Thyroid Iodine Content Research Articles

Excess Iodide and Thyroid Function in the Developing Chick Embryo

The effects of adding excess iodide (I -) to egg yolks were studied on the quantity of iodide transferred to the chick embryo and on thyroid function from Days 8 to 18 of incubation. Following injection of either 0.5 or 1 mg of iodide into the yolk on the second day of incubation, embryonic plasma iodine levels increased significantly over levels of controls at the same age. These increases were proportional to the amount of excess iodide in the yolk. Moreover, a constant ratio between the iodine levels of the allantoic fluid and the plasma was maintained for any given day of incubation. Up to Day 10, the iodine content of the embryonic thyroid was closely correlated with the increased plasma iodine concentrations. After Day 10, concomitant with the establishment of the hypothalamo-adenohypophyseal-thyroid axis, the increase in thyroid iodine no longer paralleled that of plasma iodine, but was only twice that of controls. As thyroid weight doubled in these treated embryos, thyroid iodine concentrations of control and treated embryos were similar. Iodide excess did not block thyroid iodine organification, nor was there any modification of iodine distribution among the different iodo-amino acids. Moreover, despite the doubling of thyroid hormone content in the goiters of treated embryos, circulating levels of thyroid hormones in control and treated embryos were not different.

Stillbirth/perinatal weak calf syndrome: preliminary pathological, microbiological and biochemical findings.

Microbiological, biochemical and pathological data collected from 293 calves which were either stillborn, or born alive and either failed to breathe or failed to breathe for more than about 10 minutes are presented. No bacteria were recovered from 96 of the calves (32.7 per cent), and bacteria which were considered significant were isolated from only four (1.4 per cent). Evidence of leptospiral infection was found in 75 calves (25.5 per cent). Of 64 calves examined for bovine virus diarrhoea (BVD) and infectious bovine rhinotracheitis (IBR) antigens, two were positive for BVD virus and none for IBR virus. The mean (+/- sd) liver vitamin E and kidney selenium concentrations, determined in 148 of the calves, were 2.0 +/- 0.76 micrograms/g wet matter and 0.47 +/- 0.17 micrograms/g wet matter, respectively. The thyroid iodine concentration in 15 of 71 calves (21 per cent) was less than 300 micrograms/g wet matter and the mean (+/- sd) thyroid weight of 266 of the calves was 18.5 +/- 11.6 g. Evidence of severe trauma was found in 19 of the calves (6.5 per cent). Histological findings included thyroid epithelial hyperplasia, hepatic haemosiderosis, erythrophagocytosis in the spleen, perivascular haemorrhage in brain and adrenal glands, and accumulation of leucocytes in blood vessels.

Course of thyroid iodine concentration during treatment of endemic goitre with iodine and a combination of iodine and levothyroxine

In the treatment of endemic goitre, the concept of giving levothyroxine in combination with iodine offers a promising therapeutic approach by influencing not only TSH secretion but also intrathyroidal iodine content. However, little is known about the doses of iodine necessary to correct intrathyroidal iodine deficiency. To get more information on this important issue, we conducted a prospective, double-blind study on the effect of a monotherapy with 500 micrograms iodide/day and a combined treatment with 100 micrograms levothyroxine and 100 micrograms iodide/day on thyroid iodine concentration as measured by fluorescence scintigraphy. In a group of 12 patients, a 4-month treatment with 100 micrograms levothyroxine and 100 micrograms iodide/day did not significantly affect thyroid iodine concentration (0.35 +/- 0.14 vs 0.37 +/- 0.11 mg/g). The application of 500 micrograms iodide/day in these patients during a second 4-month period resulted in a sharp increase in thyroid iodine concentration from 0.37 +/- 0.11 to 0.61 +/- 0.14 mg/g (p less than 0.01). Another group of 8 patients first treated with 500 micrograms iodide/day also showed a significant increase in iodine concentration from 0.35 +/- 0.14 to 0.65 +/- 0.20 mg/g (p less than 0.01). After switching to the combination regimen during a second 4-month period, thyroid iodine concentration slightly decreased, particularly in those patients with high iodine concentrations after monotherapy with iodide (0.65 +/- 0.20 vs 0.50 +/- 0.12 mg/g, p less than 0.05). In conclusion, treatment with 500 micrograms iodide/day could sharply increase thyroid iodine concentration in patients with endemic goitre. In contrast, a combination of 100 micrograms levothyroxine and 100 micrograms iodide/day had no significant effect on thyroid iodine concentration.

