Antioxidant effects of α-lipoic acid against epididymal oxidative damage in adult offspring rats exposed to maternal hypothyroidism stress

It is well known that the epididymis promotes post-testicular sperm maturation events. However, its malfunction during congenital hypothyroidism is relatively less understood as compared to the testis. The present study evaluated the probable effect of α-lipoic acid on epididymal oxidative stress parameters in rats exposed to antithyroid drug, carbimazole during fetal period. Time-mated pregnant rats in unexposed and carbimazole (1.35 mg/Kg body weight exposed were allowed to deliver pups and weaned. At postnatal day 100, the F1 male pups were assessed for epididymal endpoints. Among the epididymal regions, significant elevation of lipid peroxidation levels, superoxide anion, and hydrogen peroxide contents with a concomitant reduction in the activity levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and reduced glutathione levels were observed in cauda epididymis of carbimazole exposed rats over controls. Significant elevation in sperm DNA fragmentation (comet assay), accelerated cauda epididymal sperm transit time and reduction in epididymal sialic acid content was observed in carbimazole exposed rats. RT-qPCR studies revealed that embryonic exposure to carbimazole resulted in down regulation of androgen receptor, nuclear factor eryrthoid 2 like 2, 5α-reducatse 1 mRNA levels, while up regulation of caspase 3 mRNA was observed in epididymal regions of rats. In addition, fetal exposure to carbimazole resulted in disorganization of cauda epididymal architecture in rats. Conversely, supplementation of α-lipoic acid (70 mg/Kg bodyweight) during PND 3 to 14 restored epididymal functions in carbimazole exposed rats and the ameliorative effects of lipoic acid could be attributed to its antioxidant and steroidogenic effects.

The protective impact of hesperidin against carbimazole-induced hypothyroidism, via enhancement of inflammatory cytokines, histopathological alterations, and Nrf2/HO-1

The aim of this study was to evaluate the anti-inflammatory, antioxidant, and antiproliferative effects of hesperidin (HSP) and eltroxin (ELT) on hypothyroidism (HPO) induced by carbimazole (CBZ) in white male albino rats. Thirty-two adult rats were categorized into four groups: Group 1, no treatment (control); Group II, treated with CBZ (20 mg/kg); Group III, treated with HSP (200 mg/kg) + CBZ; and Group IV, treated with ELT (0.045 mg/kg) + CBZ. All treatments were provided as oral daily doses for 90 days. Thyroid hypofunction was significantly manifested in Group II. However, increased levels of thyroid hormones, antioxidant enzymes, nuclear factor erythroid 2-related factor 2, heme oxygenase 1, and interleukin (IL)-10, and a decrease in the level of the thyroid-stimulating hormone were observed in Groups III and IV. On the contrary, decreased levels of lipid peroxidation, inducible nitric oxide synthase, tumor necrosis factor α, IL-17, and cyclooxygenase 2 were detected in groups III and IV. The histopathological and ultrastructural findings were ameliorated in Groups III and IV; on the contrary, Group II presented with significant increases in the height and number of layers of the follicular cells. Immunohistochemistry demonstrated a marked increase in thyroglobulin and significant decreases in the levels of nuclear factor kappa B and proliferating cell nuclear antigen in Groups III and IV. These results confirmed the effectiveness of HSP as an anti-inflammatory, antioxidant, and antiproliferative agent in rats with hypothyroidism. Additional studies are required to assess its potential as a novel agent against HPO.

