Low Iodine Diet Research Articles

I-131 accumulation by the lactating rat mammary gland.

The mammary glands of lactating rats fed a low-iodine diet accumulated 50% of an injected I131 dose or five times as much as the thyroid gland and twice as much as excreted by the kidneys in 17–24 hr. Rats which accumulated greater amounts of I131 in their mammary glands had significantly lesser thyroidal I131 uptakes. KClO4 and methimazole significantly reduced accumulation of I131 in milk, KClO4 being the more potent. Methimazole acted primarily in reducing the binding of I131 to milk protein. The concentration of I131 in milk, trichloroacetic acid-precipitable I131 in milk and in plasma, and ratio of milk I131 to plasma I131 were significantly reduced by the addition of iodide to the diet. The amount of I131 in the milk was not correlated with the amount of milk secreted. Exogenous thyroxin inhibited thyroidal I131 uptake but did not influence accumulation of I131 by the mammary gland. Injection of thyrotrophin restored thyroidal uptake of I131 but did not affect accumulation of I131 by the mammary gland.

Kinetic analysis of thyroidal iodide concentration in hypophysectomized rats fed high or low iodine diets.

Kinetic analysis of thyroidal iodide concentration in hypophysectomized rats fed high or low iodine diets.

EFFECTS OF DIETARY IODINE ON THE UTILIZATION OF RADIOACTIVE IODIDE BY THE RAT

Sprague–Dawley rats were fed on diets ranging from 40 μg I/kg to 3885 μg I/kg. Single doses of iodide-131 were injected intraperitoneally into each of the rats. In vivo measurements of radioisotope levels were made at intervals for 11 to 15 days over the neck and thorax. Thyroidal I131 curves were obtained by using a fraction of the thoracic counts to correct for the extrathyroidal component of the neck counts. Animals on low-iodine diets concentrated I131 in their thyroids more rapidly and to greater peak values, had lower protein-bound iodine (I127) concentrations, and lower total thyroidal iodide (I127) content than did rats in the high-iodine groups. An attempt was made to compensate the thyroidal counts for the continuing decrease in the concentration of iodide-131 in the plasma. From this attempt was derived the "thyroidal index", a parameter which may be related to the rate of exchange of the total thyroidal iodine stores. Biological half-life values (I131 in thyroid gland) for the low-iodine groups were larger than those for the high-iodine animals. The hypothesis is advanced that, at least for the conditions reported here, the biological half-life does not adequately reflect thyroidal activity; exchange of iodine between the rat and its environment is considered to be the more important factor in controlling the numerical value of this parameter.

Goitrogenic action of thyroxine administered with propylthiouracil.

ABSTRACT Rats were fed chow or a low iodine (standard) diet containing 0.02% propylthiouracil (PTU) for a year or longer. Over a critical range of dosage, 1-thyroxine (T4) potentiated the goitrogenic effect of PTU. The effect was greater with a chow diet than with the standard diet. Part of this difference could be attributed to the presence of more iodide in the chow, as iodide added to the standard diet increased the size of the goitres produced. The maximum effect was produced when 25 μg% or less of T4 was administered, and in high dosage (125 μg% in diet) inhibition of goitrogenesis occurred. Similar degrees of goitrogenesis took place when 0.02%. 0.05% or 0.125% PTU were fed supplemented with one concentration of T4. Thus the potentiation of goitrogenesis is related to the intake of thyroxine itself, and can most likely be explained by the action of the hormone on the adenohypophysis or higher centres, or on functions of the thyroid gland.

Studies on the production of high radioiodine uptake goiter with propylthiouracil.

Rats were fed a low iodine diet with propylthiouracil added at a level of from 2×1O−5 to 15×lO−2%. In 2 of the 3 experiments, half the animals received supplementary iodine. In no instance was the thyroid enlargement in propylthiouracil-fed rats significantly greater than that of the respective controls without a concomitant lowering of radioiodine uptake. Iodine supplementation favored the formation of diiodotyrosine and T4 over monoiodotyrosine and T3. Propylthiouracil inhibited formation of diiodotyrosine and T4 to a greater extent than it did monoiodotyrosine and T3. Supplementary iodine decreased goitrogenesis but increased the inhibitory effects of propylthiouracil on radioiodine uptake and on formation of diiodotyrosine and T4.