Long-term effects in skin and thyroid after radiotherapy for skin angiomas: a French retrospective cohort study

To evaluate the long-term effects of skin angioma irradiation, a recall programme was established which included the systematic recalculation of the radiation dose to the skin and the thyroid. 22% of the 6229 patients contacted had a dermatological examination which revealed cutaneous dystrophy in 81% of the 1137 exposed angiomas and in 39% of the 208 unexposed angiomas. The risk of dystrophy (telangiectasia, hypopigmentation, superficial and subcutaneous atrophy) was 12.1 higher ( P < 0.0001) among patients who had received a surface skin dose above 30 Gy than among those who had received a dose of 10 Gy or less. The relative risk for each dystrophy component increased significantly ( P < 0.001) with surface skin dose. Furthermore, 14 basal cell carcinomas (BCC) were observed in 12 patients from the exposed group for all quantities of radiation, with a mean latency period of 22 years. No BCC was observed for a surface skin dose below 10 Gy. Thyroid testing was done on a subgroup of 431 patients whose thyroid gland had been particularly exposed during angioma irradiation. After recalculation, the dose delivered to the gland was below 1 Gy in 98% of patients. Only 13 thyroid nodules were discovered (1 hot and 12 cold). 1 patient with a cold nodule had a malignant thyroid tumour 21 years after irradiation. He belonged to the group of 7 patients who had received a thyroid dose above 1 Gy. Although no morphological abnormality was found in 98% of the tested patients, most (92%) had a thyroid iodine content below 15 mg (the standard French value), while a raised serum thyroglobulin level (> 30 ng/ml) was observed in 17%. This might confer a higher risk of subsequently developing thyroid nodules.

Prüfung von Extraktionsschroten aus Winterrapssaat mit unterschiedlichem Glucosinolatanteil an Schweinen unter Berücksichtigung der Iodversorgung

In the experiment, 2 x 12 growing pigs received 19 or 6.7 mmol glucosinolates + aglucones/kg feed via conventional rapeseed meal (RSM) or RSM of a newly bred variety. These pigs and 24 littermates pair fed with a soya bean meal (SBM) diet were subdivided in groups of 4 animals each. Their diet contained either no supplementary iodine or an iodine supplementation of up to 1 mg/kg feed. In the RSM and SBM groups the lack of additional iodine lowered the serum T4 and T3 content below the detection limit and caused goitre with about 1 mg iodine in the total thyroid. The SBM diet with 0.0625 mg supplementary iodine/kg increased the serum T4 level and reversed the thyroid enlargement but not that of epithelial cells. The hypothyroidism (goitre and serum T4 level approximately 10 nmol/l) still existed in the case of this iodine dosage together with the RSM of the newly bred variety. A serum T4 level comparable to that of the animals fed SBM was only reached by supplementing the low glucosinolate diet with 0.25 mg iodine/kg feed. The iodine content of the thyroid, however, was reduced by 50 per cent. Though thyroid and epithelial cells were enlarged, this enlargement was not so obvious as in animals exposed to higher glucosinolate level. In spite of 1 mg supplementary iodine/kg feed, the feeding of the conventional RSM resulted in a lower serum T4 level a reduced thyroid iodine content and the enlargement of thyroid and that of epithelial cells. Compared to the high glucosinolate RSM, a significantly lower antithyroid effect of the low glucosinolate RSM was found in pigs with iodine supply. The degree of thyroid enlargement and the serum T4 level were the criteria.

Measurement of Thyroid Iodine by CT

For evaluation of thyroidal iodine kinetics and thyroid nodules, we carried out quantitative in vivo measurement of thyroid iodine concentration by CT. Neuron activation analysis of iodine content was conducted on 48 thyroid fragments without calcification operatively obtained from 18 patients who had undergone CT of the thyroid without contrast enhancement. The CT attenuation values were obtained from the regions of interest in the CT image that corresponded to the analyzed fragment. When iodine concentration in the thyroid tissue was greater than 0.02 mg/g, the CT values correlated linearly with the iodine concentrations in thyroid nodules, thyroids with diffuse thyroid disease, and normal thyroids. The relationship is represented by the following formula: iodine concentration (mg/g) = (CT value-65)/104. The relationship between iodine concentration and CT value in diffuse thyroid disease, thyroid nodules, and normal thyroids was not significantly different.

