Thyroidal 131I Uptake Research Articles

Thyroid 131I Uptake Measurement with a Scintillation Camera

Thyroid 131I Uptake Measurement with a Scintillation Camera

Serum thyrotropin levels of natives in Sarawak, Borneo Island.

ABSTRACT A survey of endemic goiter was carried out on natives of Borneo Island, where dietary iodine was deficient. The prevalence of goiter and size of goiter were positively correlated to the age of the subjects. The increase in cumulative prevalence (vide infra) was highest between age 10 and 30, with annual increment approximately 0.5%. Serum TSH was not elevated in all subjects without goiter (less than 5 μU/ml). Mild elevation of TSH up to 20 μU/ml was found in 18% of goitrous subjects, while PBI, T3 resin sponge uptake and free T4 index were not different between goitrous and non-goitrous subjects. When a comparison was made among goitrous subjects, TSH was not significantly elevated in the younger age group in which goiter development was considered active. TSH levels do not correlate with degree of goiter. High 24-hr thyroidal 131I uptake, over 50%, was observed in 71% (15/21 cases) in the face of normal TSH levels. Hence, our findings suggest that TSH seems to be responding to iodine deficiency...

Thyroid hormone secretion rate in the lactating rat.

Summary. Thyroid secretion rate (TSR) was determined in lactating and non-lactating rats by the thyroxine substitution and `direct output' methods. In lactating rats, apparent TSR as determined by the substitution method was significantly greater than that of controls when dietary iodine was deficient. By the direct output method, TSR was significantly reduced even when dietary iodine was adequate. It is concluded that the substitution method measures the physiological demand for thyroid hormone, which is greater during lactation, but represents true TSR only if iodine supplies are adequate. Results obtained by the direct output method show the actual TSR to be significantly reduced both during lactation and when dietary iodine is limited. Mean thyroid acinar cell height significantly increased as thyroidal iodine was depleted. It is concluded that, during lactation, TSH was elevated but iodine was insufficient to support the demand for thyroid hormone. The low serum T4 level observed in lactating rats, as determined by a competitive binding method, supports these conclusions. Analysis of the methods of computation of TSR by direct output showed that (1) as thyroidal iodine supplies were depleted, thyroidal iodide accumulation became more efficient, (2) the iodine-deficient thyroid recycled a greater percentage of the available iodine, (3) thyroidal 131I uptake was reduced in lactating rats, (4) total thyroidal iodine was inversely correlated to its release rate (K4) from the thyroid, and (5) thyroidal iodine, and not K4, was the major factor influencing TSR under these experimental conditions.

Recovery of initially suppressed thyroidal radioiodine uptake during long-term antithyroid treatment of euthyroid volunteers and hyperthyroid patients.

ABSTRACT Carbimazole in daily doses of either 15 or 45 mg acutely depressed the thyroidal 131I-uptake (measured at 2, 8 and 24 hours after administration of the tracer) in 34 healthy human volunteers. Fourteen of these subjects were kept on carbimazole for four weeks. A gradual recovery of the radioiodine uptake was observed in every individual. By the end of the fourth week the 24 h uptake had risen by 100% over the value observed with acute suppression in the 15 mg carbimazole group (i. e. from 5.7 to 11.4%) and by 500% in the 45 mg carbimazole group (i.e. from 2.7 to 15.8%). The corresponding figures for the 8 h uptake were 100 to 250% and for the 2 h uptake 40 to 60%. In three individuals the uptake in the fourth week of carbimazole treatment was distinctly higher than the pretreatment control values. Thus the acute suppression of a complete blocking dose of carbimazole on thyroidal radioiodine uptake is partially or even totally overcome within a few weeks of chronic treatment. It is therefore possible, in human subjects, to produce experimentally a high thyroidal radioiodine uptake by antithyroid drug treatment alone, in the absence of concomitant severe iodine deficiency. This finding may have a bearing on the interpretation of radioiodine studies carried out on endemic goitre. Comparable findings were obtained in 23 hyperthyroid patients treated with carbimazole for a mean of 28 weeks. In order to elucidate the mechanisms responsible for the later rise of an acutely carbimazole suppressed uptake, the serum PB127I and TSH concentration was measured at weekly intervals. Whereas the PBI fell both in this and in another series of volunteers by the end of the fourth week of carbimazole treatment, no significant change in serum TSH concentration was measurable by radioimmunoassay. Nevertheless, the hypothesis is put forward that a biologically significant increase in serum TSH concentration had occurred, which was not detectable by the radioimmunoassay techniques available at the present time. There are indeed reasons to suspect that biologically important variations in TSH secretion may occur which fail to bring the serum TSH concentration beyond the normal range defined by radioimmunoassay.

