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The effects of antithyroid drugs on intercellular mediators.

The antithyroid drugs methimazole and propylthiouracil have been shown to affect the function of monocytes and B and T lymphocytes in vitro. The aim of this study was to investigate the mechanism responsible for signalling between these various cell types. Propranolol, a drug known to have no effect on the immune system, was also included as a control against which the effects of the other drugs could be monitored. Peripheral blood lymphocytes from control subjects were stimulated with phytohemagglutinin in the presence or absence of antithyroid drugs. Propranolol was found significantly to inhibit beta 2 microglobulin production. In addition it was also found to be a very weak scavenger of free oxygen radicals. Methimazole significantly increased interleukin 2 levels (p less than 0.01), but had no significant effect on either gamma-interferon or beta 2 microglobulin production. Propylthiouracil also increased interleukin 2 levels (p less than 0.001) and significantly decreased beta 2 microglobulin production (p less than 0.01). Both drugs were found to be scavengers of free O2 radicals. It would appear that IL-2 is involved in intercellular signalling and this process may involve free radicals.

Cell Communication↗

Thyrotropin-dependence of the distribution of peroxidase in rat thyroid gland.

After male rats were injected daily with propylthiouracil, whale thyrotropin, or thyroxine for several days, the thyroid glands were examined for their ultrastructural localization of peroxidase. The propylthiouracil treatment caused a marked increase in the number of round, peroxidase-positive vesicles in the apical and middle regions of cytoplasm, and brought about a formation of granular reaction products in the colloid lumen adjacent to the elongated microvilli. Such changes became evident after 2 days of the drug treatment and increased with the time of the effect, until the whole colloid lumen was filled with the reaction products and very elongated microvilli. The effect of exogenous thyrotropin was essentially similar, to a lesser degree, to the drug effect mentioned above. The thyroxine treatment diminished the population of the small vesicles, as usually seen in the case of normal rat thyroids. When the thyroids of thyrotropin-stimulated and unstimulated rats were homogenized and fractionated into particulates fractions and a soluble fraction, almost all the peroxidase activity was contained in the former in both cases. Based on these results, the dynamics and the physiological role of the intracellular peroxidase are discussed.

Animals↗

Measurement of thyroid hormone in experimental thyroid tumours in rats.

Rats treated with 131I and propylthiouracil were shown to develop thyroid tumours 7--9 months after treatment. In this group, the levels of total thyroxine and tri-iodothyronine, and free thyroxine and tri-iodothyronine in the serum were low, and that of TSH was raised. In a group of rats treated with 131I and then propylthiouracil and thyroxine, thyroid tumours were found despite normal concentrations of total and free thyroxine and tri-iodothyronine in the serum. The level of TSH in the serum was significantly raised in this group. Thyroid tumours were not found in the various control groups of rats.

Animals↗

Influence of sodium perchlorate on thiourylene antithyroid drug accumulation in mice.

Radiolabelled [35S]propylthiouracil and [35S]methimazole were shown to accumulate in mouse thyroid gland in vivo, with maximal tissue/plasma ratios and maximal intrathyroidal levels of 35S-labelled drug being seen at the lowest dose of drug studied (0.1 micrograms/animal). Pretreatment with sodium perchlorate (10 mg) abolished iodide trapping by the thyroid and caused a fall in accumulation of both [35S]methimazole and [35S]propylthiouracil, although this effect was not seen at higher doses of drug, when tissue/plasma ratios approached unity. These data suggest that thiourylene antithyroid drug accumulation by the thyroid gland does not depend directly on the anion trap, and it is suggested that this accumulation might depend on subsequent intrathyroidal drug metabolism.

Animals↗

Autoimmune hepatitis associated with Graves' disease.