Complexation of uranyl (UO2)2+ with bidentate ligands: XRD, spectroscopic, computational, and biological studies

Three new uranyl complexes [(UO₂)(OAc)₂(CMZ)], [(UO₂)(OAc)₂(MP)] and [(UO₂)(OAc)₂(SCZ)] were synthesized and characterized by elemental analysis, FT-IR, UV-Vis spectroscopy, powder XRD analysis, and molar conductivity. The IR analysis confirmed binding to the metal ion by the sulfur and ethoxy oxygen atoms in the carbimazole (CMZ) ligand, while in the 6-mercaptopurine (MP) ligand, the sulfur and the N7 nitrogen atom of a purine coordinated binding to the metal ion. The third ligand showed a 1:1 molar ratio and bound via sulfonamide oxygen and the nitrogen of the pyrimidine ring. Analysis of the synthesized complexes also showed that acetate groups had monodentate binding to the (UO₂²⁺). Density Functional Theory (DFT) calculations at the B3LYP level showed similar structures to the experimental results. Theoretical quantum parameters predicted the reactivity of the complexes in the order, [(UO₂)(OAc)₂(SCZ)] > [(UO₂)(OAc)₂(MP)]> [(UO₂)(OAc)₂(CMZ)]. DNA binding studies revealed that [(UO₂)(OAc)₂(SCZ)] and [(UO₂)(OAc)₂(CMZ)] have the highest binding constant (K_b) among the uranyl complexes. Additionally, strong binding of the MP and CMZ metal complexes to human serum albumin (HSA) were observed by both absorbance and fluorescence approaches. The antibacterial activity of the complexes was also evaluated against four bacterial strains: two gram-negative; Escherichia coli and Klebsiella pneumonia, and two gram-positive; Staphylococcus aureus and Streptococcus mutans. [(UO₂)(OAc)₂(MP)] had the greatest antibacterial activity against Klebsiella pneumonia, the gram-positive bacteria, with even higher activity than the standard antibiotic. In vitro cytotoxicity tests were also performed against three human cancer lines, and revealed the most cytotoxic complexes to be [(UO₂)(OAc)₂(SCZ)], which showed moderate activity against a colon cancer cell line. Thus, uranyl addition enhances the antibacterial and anticancer properties of the free ligands.

Pharmacodynamic Response to Anti-thyroid Drugs in Graves' Hyperthyroidism

Objective: Graves' disease is the commonest cause of hyperthyroidism in populations with sufficient dietary iodine intake. Anti-thyroid drugs (ATD) are often used as the initial treatment for Graves' hyperthyroidism, however there is a paucity of data relating the dose of ATD therapy to the effect on thyroid hormone levels, increasing the risk of both over- and under-treatment. We aimed to determine the pharmacodynamic response to the ATD carbimazole. Design: Retrospective cohort study. Methods: Participants were patients (n = 441) diagnosed with Graves' disease at Imperial College Healthcare NHS Trust between 2009 and 2018. The main outcome measure was change in thyroid hormone levels in response to ATD. Results: Baseline thyroid hormone levels were positively associated with TSH receptor antibody titres (P < 0.0001). Baseline free triiodothyronine (fT3) were linearly related to free thyroxine (fT4) levels in the hyperthyroid state (fT3 = fT4^*0.97-11), and fell proportionately with carbimazole. The percentage falls in fT4 and fT3 per day were associated with carbimazole dose (P < 0.0001). The magnitude of fall in thyroid hormones after the same dose of carbimazole was lower during follow up than at the initiation visit. The fall in thyroid hormone levels approximated to a linear response if assessed at least 3 weeks after commencement of carbimazole. Following withdrawal of antithyroid drug treatment, the risk of relapse was greater in patients with higher initial fT4, initial TSH receptor antibody titre, males, smokers, and British Caucasian ethnicity. Conclusion: We identify a dose-response relationship for fall in thyroid hormones in response to carbimazole to aid in the selection of dose for Graves' hyperthyroidism.

Testicular germ cell tumour presenting as thyrotoxicosis

A case is reported of a patient who presented to his family doctor with a short history of cough with signs and symptoms of thyrotoxicosis. Carbimazole treatment had little effect and his symptoms worsened to include severe shortness of breath. He was investigated further and found to have multiple lung and liver metastases from an unknown primary site. Biopsy and subsequent post-mortem investigations revealed a testicular tumour and a grossly elevated serum human chorionic gonadotrophin (hCG) concentration.