Environmental temperature and thyroid function in the green water snake, Natrix cyclopion

A direct relationship was found between environmental temperature and thyroid gland activity in the green water snake, Natrix cyclopion cyclopion. Thyroid 131I uptake was found to be responsive to differences in acclimation temperature. At 32° there was a maximum 131I uptake of 29.7% on day 7 after injection of the isotope. At room temperature (21–24°) there was a peak uptake of 26.0% on the twelfth day after injection, and at 15° there was a maximum uptake of 6.6% on day 6.

Maternal-fetal endocrine interrelations: effects of synthetic thyrotrophin releasing hormone (TRH) on the fetal pituitary-thyroid system of the rat.

The capacity of the fetal pituitary-thyroid system to respond to synthetic TRH (pyroGlu-His-ProNH2) was tested by administration of the hypothalamic hormone on the last day of gestation to intact and hypophysectomized pregnant rats whose thyroids were labeled with 131I 24 h previously. Significant decrease in the ratios of thyroid-blood radioactivity occurred in newborn of TRH-treated mothers. Consistent reduction (30–70 %) in thyroidal 131I uptake and increase in blood radioactivity (12–60%) were observed. Bioassays (stasis tadpole) revealed significant elevation in plasma TSH levels and reduced hormone content of the pituitary in pups of mothers receiving TRH. In utero injections of the hypothalamic hormone into fetuses produced a similar pattern of TSH change within 15 min. Sufficient TSH release occurred to induce histologic activation in the thyroids of spontaneously delivered offspring. The effect of TRH on TSH release by the fetal hypophysis appeared to be specific. No indication of any substantial influence on maternal and fetal pituitary-adrenal system was observed.

Endemic goiter in Sarawak, Borneo Island; prevalence and pathogenesis.

A survey for endemic goiter was carried out on Iban natives (Sea Dayak) in four districts along the Rajang River in Sarawak, Borneo Island.Among 608 subjects (271 males and 337 females) examined, 134 subjects (22 males and 112 females) were found to be goitrous, the prevalence of goiter being 8.1 for male and 33.2% for female. None were clinically hypo-or hyperthyroid, no cretinism was detected.Twenty-four hr. thyroidal 131I-uptake was 54.3±13.1 %(mean±S. D.) in goitrous subjects while 47.1±10.2% in non-goitrous (no statistical significance). Urinary excretion of iodine was 45±27μg per day in goitrous group and 49±25μg in nongoitrous group (no significance). Iodine content of drinking water was extremely low in all four districts, the lowest one being obtained from region in which the prevalence of goiter is highest. Thyroid parameters such as PBI, T3 resin sponge uptake and cholesterol were all within normal limits. Anti-thyroid antibodies were not demonstrated in sera from either goitrous or nongoitrous subjects. KSCN discharge test was positive in two cases in a single family, among 33 cases studied.Experimental feeding of cassava on our expedition members for two weeks did not show any change in thyroid parameters including KSCN discharge test.It is thought that iodine deficiency is probably a major causative factor of endemic goiter in Sarawak, Borneo Island. Other factors such as organification defect or defective thyroxine binding proteins might have some role in individual cases.

Paradoxical stimulation of thyroid function by cortisone in the rat.