A 31-year-old woman with Graves' disease with a 12-month-history of propylthiouracil intake and autoantibodies in the sera was admitted to our hospital. The differential diagnosis between autoimmune hepatitis and propylthiouracil-induced hepatitis was intractable. Steroid therapy was started and she showed a complete response to the treatment. Liver biopsy demonstrated acute hepatitis and plasma cell infiltration. A second liver biopsy, which was performed 10 months after starting steroid therapy, showed some inflammatory cells in the portal tracts. These findings suggest that she had been suffering from autoimmune hepatitis.

Adult↗

Graves' disease accompanied by anti-myeloperoxidase antibody-related nephropathy and autoimmune hepatitis.

A 17-year-old woman was admitted because of proteinuria, microhematuria and liver dysfunction with increased antinuclear antibody and anti-myeloperoxidase antibody (MPO-ANCA). Fourteen months' previously, urinalysis and liver function showed normal range. At that time she suffered from tachycardia and weight reduction, diagnosed as Graves' disease, she was given propylthiouracil for treatment of her Graves' disease. The histological finding of renal biopsy was compatible with minor glomerular abnormalities. Liver biopsy finding was compatible with autoimmune hepatitis. After we had administered prednisolone, liver function returned to normal range and urine protein became negative. Then we performed subtotal thyroidectomy, and she was not given propylthiouracil. MPO-ANCA decreased gradually.

Adolescent↗

Effects of thyrotropin and thyroid hormones in vivo on thyroid responsiveness to thyrotropin in vitro.

The thyroid gland of rats fed propylthiouracil is known to be unresponsive in vitro to thyrotropin; to investigate further the underlying mechanism groups of rats were variously treated with propylthiouracil and thyroid hormone or subjected to hypophysectomy. In vitro responsiveness of the thyroids was tested by measuring an increase in the concentration of c AMP when thyrotropin or prostaglandin E1 was added to the medium. Results showed that responsiveness to thyrotropin partially returned with rats fed prophylthiouracil and hypophysectomized 5, but not 2, days before death; hypophysectomy of normal rats led to increased in vitro responsiveness to thyrotropin and this was partially reversed by injections of thyrotropin for a week before death. Administration of thyroid hormone had little effect in these investigations and in vitro responsiveness to prostaglanding E1 was not consistently influenced by any of the in vivo regimens. From this experience we conclude that, at least as studied in vitro, circulating thyrotropin has a significant role in modulating responsiveness of the thyroid to thyrotropin.

3',5'-Cyclic-AMP Phosphodiesterases↗

Vasoactive intestinal peptide enhances thyroidal iodide uptake during dietary iodine deficiency.

The presence of vasoactive intestinal peptide and neuropeptide Y in thyroid nerves and their effects on thyroid blood flow are well known. However, the effects of these two neuropeptides on the various processes involved in thyroid hormone biosynthesis and release have not been fully explored. We have now tested these two peptides for effects on an early step in thyroid hormone biosynthesis, namely iodide uptake, a process which is comprised of trapping and organification. In these experiments, we have used anesthetized adult male rats pretreated with thyroxine or fed a low iodine diet to increase thyroidal sensitivity. Vasoactive intestinal peptide significantly increased iodide uptake in rats fed an iodine deficient diet but not in those fed a normal iodine diet. This effect disappeared if animals were pretreated with propylthiouracil. Neuropeptide Y did not alter iodide uptake in rats on either the low or the high iodine diet, regardless of the presence or absence of propylthiouracil. The effect of vasoactive intestinal peptide on iodide uptake could be due to its influence on the organification of iodine, or on thyroid blood flow, or on both processes.

Analysis of Variance↗

Antithyroid drugs ameliorate thymectomy-induced experimental autoimmune thyroiditis.