Thyroid function of gerbillidae ( Meriones (M) Libycus, M. shawi shawi and Psammomys (P) Obesus): Field studies in southern Tunisia

1. Thyroid function was studied in three desert rodents P. obesus, M. shawi and M. libycus. Of the three, Psammomys had a diet richer in water, salt and iodine than the others. 2. Despite the difference in iodine supply the thyroid weights, iodine and T4 concentrations and the plasma T 4 levels were not significantly different for the three species. 3. This was because the major part of food iodine in Psammomys was non-assimilable and, was thus excreted in the faeces. 4. Only thyroid and plasma T 3 concentrations and plasma T 3/T 4, ratios were lower in Psammomys than in Meriones as a result of a slight overload of iodine. 5. T 4 production rates were not different between Psammomys and M. shawi and were analogous to those found in rodents of the temperate zone. 6. Thus, these species do not present hypothyroid characteristics, a hypothesis proposed to explain the low metabolic rate of desert rodents.

Thyroid iodine content and serum thyroglobulin level following external irradiation to the neck for Hodgkin’s disease

Fifty-four clinically euthyroid patients were evaluated 1 up to 17 yr after external irradiation to the neck for Hodgkin's disease. T4 level was decreased in 6%, while basal TSH level was increased in 44%, and TSH response to TRH was increased in 66% of the patients with normal basal TSH level. Thyroid iodine content (TIC), measured in 50 patients, was below 5 mg in 18. The 29 patients with normal basal TSH level had a mean TIC (6.8 +/- 2.7 mg) significantly lower (p less than 0.01) than the control population (14.6 +/- 5 mg). A significant positive correlation was found between log T4 and log TIC (r = 0.55, p less than 0.01). Thyroglobulin (Tg) level was increased in 53% of the patients with no palpable thyroid abnormality. It was not related to TSH level but was related to younger age at irradiation. T4 treatment decreased Tg level to the normal range in 5 of 8 patients. These facts suggest subclinical thyroid abnormalities and patients with elevated Tg levels should be considered at risk for developing a thyroid tumor.

Subacute toxicological examination of Dithane M-45

A subacute toxicological study of the effects of the ethylene-bisdithiocarbamate-containing fungicide Dithane M-45 (80% mancozeb) was carried out in male Wistar rats. The rats were given Dithane mixed in the feed at doses of 0, 10, 50, 75, 113, 169, 253 or 379 mg/kg body weight for 12 wk. One-third of the rats given 379 mg Dithane/kg body weight died, and doses of ⩾169 mg/kg decreased the growth of the rats as well as the nutrient utilization. The relative weights of the liver and thyroid were significantly increased in rats given ⩾75 mg Dithane/kg body weight, and those of the kidneys, adrenals and testes were significantly increased in the two highest dose groups. The serum cholesterol level was increased significantly in groups given ⩾75 mg/kg, and doses of 113, 169 or 253 mg/kg caused the elevation of the triglyceride content of the liver. The two highest doses of Dithane decreased the detoxicating capacity of the liver. The function of the thyroids was impaired even by very small doses of Dithane: at a dose of 10 mg/kg body weight the quantity of iodine stored in the thyroids was decreased by 20%. At doses of ⩾50 mg/kg statistically significant decreases in thyroid iodine content were observed. Histological examination of the thyroids showed dose-dependent hyperplasia in rats treated with Dithane.

Effects of amiodarone therapy on thyroid iodine content as measured by x-ray fluorescence.

Thyroid iodine content (TIC) was measured by x-ray fluorescence in 68 patients who had received amiodarone treatment for varying intervals (1 g/week for 1-120 months). Thirty-six patients were euthyroid; the mean TIC of the patients (n = 15), who had been treated for less than 12 months was 30 +/- 19 (+/- SD) mg, twice the normal mean value (14.6 +/- 5.0 mg), and it was 39 +/- 17 mg in those (n = 16) who had been treated for 12-60 months and 29 +/- 6 mg in those (n = 5) who had been treated longer (greater than 60 months). Nineteen patients were hyperthyroid and had elevated TIC values. Of them, 6 patients had a goiter; their TIC (50 +/- 19 mg) was not significantly different from that of the hyperthyroid patients with no goiter (55 +/- 29 mg), but they became hyperthyroid more rapidly. Thirteen patients were hypothyroid; none had TIC values above the normal range, and it was below 2.5 mg in 5 patients. A sequential study was undertaken in 11 euthyroid patients who had no detectable antithyroid antibodies. TIC did not increase during treatment in 2 patients; both developed hypothyroidism, which was transient in 1 despite continuation of amiodarone treatment. The TIC initially increased during amiodarone treatment in the other 9 patients, leveling off at the end of the first year. The TIC rose well above the upper limit of the normal range in 4 patients, of whom 2 became hyperthyroid during the second year of treatment. TIC remained within the normal range in the other 5 patients, of whom 3 became hypothyroid after 12-24 months of treatment (1 subclinical, 2 overt). Although the TIC was significantly higher in the patients with hyperthyroidism than in the patients who remained euthyroid, the TIC test cannot be used to predict the occurrence of hyperthyroidism. The latter must be diagnosed on the basis of clinical symptoms and a frank elevation of serum thyroid hormone levels. Conversely, patients whose TIC values do not increase during treatment or remain within the normal range should be considered at risk for hypothyroidism.