The biochemical and clinical thyrotoxicosis is presumed to be due to the thyrotrophic activity of excess hCG secretion, in a situation analogous to that seen in hydatidiform mole or in hyperemesis gravidarum.

Effect of L-thyroxine and carbimazole on blood levels of biogenic amines in rat

Circulating levels of 5-hydroxytryptamine (5HT), histamine, monoamine oxidase (MAO), histaminase, tri-iodothyronine (T3) and thyroxine (T4) were studied in L-thyroxine and carbimazole treated rats. Increased concentrations of 5-HT, histamine, glutamate, T3 and T4 were recorded in L-thyroxine-treated rats while plasma gamma-aminobutyric acid (GABA), MAO and histaminase levels were significantly decreased. Considerable reduction in 5-HT, glutamate, T3 and T4 with trend towards the rise in plasma levels of MAO and histaminase was noticed in carbimazole treated group. There was a significant correlation between these amines and thyroid hormone values. The findings suggest that alterations in the metabolism of thyroid hormones may have a link with the altered metabolism of biogenic amines.

The effects of long-term antithyroid drug treatment on serum reverse T3 in patients with Graves' disease

The effects of long-term treatment with antithyroid drugs, carbimazole (CMI) or propylthiouracil (PTU), on serum reverse triiodothyronine (rT3) levels were studied in 23 patients with Graves' disease. Nineteen patients were given CMI and four PTU for a minimum of six months. After one month of treatment the serum levels of thyroxine (T4), triiodothyronine (T3) and rT3 had normalized in both groups. When L-thyroxine was added to the regimens after two months of therapy, both serum T4 and rT3 levels increased, whereas serum T3 level continued to fall. The serum levels of rT3 seemed to be dependent on and followed the T4 levels so closely that determinations of rT3 in the medical management of patients with Graves' disease will be of little clinical use.

Iodide excess exerts oxidative stress in some target tissues of the thyroid hormones

Environmental iodine deficiency continues to be a significant public health problem worldwide. On the other hand, iodide excess results principally from the use of iodine-containing medicinal preparations or radiographic contrast media. For this reason we intended to explore iodide excess impairment on prooxidant/antioxidant balance of the thyroid gland, hepatic tissue and in blood and the effect of selenium administration on oxidative stress markers under the same circumstances. Experiments were performed for 10 days with white, male, Wistar rats, as follows: group 1: control-normal iodine supply group; 2: high iodine diet, group; 3: high iodine diet and selenium; group 4: high iodine diet and Carbimasole. Oxidative stress markers such as lipid peroxides were determined in thyroid gland, hepatic tissue and in blood. Measuring H+ donor ability of the sera and catalase activity in thyroid gland and in hepatic tissue assessed antioxidant defense. Iodide excess had prooxidant effects, leading to an increased lipid peroxides level and catalase activity in target tissues and in blood and to a decreased H+ donor ability of the sera. Selenium supplementation had opposite effects. Present data allow us to conclude that the alterations due to iodide excess in thyroid gland, hepatic tissue and in blood are mediated through oxidative stress.

Graves' disease and coexisting struma ovarii: struma expression of thyrotropin receptors and the presence of thyrotropin receptor stimulating antibodies

Struma ovarii is a rare cause of hyperthyroidism and particularly rare in patients with coexisting Graves' disease. We describe a 28-year-old female who presented with symptoms and signs of hyperthyroidism (free thyroxine [FT(4)] 39 pmol/L, thyrotropin [TSH] < 0.05 mU/L) and associated ophthalmopathy, consistent with Graves' disease. The patient relapsed twice: once after initial successful management with carbimazole and subsequently after subtotal thyroidectomy. Radioisotope scanning showed focal uptake bilaterally in the neck and believing this was the source of thyroid hormone excess, carbimazole was restarted. A left ovarian mass was found on ultrasound during the investigation of unrelated nephrotic syndrome resulting from focal segmental glomerulosclerosis. A 555-g struma ovarii was removed surgically. Hypothyroidism developed postoperatively (FT(4) 9.7 pmol/L, TSH 36 mU/L). Circulating TSH receptor stimulating antibodies were positive and immunohistochemical studies confirm the presence of TSH receptors on the struma ovarii. The demonstration of TSH receptors on the struma ovarii increases previous speculation that struma ovarii growth and function may be augmented by the circulating TSH receptor stimulating antibodies of Graves' disease.