Neural control of the thyroid gland: studies on the role of extrapyramidal and rhinencephalon areas in the development of the goiter.

Bilateral electrolytic lesions placed on the extrapyramidal—globus pallidum— area, and in the rhinencephalon—septal area—resulted in a marked release of thyrotropic hormone (TSH) both in goiter-free rats and in those with goiters induced by a low iodine diet. In some of the groups the average weight of the thyroid gland increased by 400%. The height of thyroid acinar cells, microfollicular hyperplasia, radioiodine (I131) uptake, I131 concentration in the thyroid, protein-bound radioiodine (PBI131), and I131 uptake by red cells were also noticed to increase. A parallelism was found to exist between most of the parameters in radioiodine metabolism and the weight of the thyroid and its histologic picture. These findings point to the presence of centers inhibiting TSH secretion in these areas, and are suggestive of the existence of other areas in addition to the anterior hypothalamus, which significantly interfere with TSH release.

Role of iodine, sodium chloride and antithyroid drugs in the development of goiter in the rat.

In an attempt to study the possible role of goitrogens, NaCl and iodine in the development of goiter, graded doses of methylthiouracil (MTU) and 2% of NaCl were given to rats fed low and relatively high iodine diets for 14 days. Small amounts of MTU produced goiter with normal or slightly high radioiodine uptake and suppressed triiodothyronine +thyroxine (T3 + T4) formation in animals fed a low iodine diet. NaCl was also goitrogenic and suppressed T3 + T4 synthesis in animals fed a low iodine diet. Although significant goiter occurred with MTU and NaCl treatment, serum PBI was fairly normal in all groups. However, these goitrogenic and suppressive effects on thyroidal T3 + T4 formation by small amounts of MTU or NaCl did not appear in animals fed a relatively high iodine diet. Even when large amounts of MTU were given, the increase in thyroid size and the depression of T3 +T4 formation were significantly greater in animals fed a low iodine diet than in those on a relatively high iodine diet. It is suggest...

STUDIES ON THE INHIBITORY ACTION OF EXCESS IODIDE ON THYROIDAL RADIOIODINE RELEASE IN THE RAT

In an attempt to study a thyroid state in which excess iodide would inhibit thyroidal radioiodine release, normal and hemithyroidectomized animals were fed a low and high iodine diet for 7 days. During the measurement of thyroidal radioiodine release, animals were injected with or without graded doses of propylthiouracil.In normal rats fed a low iodine diet, thyroidal radioiodine release was inhibited by excess iodide when small amounts of propylthiouracil (5mg) were injected, while in high iodine diet fed animals, thyroidal radioiodine release was not inhibited by excess iodide in any of the experimental conditions studied.In hemithyroidectomized and low iodine diet fed animals, thyroidal radioiodine release was inhibited significantly by excess iodide regardless of the dosesof propylthiouracil used, but the inhibition was most marked when 5mg of propylthiouracil were given. However, in the animals similarly treated but fed a high iodine diet, thyroidal radioiodine release was inhibited only when small amounts of propylthiouracil were given.It is suggested that excess iodide inhibits thyroidal radioiodine release when the thyroid gland is overfunctioning.

Adolescent acne and dietary iodine.

<h3>Introduction</h3> The etiologic role of iodine as encountered in the diets of patients with adolescent acne vulgaris has long been of concern to physicians. Apparently because it has been unequivocably shown that iodine given as a medicine can cause an acneiform eruption, diets restricting foods and condiments with high iodine content have been prescribed for these patients with varying degrees of vigor by many physicians, including dermatologists. For example, the authors of several American dermatologic texts recommend restriction of iodized salt and/or "seafoods." Objective evidence supporting any attitude on dietary iodine for these patients is indeed sparse. The most extreme view encountered is that of Barefoot¹who felt that a group of patients with acne vulgaris on a low iodine diet were further benefited by the administration of nicotinic acid, which was supposed to "neutralize or counteract the aggravating factors of iodides." Owing to the paucity of solid evidence

A Goitrogenic Rat Diet Producing Normal Body Weight Gain.

SummaryBy using 40% of brewers type dry yeast as the principal protein source, a low iodine diet has been designed that supports a good rate of body weight gain and also produces large goiters in rats. This diet appears to have a positive goitrogenic effect, over and above that attributable to its low iodine content.