Effects of maternal iodine deficiency on thyroid hormone economy of lactating dams and pups: maintenance of normal cerebral 3,5,3'-triiodo-L-thyronine concentrations in pups during major phases of brain development.

Female rats were fed a diet with a low iodine content (LID), or the same LID supplemented with KI, and mated. Fetuses were obtained at 17 and 21 days of gestation, or pups were killed at different ages after birth. The dams on LID were markedly iodine deficient and developed a large goiter. Their thyroidal iodine content was only 4% of that of LID + I dams. The iodine deficiency of the LID mothers was severe enough to result in very low plasma T4 levels and in hepatic and cerebral T3 deficiency, despite normal circulating levels of T3. The fetuses from LID dams had low concentrations of iodine in their placentas and thyroid glands, and were deficient both in T4 and T3 in all tissues studied, including the brain. After birth, however, suckling LID pups were able to increase the plasma T4 to levels which were higher than those found in either LID fetuses or in adult LID progeny, although plasma T4 was always lower than in age-paired LID + I animals. This increase in T4 was probably due to an approximately 5-fold increase in iodine intake while suckling. Milk from LID mothers was found to contain 22% of the amount of iodine found in milk from LID + I dams, in contrast to their iodine intake, which was about 4% that of the LID + I rats. Cerebral T3 levels were the same for LID and for LID + I pups throughout most of the postnatal period of brain development. This finding might explain the difficulties encountered in obtaining an experimental model of neurological cretinism in rats.

Fetal brain development in response to iodine deficiency in a primate model ( Callithrix jacchus jacchus)

The common cotton-eared marmoset ( Callithrix jacchus jacchus) has been used for the first time as a primate model to study the effects of dietary iodine deficiency on fetal brain development. Paired male and female marmosets were fed a low-iodine diet of maize, peas, meat meal, Torula yeast, maize oil and added vitamins, minerals and amino acids for 6 months before mating. Offspring from first and second pregnancies were compared with offspring from control marmosets fed the same diet but supplemented with iodine. Severe iodine deficiency in the fetus at birth was evident by reduced plasma thyroxine levels, increased plasma thyroid stimulating hormone levels, increased thyroid weight and reduced thyroid iodine content. Thyroid histology revealed hyperplasia, hypertrophy and absence of colloid material in the follicles. Iodine deficiency caused a reduction in the weight of the fetal brain and in particular the cerebellum. Brain cell number was reduced in the cerebellum and brainstem but cell size was reduced in the cerebral hemispheres. Histology of the brain revealed morphological changes in the cerebellum and cerebral hemispheres. In the cerebellum there was: an increase in the thickness of the external germinal layer indicative of impaired cell acquisition; a decrease in total area; a decrease in molecular layer area; and an increase in Purkinje cell (Pc) linear density due to a reduction in the length of the Pc line. The decrease in molecular layer area and increase in Pc linear density imply diminished ascending and lateral extension of Pc dendrites. Changes in the cerebral hemispheres consisted of an increase in the density of neuronal cell bodies in the granular band and a decrease in synaptic counts in the layer between the pia mater and supragranular band of the visual cortex. Offspring from second pregnancies compared to those from first pregnancies were more severely affected and associated with lower plasma levels of maternal and fetal thyroxine. These findings indicate the importance of maternal and fetal thyroid function in relation to fetal brain development in the primate.

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

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 micrograms/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.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid iodine content and serum thyroglobulin: cues to the natural history of destruction-induced thyroiditis.