Assessment of povidone-iodine disinfectant compatibility with antimicrobial incise drape and adhesion inhibition on the skin using a gas chromatography/mass spectrometry approach

According to orthopedists' reports, substitution of the original for a generic povidone-iodine (PVP-I) disinfectant could have led to some adhesion problems of antimicrobial incise drapes on the field of operation with the consequence of increasing the infection risk. Three methods have been used to assess the case: (a) a gas chromatography/mass spectrometry (GC-MS) approach quantifying methimazole formation from carbimazole, (b) in vitro adhesion experiments on a smooth glass plate surface and (c) the analysis of intrasurgical procedures. GC-MS results confirmed the higher potency of the original compared to the generic PVP-I. In vitro comparison of the adhesion on a PVP-I-pretreated glass surface showed no difference between the disinfectants and no significant destruction of the adhesive layer. However, due to different surgery preparation procedures, the remaining free skin surface granting sufficient adhesion differed if the intervening surgeon himself or his assistant prepared the field of operation. As a conclusion, the original PVP-I disinfectant is confirmed as the first-choice disinfectant for the field of operation. Adhesion problems were arising with new surgical staff and thus different preparation procedures. Exchanging PVP-I disinfectants cannot explain the adhesion problems of drapes and antimicrobial incise foils on the skin.

Effects of carbimazole on morphology of rat adrenals

OBJECTIVE

Study was conducted to investigate the effects of (i) carbimazole and (ii) simultaneous administration of thyroxine (thyroid hormone analogue) on the morphology of rat adrenals.

DESIGN

A prospective case-control study.

PLACE AND DURATION OF STUDY

Department of Anatomy,Basic Medical Sciences Institute (BMSI), JPMC, Karachi, during a period of six weeks.

METHODOLOGY

The study was conducted on albino rats originally obtained from Charles River Breeding Laboratories, Brooklyn, Massachusetts, USA, and were cross bred, housed and maintained on balanced diet in the Animal House of BMSI, JPMC, Karachi. Eighteen adult albino rats used in the experiment were divided into three groups, i.e. A, B and C, each comprising 6 animals as control, carbimazole-treated, and carbimazole plus thyroxine-treated animals respectively. At the end of six weeks treatment all the animals were sacrificed and their adrenal glands removed, fixed, sectioned and stained with H&E and Sudan black. The histology of adrenals, width of cortex and its zones, and number of cells in different zones of cortex was studied.

RESULTS

Carbimazole affects the morphology of adult rat adrenals by decreasing the total width of cortex and its zones especially the zona fasciculata with decrease in number of cells. It also showed the increase in fat contents on Sudan black staining.

CONCLUSION

Carbimazole causes shrinkage of the adrenal cortex.

Effect of hypothyroidism and thyroxin replacement on growth of long bones in prenatally treated albino rats

OBJECTIVE

To study the effect of induced hypothyroidism and thyroxin replacement on bone growth.

DESIGN

An animal study carried out on experimental Albino rats.

PLACE AND DURATION OF STUDY

The study was carried out in the Department of Anatomy, Basic Medical Sciences Institute (BMSI), Jinnah Postgraduate Medical Centre (JPMC), Karachi, from June 1999 to May 2002.