The possible immunosuppressive action of antithyroid drugs in vivo has been assessed using Buffalo (Buf) strain rats with thyroiditis produced by neonatal thymectomy; this model shares many features with spontaneous thyroiditis in man. Both propylthiouracil and methimazole significantly reduced the severity of thyroiditis (P less than 0.01 compared to controls), irrespective of effects on thyroid status. Thyroidal Ox 8 (suppressor/cytotoxic) and W3/25 (helper) T-cells were reduced in number equally in treated animals, and thyroid follicular cell Ia expression was absent in a high proportion of these glands. Neither agent alone altered circulating antithyroglobulin antibody levels but there was a significant fall in antibody levels in animals treated with propylthiouracil and thyroxine. Antithyroid drugs had no effect on circulating T-cell subsets, and there was no direct suppressive action in vitro on Ia expression by the FRTL5 thyroid cell line. These results provide further support for a direct action of antithyroid drugs on autoimmune process in thyroid disease exerted in particular on the thyroid lymphocytic infiltrate.

Animals↗

Effects of antithyroid drug on the rectal temperature and metabolic parameters of ducks (Cairina moschata).

The effect of propylthiouracil oral treatment (400 mg/day per bird for 20 days) on body and thyroid weight, rectal temperature and plasma metabolic parameters of ducks (Cairina moschata) was determined. Propylthiouracil treatment produced a reduction (P less than .01) in body weight and an increase (P less than .01) in thyroid weight. The antithyroid drug also produced a decrease in rectal temperature starting from the 15th day of treatment, but did not significantly change blood glucose. Plasma free fatty acids and cholesterol concentrations progressively increased from the 5th and 10th day, respectively, in treated animals.

Animals↗

Agranulocytosis associated with antithyroid drugs. Effects of patient age and drug dose.

The records of all patients with antithyroid drug-related agranulocytosis at two Boston hospitals (Group 1, 14 patients), as well as the published case reports of 36 patients with this syndrome (Group 2) were reviewed. The clinical characteristics of these patients were then compared with those of 50 hyperthyroid patients who had taken antithyroid medication without untoward hematologic reactions (Group 3). The mean ages of patients in Group 1 and Group 2 were significantly greater than that of Group 3 (50.6 +/- 16 years versus 35.7 +/- 13.7 years, p less than 0.001; 46.3 +/- 18.7 years versus 35.7 +/-- 13.7 years, p less than 0.02). By chi-square analysis, the relative risk of developing agranulocytosis in patients over age 40 was 6.4 times that among younger patients (p less than 0.001). The mean doses of methimazole in Group 1 and Group 2 were significantly higher than that in Group 3 (43.8 +/- 9.9 mg/d versus 29.5 +/- 10.4 mg/d, p less than 0.001; 40.7 +/- 15.7 mg/d versus 29.5 +/- 10.4 mg/d, p less than 0.02), with and 8.6-fold increased risk of agranulocytosis with doses greater than 40 mg/d (p less than 0.01). In contrast, the mean doses of propylthiouracil did not differ among the three groups. These data suggest that antithyroid drugs should be administered cautiously to patients over age 40. Because no cases of agranulocytosis were seen with methimazole doses less than 30 mg/d, low-dose methimazole therapy may be safer than high-dose therapy or treatment with conventional doses of propylthiouracil.

Adolescent↗

[Antithyroid agents and embryopathies].

First cause of hyperthyroidism among women of childbearing age, Graves' disease raises the risk of maternal and fetal complications, including eclampsia, cardiac failure, abortion, prematurity, fetal death, all of which can be avoided if maternal hyperthyroidism is closely controlled. The risk of transplacental hyperthyroidism has been shown to correlate to the titre of anti-TSH receptor antibodies and has to be evaluated not only in women treated for Graves' disease during pregnancy, but also in women who have previously received radio iodine treatment or undergone surgery for Graves' disease: TSH-receptor antibodies may indeed remain at a high level several years after initial treatment. Both methimazole and propylthiouracil are equally effective to restore maternal euthyroidism. Accumulation of case-reports relating congenital malformations (mostly aplasia cutis, but in some cases, severe malformations) among the offspring of methimazole-treated women suggests the possibility of a teratogenic effect of methimazole. Despite the fact that the link between severe congenital defects and methimazole exposure during pregnancy is not formally established, propylthiouracil should be preferred to methimazole for the treatment of young hyperthyroid women.

