerebral cortex and brain stem. Tissue T 4 concentrations were only marginally affected with the exception of a 35%, increase in the cerebral cortex. Iodine deficiency dramatically diminished serum T 4 levels as well as intracellular T 4 concentrations in all regions examined up to 10-30% of control. In spite of a threefold enhancement of 5'D-II,the iodine-deficient animals still had a significant reduction of tissue T 3 concentrations (50-65% of controls) in all regions excepting the cerebellum. The combination of selenium and iodine deficiency did not significantly alter this pattern of changes. Conclusions: These findings suggest that prolonged selenium deficiency as well as iodine deficiency may compromise thyroid hormone homeostasis in the adult brain leading to tissue hypothyroidism and therefore to impaired brain function.

Regeneration of Inorganic Iodine Species in Loch Etive, a Natural Leaky Incubator

Abstract: Iodine species concentrations and oxygen concentrations were measured in the isolated bottom waters of a Scottish fjord during two separate periods of isolation, each lasting about a year. The rates of biogeochemical change of the species were estimated by allowing for diffusive fluxes from the bottom water. This shows that iodide concentration increased during the two isolations which occurred in the study period, but that a sustained loss of iodate in the first isolation was followed by a gain during the second. Combined, these changes led to a small and gradual increase in total iodine concentration in both isolations. The iodide production is ascribed to regeneration of material with an I:C ratio of the order of 10−5in the sediment. The iodide oxidation rate is small but significant at about 0·03±0·01 μM year−1.

Iodine intake and urinary excretion among adults in the Netherlands.

Abstract: OBJECTIVE To assess the prevalence of low and marginal iodine intake and urinary iodine excretion among adults in the Netherlands and to investigate determinants of urinary iodine excretion. DESIGN AND SUBJECTS The study population consisted of 444 people aged 20-79 y, balanced for sex and 10 y age classes with an over-representation of people with a low habitual intake of vitamin B6. Food consumption was measured by three day food records and 24 h urine was sampled twice. RESULTS AND CONCLUSIONS On average, iodine intake (mean of three days) in men was in the recommended range of 150-300 microg/d, but average intake in women was not. Mean 24 h urinary excretion values confirmed this observation. Estimation of the prevalence of low iodine excretion depended on the parameter chosen (absolute per 24 h, per kg body weight per 24 h, as concentration or per creatinin). The prevalence of low iodine supply, based on intake <100 microg/d (mean of three days) and intake or excretion parameters per creatinin excretion or per kg body weight, varied from 4-14% among adult women and from 5-17% among adult men. The prevalence of marginal iodine intake (<50 microg/d) and excretion was less than 5% in all adult age-sex groups. Urinary iodine excretion was most strongly associated with intake of iodine as such or as bread in combination with urinary excretion of sodium or potassium, confirming the importance of iodized salt (in bread) for iodine status. Age and total energy intake had a relatively minor impact on urinary iodine excretion.

Determination of iodine in milk and oyster tissue samples using combustion and peroxydisulfate oxidation.

Abstract: Two methods are described for the preparation of samples for total iodine measurement in biological matrices. In the first method, the samples were combusted in a stream of oxygen to release iodine that, subsequently, was trapped in a solution as iodide. The second method is a new approach in which the samples were oxidized in a basic solution of peroxydisulfate. In this case, the iodine was retained in solution as iodate. Total iodine was measured by gas chromatographic analysis of the 2-iodopentan-3-one derivative. The methods were tested using Standard Reference Materials (SRMs) 1549 Non-Fat Milk Powder, and 1566a and 1566 Oyster Tissue. Also, KI and KIO 3 were used for testing the procedures. The results obtained for the SRMs, given as average ± standard deviation in µg g - 1 , were: 3.39 ± 0.14 and 3.40 ± 0.23 for SRM 1549; 4.60 ± 0.42 and 4.51 ± 0.45 for SRM 1566a; and 2.84 ± 0.16 and 2.76 ± 0.06 for SRM 1566; values corresponding to combustion and wet oxidation, respectively. Overall, the absolute recoveries varied between 91 and 103%. These methods can also be used in the preparation of targets for the measurement of 129 I using accelerator mass spectrometry.