Circulating Thyroid Hormones in Domestic Birds

IT IS now known that at least two natural thyroid hormones are found in vertebrates—thyroxine (T-4) and triiodothyronine (T-4) and triiodothyronine (T-3) (Pitt-Rivers and Tata, 1959). Applying radiochromatography to thyroid gland hydrolysates of birds injected with I131, several workers have identified both T-3 and T-4 in chickens (Shellabarger and Pitt-Rivers, 1958; Vlijm, 1958; Frey and Flock, 1958; Mellen and Wentworth, 1959) and ducks (Tixier-Vidal and Assenmacher, 1958). Published information on the circulating hormones in birds is more scarce, however. Vlijm (1958), in a single experiment, demonstrated the presence of T-4 in chicken serum, but was able to detect T-3 only occasionally. Mellen and Went-worth (1959) were able to detect both radioactive T-3 and T-4 consistently in chicken plasma if the birds were pretreated with thiouracil and a low-iodine diet before I131 injection. They pointed out that hormonal radioactivity in the chicken plasma was weak compared to that in plasma…

Thyroid function in the rat during pregnancy and lactation.

1) Pregnant rats were fed 0.15% propylthiouracil (PTU) from the 10th to the 19th day of pregnancy and 1, 2, 3, 4 or 5 μg. T4 were injected daily during this time. The regression slopes of the thyroid weights were similar to those of the corresponding controls except that 2 μg. T4 produced less decrease in thyroid size in pregnant than in non-pregnant rats. 2) Pregnant rats were fed a low-iodine diet from the 10th to the 19th day of pregnancy and doses of T4 were administered during this interval as in 1). The regression slopes of the thyroidal I131 uptake of the pregnant and non-pregnant rats were identical but uptakes were consistently slightly lower at each point for the pregnant rats. 3) Following seven days of low-iodine diet, thyroidal I131 uptakes were determined at one to two day intervals from the 8th day of gestation to the 29th day of lactation. Uptakes were not statistically different from the controls until the 20th day of pregnancy when a marked drop of approximately 50% occurred which persis...

A Technique for Assay of Goitrogens in Feed

An assay procedure has been described which can be used to detect minute amounts (0.5–2 ppm.) of residues in tissues of goitrogen-fed animals. The technique described in rats consists in determining 24-hour I131 uptake after feeding the goitrogen (or tissues) for a period of 4 days and then comparing it with control I131 uptakes. A low-iodine diet, by enhancing I131 uptake, increased the sensitivity of the assay technique. By this method, tapazole at 0.00005−0.0002% (½–2 ppm.) and carbimazole at 0.0001−0.001% (1–10 ppm.) in low iodine feed could be detected as shown by reduced I131 uptake in comparison with controls.

Antithyroid effects of aminotriazole.

Aminotriazole, Like other antithyroid compounds and low-iodine diets, produces adenomatous changes in the thyroid glands of rats when fed continuously for long periods. Such changes are reversible if the antithyroid regime is discontinued. The antithyroid compounds that are naturally present in food are not regarded as causes of cancer.

Response of the thyroidal iodide pump and thyroid weight to goitrogens in rats fed low or high iodine diets.

Rats fed a diet rich in iodine and killed in groups 1–23 days after the initiation of goitrogenic regimens (methylmercaptoimidazole in the drinking water or propylthiouracil injected subcutaneously) showed a prompt and progressive rise in the thyroid-serum radioiodide concentration ratio (T/S) and the thyroidal radioiodide space; goiter developed more slowly. In rats on a low iodine diet treated with the same goitrogens the initially high T/S was significantly diminished during the first week of antithyroid treatment and even the thyroidal radioiodide space showed transient contraction; the goitrogenic effect of propylthiouracil manifested itself earlier than in the rats on the high iodine diet. No significant depression of the. T/S was achieved when rats fed the low iodine regimen were injected with thyrotrophin; thyroidal radioiodide space and thyroid size increased. The same dose of hormone given to rats on the high iodine diet markedly raised the T/S and expanded the thyroidal radioiodide space, but it had only a statistically equivocal effect on thyroid weight. Hypophysectomized rats maintained on the low iodine diet and injected with thyrotrophin showed high T/S values which were further enhanced by short term treatment with propylthiouracil; the size of the thyroids was not affected by the goitrogen and their radioiodide space therefore increased to the same extent as the T/S. The paradoxical effect of goitrogens on the thyroidal iodide pump of iodine deficient intact rats is discussed.