METHOD

Pregnant female Albino rats obtained from the animal house of Basic Medical Sciences Institute, JPMC, Karachi were treated with carbimazole and carbimazole plus thyroxin from 10th day of gestation till parturition. Another group of pregnant rats did not receive any treatment and acted as controls. Pups born to the treated as well as control animals were sacrificed on 10th postnatal day and fixed in formal saline. They were then processed through 95% ethanol and acetone, bulk stained with alizarin red and cleared in 4% KOH to reveal their bony and cartilaginous elements. The ulna and tibia of both sides were disarticulated from the treated and control animals and measured for intact bone length and diameter. The measurements of the three groups were then compared statistically.

RESULTS

The retardation in length observed at the end of experimental period in ulna was by 13.67% and in tibia by 27.84% in carbimazole treated group while in carbimazole plus thyroxin treated group the reduction in length of ulna was 5.08% and of tibia 3.91% when compared with their age matched controls.

CONCLUSION

Prenatal hypothyroidism has an adverse effect on bone growth and results in reduction of long bone length.

SIMS evidence that carbimazole enhances spatial heterogeneity of thyroid iodine storage and targeting in a woman with Graves' disease

Antithyroid drugs (ATD) are known to reduce 131I efficacy in thyrotoxicosis, though the underlying mechanism remains misunderstood. To study the impact of long term administration of carbimazole on both iodine stores (127I, secondary ion mass spectrometry microscopy) and targeting (125I, radioautography) at the intraglandular level in a woman who underwent surgery for Graves' disease. 125I distribution was dramatically heterogenous and large areas of the sample appeared poorly or no stained at all. This may correspond to flat follicles, hypofunctioning or ATD blocked ones and to the various histological changes related to the thyroiditis. SIMS counting showed huge variations of the interfollicular iodine stores (0 to 1.18 microg/mg) and lower mean values than those observed in nodular goiters. SIMS imaging depicted iodine free areas and others with preserved thyroglobulin synthesis, as assessed via 32S- mapping, but low to undetectable 127I, suggesting focal organification defects. Since ATD reduce iodine storage and uptake capabilities and enhance the iodine heterogeneity of interfollicular targeting, a related enhancement of the spatial 131I dose distribution is unavoidable. ATD may reduce 131I efficacy by variably reducing the number of follicles which can be actually or significantly targeted, e.g. irradiated (antirecruitement effect).

Lowering of plasma triiodothyronine level and sympathetic activity does not alter hypoalbuminaemia in rats fed on a diet of low protein concentration

Previous studies have described high plasma triiodothyronine (T3) concentrations and sympathetic activity in rats fed on low-protein diets. The present investigation examined how the nutritional status of rats fed on a low-protein diet was affected when these hormonal changes were reduced by drug administration. The low-protein diet (LP group) prevented growth, reduced plasma albumin levels, elevated plasma T3 concentration, and increased both the weight of the interscapular brown adipose tissue (BAT) and the activity of BAT cytochrome c oxidase (EC 1.9.3.1). Lowering the plasma T3 concentration (with carbimazole; CA group) elevated the plasma insulin concentration, promoted a small increase in the plasma albumin concentration and caused weight gain in comparison with the LP group. Reduction of sympathetic activity (with alpha-methyl-p-tyrosine; MT group) promoted a small elevation in plasma albumin concentration accompanied by a diminished T3 concentration, BAT weight, and an increase in fat deposition in relation to LP rats. In a second experiment, simultaneous lowering of the plasma T3 concentration and sympathetic activity (CA/MT group) resulted in weight gain associated with elevated plasma insulin concentration and fat deposition and a marked reduction in BAT cytochrome c oxidase activity. However no change in the hypoalbuminaemia was observed. The results of the present study suggest that in spite of the previously described increase in metabolic rate in fed on a diet with low-protein concentration when compared with controls, the mechanisms involved in the control of BAT activity and fat deposition seem to be independent of those which cause liver protein depletion and hypoalbuminaemia.