Experimental reproduction of iodine deficiency in cattle

Abstract: The role of iodine deficiency in stillbirth/perinatal weak calf syndrome was investigated in pregnant heifers. Five heifers were fed an iodine deficient diet (mean [sd] iodine concentration 0.06 [0.01] mg/kg dry matter [DM]) and six received an iodine sufficient diet (mean [sd] iodine concentration 1.45 [0.27] mg/kg DM). The diets consisted of wheat and soyabean meal with added minerals and vitamins (with or without iodine) and were fed to the heifers over the final four to five months of pregnancy. The iodine deficient diet produced clinicopathological changes and pathological changes in the thyroid glands of both the heifers and their offspring. However, all the calves in the iodine deficient group were born clinically normal.

Control of iodine deficiency using iodination of water in a goitre endemic area.

Abstract: Salt iodination is the method of choice for prevention of iodine deficiency in most parts of the world. However, establishment of such a program frequently involves considerable changes in the marketing and distribution patterns and requires years to achieve. This study was conducted to evaluate the efficiency of using well-defined water sources containing iodine-saturated silicon matrices for providing adequate iodine supply to an iodine deficient population in Kordofan State, Western Sudan. A system of water iodination using silicon matrices containing 30% sodium iodide placed in polyethylene baskets was used in four villages using either traditional wells or hand pumps. Before and every 6 months after iodination of water, urine and blood samples were obtained for determination of iodine and thyroid-related hormones, respectively. Goitre assessment on the village populations were performed at the start and 2 years later. Improvements in iodine status were recorded in all the study villages. The water iodine concentrations increased and a higher iodine content was observed in the hand pumps compared to the traditional wells. The median urinary iodine concentrations increased significantly, from 0.19, 0.20, 0.19, 0.11 to 1.20, 1.10, 0.37, 0.30 mumol/l in the four villages, respectively. The percentages of subjects with serum TSH above 4 mU/l were decreased from more than 30% before iodination to less than 15% at 2 years after iodine supply and the mean serum thyroxine hormone values rose. The rates of goitre decreased from 69% to less than 25%. The study shows that this system is effective, cheap, safe and practically applicable under conditions prevailing in rural areas in developing countries with iodine deficiency.

Synthesis of homoallylic (but-3-enylic) alcohols from aldehydes with allylic chlorides, tin( II ) chloride and potassium iodide in water

Abstract: Homoallylic (but-3-enylic) alcohols have been prepared in good yields by reductive allylation of aldehydes in water with various allylic chlorides in the presence of tin(II) chloride and potassium iodide. The Barbier type reaction with prop-2-ynyl chloride is also achieved under the same conditions.

Thiamacrocyclic chemistry: Synthesis of a novel oxadithiacrown and its copper iodide complex

Abstract: A mixed oxa–thia macrocycle incorporating a rigid ‘horseshoe-shaped’ aromatic moiety, 1,11,21-trioxa-8,14-dithia[2,9,2]paracyclophane, L, has been synthesised. The molecular structures of L and of its copper iodide complex have been determined by single-crystal X-ray diffraction methods. There are two independent conformations observed in the solid state for the macrocycle, L. Its copper iodide complex [Cu 2 I 2 (L)]·1.25MeCN, crystallises, in a 2∶1 metal∶crown ratio, as a one-dimensional infinite array of cubane-like units consisting of four copper atoms, four iodine atoms and four sulfur atoms from four different macrocycles.

Effects of marginal iodine deficiency during pregnancy: iodide uptake by the maternal and fetal thyroid

Abstract: Iodide uptake by the thyroid is an active process. Iodine deficiency and pregnancy are known to influence thyroid hormone metabolism. The aim of this study was to clarify the effects of iodine deficiency and pregnancy on iodide uptake by the thyroid. Radioiodide was injected intravenously into nonpregnant and 19-day pregnant rats receiving a normal or marginally iodine-deficient diet. The uptake of radioiodide by the thyroid was measured continuously for 4 h. The absolute iodide uptake by the maternal and fetal thyroid glands at 24 h was calculated by means of the urinary specific activity. Pregnancy resulted in a decrease in the absolute thyroidal iodide uptake. Marginal iodine deficiency had no effect on the absolute iodide uptake by the maternal thyroid. The decreased plasma inorganic iodide was compensated by an increase in thyroidal clearance. A similar compensation was not found for the fetus; the uptake of iodide by the fetal thyroid decreased by 50% during marginal iodine deficiency. This can lead to diminished thyroid hormone production, which will have a negative effect on fetal development, especially of the brain.