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Effect of goitrogens on adrenal gland of the rat

Seven goitrogens were studied to determine whether adrenal atrophy was a characteristic response to administration of antithyroidal agents. Treatments consisted of administration of thiouracil (0.1%), Tapazole (Lilly, 0.001%, 0.005% and 0.01%) and potassium perchlorate (1%) in drinking water and feeding of low iodine diet, p-aminosalicylic acid (PAS, 1%, 2%, 4%), p-aminobenzoic acid (PABA, 2%, 4%) and sulfaguanidine (2%, 4%) in the diet. After 12 weeks of treatment, the animals were anesthetized with sodium pentobarbital, blood was withdrawn by cardiac puncture for steroid analyses and the weights of the pituitary, thyroid, adrenal and thymus glands were determined. Treatment with thiouracil, Tapazole, perchlorate, PABA and sulfaguanidine induced an atrophy of the adrenal gland. Administration of PAS and the low iodine diet brought about hypertrophy of the thyroid gland without adrenal atrophy. Feeding with PABA, at the level of 2% in the diet, induced adrenal atrophy without thyroid hypertrophy while at the 4% level both thyroid hypertrophy and adrenal atrophy occurred. PABA at both dose levels brought about a shift in plasm corticoid levels. Plasmaa from rats given PABA was found to contain little or no corticosterone while the concentration of 17-hydroxycorticoids was markedly increased.

Effect of frequent housing changes and of muscular exercise on the thyroid gland of mice.

The possibility that the psychological stimulation resulting from frequent changes ofhousing might have an effect on the thyroid was investigated in mice “transferred” daily to different types of cages for a period of 8 weeks. Similarly, the effect of forced muscular exercise was investigated in mice made to walk daily 3 ½ to 4 hours in a rotating cage for a period of 8 weeks.All animals were fed controlled diets with low or adequate levels of dietary iodine. Control mice on the low iodine diet had enlarged thyroids showing histological signs of stimulation. “Transferred” or exercised mice fed the same diet failed to show thyroid stimulation. Thus, frequent housing changes and forced muscular exercise prevented the thyroid stimulation resulting from iodine deficiency. This depressing effect on the thyroid does not appear to be due to unspecific stress, since adrenal weight was not altered.

MECHANISM OF ANTITHYROID EFFECTS OF A SULFONYLUREA IN THE RAT1

In studies designed to elucidate the mechanism of antithyroid effects of carbutamide an hypoglycemic sulfonylurea, rats were fed a synthetic low iodine diet with carbutamide, sulfaguanidine, propylthiouracil and iodide added in various concentrations. Carbutamide (0.125 to 1.0%) reduced I131 uptake, increased thyroid weight and depleted glandular iodine. It was found to be 13 times as potent as sulfaguanidineand 1/200th of propylthiouracil. In contrast to sulfaguanidine and like propylthiouracil the goiters produced by carbutamide were inhibited by excess iodide. In rats fed carbutamide, I131 accumulated inthe thyroid but was promptly discharged by thiocyanate. Except for a delay of 3 days in maximum activity the antithyroid effects of carbutamide were indistinguishable from propylthiouracil.

Effects of methyl testosterone on thyroid function, thyrozine metabolism, and thyroxine-binding protein.

Studies on the effect of androgenic steroids on thyroid function are difficult to evaluate because of a number of apparent discrepancies. Money, Kirschner, Kraintz, Merrill, and Rawson (1), using castrate rats on a low iodine diet, found that testosterone propionate had no influence on thyroid weight or on thyroid weight: body weight ratio, but did increase the radioiodine uptake. Kochakian and Evans (2) recently reported that this form of testosterone failed to influence the uptake or release of radioiodine by the thyroid of the castrate rat. Burris, Bogart, and Krueger (3), using heifers and young steers, found that testosterone propionate produced an increased gain in weight; furthermore, the thyroids of the treated animals weighed more, contained less colloid, and exhibited an increase in thyroid cell height. Voitkevich (4) is cited as stating that the goiters produced by propylthiouracil in guinea pigs and cocks are very considerably decreased by simultaneously administered methyl testosterone, and that propylthiouracil goiters are larger in castrate than -in normal cocks.