Abnormalities, Drug-Induced↗

Cyclic nucleotide phosphodiesterases and thyroid hormones.

Evidence is presented that modulation of the maximum velocity of a particulate low K-m cyclic adenosine 3':5'-monophosphate (cyclic AMP) phosphodiesterase by thyroid hormones is one mechanism for the regulation of the responsiveness of rat epididymal adipocytes to lipolytic agents such as epinephrine and glucagon. Fat cells of propylthiouracil-induced hypothyroid rats are unresponsive to lipolytic agents and the V-max of particulate low K-m cyclic AMP phosphodiesterase of these cells is elevated above normal. In vivo treatment of hypothyroid rats with triiodothyronine restores to control values both the lipolytic response of the fat cells to epinephrine and the V-max of the particulate bound low K-m cyclic AMP phosphodiesterase. No similar correlation is found with the soluble high K-m cyclic AMP phosphodiesterase. The phosphodiesterases of fat cells from normal and hypothyroid rats respond identically in vitro to propylthiouracil, triiodothyronine, methylisobutylxanthine, or theophylline, although the particulate low K-m cyclic AMP phosphodiesterase is inhibited to a greater extent than soluble cyclic guanosine 3':5'-monophosphate phosphodiesterase activity. Protein kinase of fat cells from hypothyroid rats can be stimulated by cyclic AMP to the same total activity as observed in fat cells of normal rats. However, less of the protein kinase in fat cells from hypothyroid rats was in the cyclic AMP-independent form. This shift in the equilibrium of protein kinase forms is consistent with an increased activity of low K-m cyclic AMP phosphodiesterase and probably results from a lowering of the lipolytically significant pool of cyclic AMP.

Adipose Tissue↗

Unusual complications of antithyroid drug therapy: four case reports and review of literature.

Two cases of propylthiouracil-associated acute hepatitis, one case of fatal methimazole-associated hepatocellular necrosis and one case of propylthiouracil-associated lupus-like syndrome are described. The literature related to antithyroid drug side effects and the mechanisms for their occurrence are reviewed and the efficacy and complications of thyroidectomy and radioiodine compared to those of antithyroid drugs. It is concluded that in most circumstances 131I is the therapy of choice for hyperthyroidism.

Adult↗

Adverse immunologic effects of antithyroid drugs.

Propylthiouracil and methimazole are frequently used in the management of hyperthyroidism. Two patients in whom adverse immunologic effects other than isolated agranulocytosis developed during treatment with propylthiouracil are described. A review of the literature revealed 53 similar cases over a 35-year period. Rash, fever, arthralgias and granulocytopenia were the most common manifestations. Vasculitis, particularly with cutaneous manifestations, occurs and may be fatal. The clinical evidence suggests that an immunologic mechanism is involved. A number of different autoantibodies were reported, but antinuclear antibodies were infrequent, and none of the cases met the criteria for a diagnosis of systemic lupus erythematosus. Thus, the reactions do not represent a true drug-induced lupus syndrome. Current hypotheses and experimental data regarding the cause of the reactions are reviewed. No specific clinical subgroup at high risk can be identified, and manifestations may occur at any dosage and at any time during therapy. Cross-reactivity between the two antithyroid drugs can be expected. Except for minor symptoms (e.g., mild arthralgias or transient rash), such reactions are an indication for withdrawal of the drug and the use of alternative methods to control the hyperthyroidism. In rare cases of severe vasculitis a short course of high-dose glucocorticoid therapy may be helpful.

Adult↗

Serum concentrations of thyroxine, 3,5,3'-triiodothyronine, thyrotropin, and prolactin in dogs before and after thyrotropin-releasing hormone administration.