We have studied the effect of cortisone on 131I metabolism of highly stimulated rat thyroids. Rats were fed a low-iodine diet (LID) containing 0.15% propylthiouracil (PTU) for 7 days. The PTU diet was withdrawn on day S and LID alone fed for another 4 days. Half of the animals received 5 mg cortisone daily from day 6 to the day of autopsy. The 4-hr thyroid 131I uptake was consistently higher in the cortisone-treated rats than in the controls after PTU withdrawal. Similar differences between cortisone and control groups were seen in acutely nephrectomized rats and in those hypophysectomized and maintained with TSH. Higher T3*/T4* and MIT*/DIT* ratios were found in the digested thyroids of the intact cortisonetreated rats than in the controls. The T/S (TcO4–) was significantly higher in cortisonetreated animals than in controls. A single injection of cortisone did not affect the 4-hr thyroid 131I uptake in PTU-withdrawal rats, but decreased the 12 and 24-hr 131I accumulation. The increase in thyroid 131I me...

Rebound phenomena in thyroid function after withdrawal of propylthiouracil in growing chicks

Changes in thyroid function after withdrawal of PTU in chicks were imvestigated with particular reference to the biosynthesis of thyroid hormone. The weight of thyroid, as well as the ratios of I −∗/MIT ∗ and MIT ∗/DIT ∗, increased when the chicks were maintained on diets which contained PTU at levels of 0.01% and 0.05% for 21 days. Withdrawal of PTU from the diet resulted in a gradual decrease in the weight of thyroid. A distinct rebound phenomenon in thyroidal uptake of 131I was observed at day 3 after withdrawal. Rebound phenomena were not found in I −∗/MIT ∗ and MIT ∗/DIT ∗ ratios and these ratios were restored rapidly to a normal level. The most striking rebound was observed in T 4 ∗ biosynthesis, differing from the rat in which rebound of T 3 ∗ was the most remarkable.

The effect of iodine deficiency and suppression of TSH secretion on radioiodine labelled thyroxine and triiodothyronine in the thyroid of rats.

ABSTRACT It has been suggested that TSH stimulation of the thyroid gland is accompanied by an alteration in the ratio of newly synthesized thyroxine (*T4)1)/triiodothyronine (*T3) in favour of *T3. Evidence in support of this hypothesis is provided here by the finding that suppression of TSH secretion in rats alters this ratio in the other direction, i. e. in favour of *T4. Thus, endogenous TSH stimulation was increased for 4 weeks by iodine deficiency. Its suppression was performed by the administration of T3, using a dose of 0.05-0.25 μg/100 g body weight which was injected subcutaneously every 12 hours for three days. The effect of TSH stimulation and suppression could be assessed from the following parameters: thyroid weight and histology, thyroid 131I uptake, 131I conversion ratio, hormonal iodine concentration, and TSH level in the plasma. After iodine deficiency the ratio of *T4/*T3 in the thyroid gland changed in favour of *T3. This may compensate for the iodine deficiency, since the oxygen consumption and the heart rate of the animals remained in the normal range. After suppression the ratio of *T4/*T3 changed in the opposite direction, i. e. in favour of *T4. The extent of the suppression of *T4 and *T3 was dependent on the suppression dose used.

Nicotinamide HCl and thyroid radioiodine metabolism in mice: effects due to acid.

Previously we described effects of nicotinamide in vivo on mouse thyroid pyridine nucleotides and radioiodine kinetics. The nicotinamide was used as the hydrochloride, so we have re-evaluated those findings to take account of possible influences of the pH of the solution. Acid and neutral solutions of nicotinamide and nicotinic acid enhanced the thyroid concentration of NAD 2- to 3-fold; HCl, 6-amino-nicotinamide and isoniazid had no effect. In mice previously injected with 125I increases in blood 125I followed 2 hr after injection of HCl and acid solutions of nicotinamide, 6-amino-nicotinamide and quinolinic acid; NaOH and neutral solutions of nicotinamide and quinolinic acid failed to increase blood 125I. Thyroid uptake of 131I was enhanced by HCl, NaOH and acid (but not neutralized) solutions of nicotinamide HCl and nicotinic acid; in hydrolysates of thyroids with uptake enhanced by acid nicotinamide and HCl there was an increase in the proportion of 131I in iodotyrosines and a decrease in 131I in iodo...