Twenty-eight patients with destructive thyroiditis were followed to study the natural history of healing of thyroid gland injury. All had sequential measurements of thyroidal iodine [127I] content by fluorescent scanning (normal mean, 10.1 mg), 17 had serial serum thyroglobulin (Tg) measurements (normal, less than 21 ng/ml), and 13 had perchlorate discharge studies during the recovery phase. Seventeen patients had painful subacute thyroiditis (SAT), 9 had painless thyroiditis with thyrotoxicosis (PTT), and 2 had postpartum thyroiditis with thyrotoxicosis (PPT). Thyroidal iodine content decreased from a mean of 9.8 to a nadir of 3.8 mg in patients with SAT and from 8.5 to a nadir of 3.5 mg in patients with PTT. Mean serum Tg concentrations were highest (approximately 165 ng/ml) in both groups 1-3 months after the onset of symptoms. Abnormalities in both 127I content and Tg levels persisted for 2 or more yr in some individuals. No patient had detectable Tg antibodies by hemagglutination, but low titers were detected intermittently by sensitive RIA in 5 PTT patients. Microsomal antibodies were positive in only 1 of 16 SAT patients, but in 4 of 7 PTT patients and in both PPT patients. Three patients had positive perchlorate discharge tests (2 of 8 with SAT, 0 of 4 with PTT, and 1 of 1 with PPT). Permanent hypothyroidism occurred in 3 patients (2 with PTT; 1 with SAT and positive antibodies), but did not correlate with perchlorate results. HLA typing and serum immunoglobulin measurements were not useful for predicting the clinical course. These data indicate that several years may be necessary for complete resolution of destructive thyroiditis; many patients have evidence of thyroid injury persisting long after serum thyroid hormone and TSH levels become normal.

Computed tomographic determination of thyroid iodine concentration in an endemic goiter area

We determined the CT density of the thyroid gland in 60 patients with normal thyroids and 176 patients with various thyroid disorders. The density was 75 +/- 6.2 H.U. in normal thyroids, which was markedly higher than in goiters (66 +/- 6.0 H.U.), while there was a considerable further decrease in patients with immunogenic hyperthyroidism, the density being 48.5 +/- 7.9 H.U. The thyroids of patients with nonimmunogenic hyperthyroidism differed from these by virtue of a significantly greater density, 79.8 +/- 12.5 H.U. The clinical importance of CT investigation of the thyroid is its ability to distinguish rapidly between immunogenic hyperthyroidism without ocular symptoms and the (mostly iodine induced) non-immunogenic form. There is a linear correlation between CT density and iodine concentration in the thyroid tissue; this was determined in surgical specimens from 17 patients. Iodine concentration in the thyroid, as well as the iodine content of the whole gland, can thus be calculated from the measured CT density at any time by estimating the volume of the gland with ultrasound and combining this value with the measured iodine concentration. The results correlate well with those found using the x-ray fluorescence method.

Serial thyroid iodine content in hyperthyroid patients treated with radioiodine.

X-ray fluorescent scanning was used to measure initial thyroidal iodine content in 64 patients diagnosed as being hyperthyroid and selected for I-131 therapy, and serially in 48 of these patients after therapy in an attempt to determine those patients that were at high risk of becoming hypothyroid. Iodine content fell rapidly after therapy, reaching a nadir at about three months. Based on the population studied, the chance of early hypothyroidism (within 12 months) is about 80% if the iodine content measured at three months is less than 2 mg. If the iodine content is greater than 2 mg, the chance is only about 14%. The serial measurement of thyroidal iodine content (with x-ray fluorescent scanning) may allow early identification of those patients at high risk of developing permanent hypothyroidism following a therapeutic dose of I-131.

T-2 mycotoxin intensifies iodine deficiency in mice fed low iodine diet.

Mice were depleted of iodine and fed a 125I-labeled low iodine diet. After they developed isotopic equilibrium they were given T-2 mycotoxin, in doses 34% to 14% of LD50/day for 4 to 12 days. In all cases T-2 toxin caused loss of thyroid iodine from which the animals recovered when the T-2 toxin was stopped. When iodine intake was adequate, the T-2 toxin had no statistically significant effect on the thyroid iodine content. Since T-2 toxin is known to block the initiation of some protein synthesis, it may block thyroglobulin synthesis, and, in stimulated thyroids, limited hydrolysis may continue. Therefore, when the thyroids were stimulated and thyroglobulin was depleted, a blockade of thyroglobulin synthesis may have caused further depletion of thyroidal iodine.