Serum concentrations of thyrotropin (TSH), prolactin, thyroxine, and 3,5,3'-triiodothyronine in 15 euthyroid dogs and 5 thyroidectomized and propylthiouracil-treated dogs after thyrotropin-releasing hormone (TRH) administration were measured. Although thyroidectomized and propylthiouracil-treated dogs had higher (P less than 0.01) base-line concentrations of TSH in serum than did euthyroid dogs, concentrations of TSH after TRH administration varied at 7.5, 15, and 30 minutes with 14 of 45 samples obtained from healthy dogs having lower TSH concentrations than before TRH challenge. Similarly, concentrations of 3,5,3'-triiodothyronine in the serum of euthyroid dogs 4 hours after TRH administration were similar (P less than 0.05) to concentrations before TRH challenge. Although the mean concentration of thyroxine in serum was elevated (P less than 0.05) 4 hours after administration of TRH to euthyroid animals, as compared with base-line levels, the individual response was variable with concentrations not changing or decreasing in 4 dogs. Therefore, the TRH challenge test as performed in the current investigation was of limited value in evaluating canine pituitary gland function. Although mean concentrations of TSH in serum were higher (P less than 0.05) in euthyroid dogs after TRH administration, the response was too variable among individual animals for accurate evaluation of pituitary gland function. Concentrations of prolactin in the sera of dogs after TRH administration, confirmed previous reports that exogenously administered TRH results in prolactin release from the canine pituitary and indicated that the TRH used was biologically potent.

Animals↗

Prenatal treatment of thyrotoxicosis to prevent intrauterine growth retardation.

A woman with hypothyroidism and Graves ophthalmopathy was treated with propylthiouracil during her second pregnancy. This was employed because her first pregnancy resulted in an infant with severe intrauterine growth retardation and neonatal thyrotoxicosis. The antithyroid drug used during the second pregnancy crossed the placenta and treated the infant in utero. The infant was delivered by elective cesarean section at 36 weeks and was a live-born male with appropriate height and weight without evidence of thyrotoxicosis. The therapeutic benefit of propylthiouracil during this second pregnancy seems likely, based on the development of neonatal thyrotoxicosis after 4 days of life and on the presence of high thyroid-stimulating immunoglobulin levels in the mother and the infant.

Adult↗

Thyroid status alters structure of VLDL secreted by perfused rat liver.

The interaction of thyroid status and oleic acid infusion rate on the thermal behavior of the very low density lipoprotein (VLDL) secreted by isolated perfused rat liver was examined. The livers were infused at 37 degrees C with oleate at rates of 0, 83, 166, or 332 mumoles/hr for 4 hours and VLDL was isolated from the perfusate at 12 degrees C. The lipid composition of the VLDL secreted by the perfused liver from hyperthyroid animals was dramatically different from controls at all infusion rates of oleate. Significant changes in the ratio of [phospholipid + cholesterol]/[triglyceride] and in fatty composition of secreted triglycerides occurred. Differential scanning calorimetry of the intact VLDL and extracted triglycerides secreted by euthyroid rats suggested the existence of four thermotropic endothermic transitions centered at -20.5, -14.0, -3.0, and 9.0 degrees C. Both the total enthalpies and the temperatures at which the phase alterations occurred in the triglyceride fraction from VLDL secreted by livers from euthyroid rats were highly dependent on the rate of infusion of oleate. Pretreatment of the rats with triiodothyronine and infusion of 332 mumoles oleate/hr abolished in the intact VLDL the temperature transitions centered at -20.8 and at 10.5 degrees C and decreased the total enthalpy from 8.13 to 38.5 cal/gm. Livers from rats pretreated with propylthiouracil and infused with oleate at 332 mumoles/hr secreted VLDL in which only one transition centered at -5.0 degrees C remained. The total enthalpy was unaffected. At all rates of infusion of oleate, the phase behavior of the intact VLDL or triglycerides extracted from the VLDL was altered by prior treatment of the rats with triiodothyronine or propylthiouracil. The thyroid state of the rat profoundly affected the thermal properties of the VLDL secreted by the perfused liver infused with the unsaturated fatty acid oleate.

Animals↗