Reduced thyroid activity in Jamaicans.

SUMMARY The results presented demonstrate reduced thyroid activity in euthyroid Jamaicans. In 15 subjects, thyroid clearance of 131I was 13·0 ± 8·8 (s.d.) ml/min, and renal clearance was 20·6 ± 9·7 ml/min. In 205 healthy volunteers the 24 h 131I thyroid uptake averaged 13·8% and in 60·9% the uptake was less than 10% of the dose. Urinary excretion of 131I was correspondingly high. However, excretion of stable iodine in urine averaged only 62·0 μg/day. Thyroid secretion rate (TSR) calculated in a group of subjects with complete collection of urine was 12·0 μg I/day in women and 11·4 μg I/day in men. Protein-bound iodine (PBI) values in 50 subjects were 5·9 ± 1·3 μg/100 ml. Uptake of tri-iodothyronine by red blood cells also gave low values. The apparent discrepancy between low TSR and normal PBI is discussed. These findings, together with other reported values, indicate reduced thyroid activity in the tropics. It is argued that reduced metabolism is probably secondary to lower thyroid activity.

Adaptation of thyroid function to iodine intake in Buenos Aires.

The thyroidal 131I-uptake of inhabitants of Buenos Aires is higher than that obtained in areas where iodine provision is adequate. The conversion ratio and the thyroid clearance of iodine are also high. Urine iodine and iodine content of water are low, as compared with values obtained in areas where there is no endemic goiter. Young men born and raised in Buenos Aires city have a 2.35% incidence of goiter of degree I, according to the classification of WHO. When thyroid enlargements intermediate between degree 0 and I were taken into account, a further 17.9% of thyroid enlargement was recorded. These data point to a low iodine intake in Buenos Aires, the magnitude of which parallels that of the metabolic and morphologic changes in the thyroid gland. These changes, in turn, suggest that some adaptive mechanisms have maintained normal hormonal secretion. The suggestion is made that the classification of goiter provided by WHO should be revised, since it does not record goiters of moderate although significant size.

Effect of reduced food intake on thyroid cell height and goitrogenic response in rats.

SUMMARY Adult rats in groups of ten were maintained variously on full, half and quarter food intake. Some were given plain drinking water ad libitum, others were given a goitrogenic challenge of 0·1% aminotriazole (ATA) in the drinking water. Food and fluid consumption were measured daily. The animals were killed after 3 weeks for measurement of thyroid and body weight. The thyroids were histologically examined and epithelial cell height was measured. Another series of rats on normal food intake were given ATA solutions of various concentrations to drink and the efficacy of the concentrations to depress a 16 h thyroid uptake of 131I was measured. The results showed a reduction in average thyroid cell height parallel to the degree of starvation in the non-ATA treated groups and a reduction in goitrogenic response to equivalent challenge with ATA of about 15% in the half-fed animals and 20–25% in the quarter-fed animals. It is suggested that, in adapting to caloric restriction, higher centres depress the thyrotrophic hormone releasing factor response of the hypothalamus to a fall in circulatory thyroid hormone concentration. The degree of reduction in goitrogenic response might be regarded as a quantitative index of this depression.

Effects of chronic excess salt feedin: demonstration of normal thyroid function in salt-fed dogs with hypercholesterolemia.

SummaryThe hypercholesterolemia associated with chronic excess salt feeding is not due to hypothyroidism. As shown by thyroidal 131I uptake, by plasma protein-bound iodine concentrations, and by hi...

Thyroid Function in Euthyroid Jamaicans

ABSTRACT Thyroid function has been investigated in 32 hospitalized euthyroid Jamaicans. The in vivo investigations performed were measurement of 2½, 4 and 24 hr thyroidal uptake of 131I, thyroidal and renal clearances of radioiodide, absolute iodide uptakes and, in 6 subjects, radiothyroxine turnover studies. Thyroxine binding globulin and prealbumin capacities were measured in a small number of cases. Results obtained in all these investigations agreed well with those found in temperate climates and are at variance with a previous finding of low 24 hr thyroidal uptakes of 131I in euthyroid Jamaicans, associated with a normal serum protein-bound iodine.