Relationship between serum thyroglobulin and intrathyroidal stable iodine in human simple goitre.

Serum thyroglobulin levels are increased in many patients with simple goitre. This increase has been attributed to the release of thyroglobulin (Tg) from the colloid of necrosed follicles. To test the hypothesis that increased serum Tg could be related to the low intrathyroidal iodine concentration [I], the main cause of nontoxic goitre, these two variables were measured in 91 euthyroid goitrous patients and compared to serum free T3 and free T4 levels as well as thyroid weight. Thyroid iodine concentration was estimated from the X-ray fluorescence measurement of intrathyroidal iodine stores and from the weight of the gland estimated by planimetry. Serum Tg levels, the free T3/T4 ratio and thyroid weight were negatively correlated to [I] (Spearman's coefficient of correlation = - 0.44 (P = 0.001); -0.30 (P = 0.006); -0.33 (P = 0.001), respectively). Tg levels were also positively correlated to the T3/T4 ratio (R = 0.28, P = 0.008) and to the weight of the gland (R = 0.37; P = 0.001). These data suggest that, in simple goitre, increased serum Tg concentrations are partly related to the reduced concentration of iodine in goitre tissue (as are an increased T3/T4 ratio and the size of the goitre) and is not only the reflection of follicular necrosis.

Influence of the HLA-DR4 antigen and iodine status on the development of autoimmune postpartum thyroiditis.

HLA-A, -B, and -DR antigens were determined in all 50 women with a serum thyroid microsomal hemagglutination antibody (MsAb) titer equal to or greater than 1:100 in the first trimester of pregnancy in a population of 733 pregnant women. The DR4 antigen was found in 58.0% of the women compared to 33.7% in control subjects, which corresponds to a relative risk of 2.71 (P less than 0.01 by X2 test). The MsAb-positive women were examined regularly during the year after delivery for the development of thyroid dysfunction. The DR4 antigen frequency was found to be even higher, 69.0% (relative risk = 4.36; P less than 0.001), among the 29 women who developed hypothyroidism in the postpartum period. No other HLA antigen deviations were found among those 15 hypothyroid women in whom an initial thyrotoxic phase occurred before hypothyroidism. The B8, DR3 haplotype was found in 3 of 5 women who developed Graves' thyrotoxicosis alone. Urinary iodine excretion measured in some MsAb-positive women 3 (n = 19) or 6 months (n = 29) postpartum, respectively, was compatible with leakage of thyroid iodine during the initial destruction-induced thyrotoxic phase of postpartum thyroiditis, followed by low iodine excretion during the subsequent hypothyroid phase. We conclude that genes coding for the DR4 antigen may have a regulatory influence on MsAb production, which in turn affects the development of postpartum hypothyroidism. Thyroid iodine content and iodine intake also may have an impact on the severity of the thyrotoxic and the hypothyroid phases of autoimmune postpartum thyroiditis.

Influences of feeding of high-iodine eggs on hypo- and hyperthyroid rats.

The effects of the feeding of high-iodine eggs to rats with an abnormal thyroid status were investigated. Rats were fed for one week on a commercial diet supplemented with propylthiouracil (PTU) (10 mg/100 g diet) or thyroxine-Na (240 micrograms/100 g diet) respectively, to induce hypo- or hyperthyroidism, and then further fed for 4 weeks on the respective drug-supplemented diets, containing 1% (w/w) of either ordinary or high-iodine egg powder. Control (euthyroid) rats were maintained on the commercial diet. The induction of a hypothyroid state resulted in thyroid hyperplasia, with decreased thyroid iodine content, altered serum thyroid relating hormone levels (increased TSH and decreased T3 and T4), elevated serum total cholesterol and reduced serum triacylglycerol (TG) levels, and also increased muscle and adipose tissue lipoprotein lipase (LPL) activities. In contrast, in the hyperthyroid animals, thyroid atrophy, as well as decreased serum TSH and increased T3 and T4 levels, was associated with reduced serum total cholesterol level and muscle LPL activity. There were no essential differences between animals given high-iodine and ordinary eggs in either hypo- or hyperthyroid state, although the effects of PTU treatment on the thyroid and serum TG level appeared to be slightly lesser in rats given high-iodine eggs than in those given ordinary eggs. It is concluded that high-iodine eggs did not have any side-effect on either hypo- or hyperthyroid rat in this study.