Influence of the long-acting thyroid stimulator (LATS) on radioiodine-labelled thyroxine and triiodothyronine in the thyroid of mice.

The influence of a LATS-rich serum concentrate on the following parameters of thyroid function in mice fed an iodine-rich diet has been investigated: thyroid weight and histology, thyroid 131I uptake and the distribution of *T4 2 and *T3 in the thyroid at different times after radioiodine administration. All these parameters were influenced by LATS. Thyroid weight, histological changes, and the percentage of *T3 and *T4 increased in dependence on the LATS dose administered. The labeling of T3 was more stimulated than that of T4. There was a similar incline of the dose-response curve of LATS in the McKenzie assay on the one side and of the percentage of *T3 in the thyroid on the other. The results support the view that LATS and TSH may act on a similar subcellular level and that the change of the *T4⁄*T3 ratio in favor of *T3 is a general reaction after stimulation of the thyroid gland. (Endocrinology 87: 632, 1970)

Endemic goiter in Greece: Effects of iodized oil injection

Iodine metabolism has been studied in patients with endemic goiter in Greece following the injection of iodized oil, which reduced the size of the glands, more markedly in the diffuse goiters than in the nodular ones. Injection of labeled iodized oil resulted in a very slow diffusion from the injection site, and the local radioactivity decreased with a mean biological half-life of 70 days. Serial studies over 12 months in 34 patients with endemic goiter injected with 1 ml. of iodized oil showed an increase in the Plasma Inorganic Iodine (PII) and the urinary iodine, and a decrease in the thyroidal 131I uptake and clearance. The excess urinary iodine was in inorganic form. Extrapolation of the data suggests that a 1 ml dose would give adequate prophylaxis from iodine deficiency for 25 months. Following the iodized oil injection, the Absolute Iodine Uptake (AIU) by the thyroid increased, and so did the BEI and serum thyroxine (Tetrasorb) values whereas the Triosorb test did not show consistent results. The serum PBI increased out of proportion to the BEI, the difference being accounted for by the presence in the circulation of an iodinated albumin-like protein.

Influence of lymphocytic thyroiditis on iodine metabolism in the beagle.

SummaryTracer studies of thyroidal 131I metabolism were conducted in beagles some of which had lymphocytic thyroiditis. The percentage of each thyroid lobe represented as epithelium, colloid, and stroma, as well as the severity of the lesions, was determined by microscopic examination. The high level of iodide in the commercial diet fed resulted in low thyroidal 131I uptake values in all animals. Dogs with severe thyroiditis had biological half-times (BT 1/2) of 131I significantly shorter than dogs with mild or no lesions. The maximum thyroidal uptake of 131I was significantly lower and also occurred earlier in dogs with severe thyroiditis. Fourteen months after one thyroid lobe was removed the BT 1/2 of 131I was shortened compared to values obtained in the intact dog.There is little colloid in thyroid glands affected with severe lymphocytic thyroiditis; hemithyroidectomy also results in a reduction of the relative amount of colloid with a corresponding increase in the percentage of epithelium in the oppo...

Apathetic thyrotoxicosis: A distinctive clinical and laboratory entity.

Nine patients with apathetic thyrotoxicosis were studied over a 1-year period and compared with 29 typical hyperthyroid subjects. These apathetic patients were significantly older and had a longer duration of symptoms and greater weight loss. The study group had a rather typical apathetic, placid, or depressed appearance often thought to represent "old age depression." Cardiovascular symptoms, atrial fibrillation, and congestive heart failure were common. They typically had evidence of a moderately severe proximal myopathy. Thyromegaly, although usually present, was not prominent and was usually multinodular. There was a striking absence of eye signs generally associated with thyrotoxicosis, and blepharoptosis was frequently observed. Although the protein-bound iodine and 131I thyroidal uptake were not markedly elevated, the diagnosis was easily established by utilizing the usual tests of thyroid function and integrating the results with the rather typical clinical features.