Comparison of Kodak Amerlite FT4 and TSH-30 with T4 and TSH as first-line thyroid function tests

OBJECTIVES

To evaluate the effect of test automation and a change in strategy for thyroid function tests (TFT) on personnel needs and turn-around time. The first-line TFT were changed from T4 and TSH to FT4 and TSH-30.

DESIGN AND METHODS

Samples received for TFT from 357 randomly selected patients were analyzed by RIA for T4, and by IRMA for TSH as first-line tests. FT3 and TBG were requested as back-up tests when indicated. Patients were classified on the basis of these results and the clinical information received. All the samples were reanalyzed for FT4 and TSH on the Amerlite Processing Center, which is a batch, semiautomated immunoassay system. The thyroid status of the patients was compared using the two protocols and available clinical data.

RESULTS

There was good correlation between TSH-IRMA and TSH-30 in the 160 patients classified as euthyroid (r = 0.956; p < 0.001) and no euthyroid patient was reclassified with the new strategy. In 21 patients with borderline raised TSH-IRMA, FT4 was found to be low in only 2. All 11 patients classified as hypothyroid had TSH results greater than 10 mU/L and all except 2 patients had FT4 less than 11 nmol/L. The status of 21 hyperthyroid as well as 40 patients on carbimazole could be determined biochemically on the basis of agreement between both the FT4 and TSH-30 results. FT3 was only required if the FT4 and TSH-30 results were not in agreement. In 42 patients on T4 therapy, adequacy of replacement was assessed better using FT4 and TSH-30. No patient required backup testing with TBG to determine thyroid status using the new testing protocol. The change in TFT protocol reduced the 95% turn-around time from 3 days to 1 day.

CONCLUSION

The introduction of FT4 and TSH-30 as first-line TFT improved the turn-around time for TFT, resulted in 25% reduction in personnel requirements, 60% reduction in FT3 assays, and discontinuation of TBG assay.

[The effect of carbimazole on lactate dehydrogenase isoenzymes and thyroid hormone levels in sheep]

The oxidative processes in the organism are activated by hormones of the thyroid gland. The pyruvate-lactate component catalyzed by lactate dehydrogenase presents one of the important oxidic-reductive systems in the animal organism of biochemical importance (EC. 1.1.1.27). In certain cases of the thyroid gland disturbances antithyroid drugs, such as derivatives of thiouracil, mercaptoimidazole and some others may be used for the treatment of men and animals (Marchant et al., 1979; Negwer, 1987). In the present study, the activity changes of lactate dehydrogenase isoenzymes in the blood plasma of young rams and ewe hoggets in experiments with carbimasole [carbimasolum(1-carbaethoxy-3-methyl-2-thioimidazolum) ] have been studied. The dose of carbimasole at the time of sampling (May, 1993) was 7O mg per animals and day. In May, no significant differences in T3 and T4 concentrations in the serum of experimental and control animals in males and females were found (Tab. 1). The T3 concentrations in the experimental group of young rams were 0.56 +/- 0.21 nmol/l (n = 3), in ewe hoggets 0.70 +/- 0.19 nmol/l (n = 6). The T4 concentrations in young rams were 39.15 +/- 24.15 nmol/l (n = 3), in ewe hoggets 48.6 +/- 15.3 nmol/l (n = 6). Out of lactate dehydrogenase isoenzymes, only LD4 exhibited significant differences (P < 0.02) in the blood plasma of ewe hoggets (Tab. I). In the course of these months, no clinical signs of hypothyrosis were observed in experimental animals.

An increase in the blood thyroxine level after methylene blue in rats: the interaction with carbimazole

Anterior pituitary (AP) weight, thyroid weight, the serum thyroxine (T4) level, the thyroid T4 and cAMP content, the serum TSH level and the TSH and cAMP content of the AP and thyroid were measured in control rats, rats given methylene blue (MB) in their food, rats given the thyroid-blocking agent carbimazole (CARB) and rats fed both MB and CARB. AP weight fell slightly after MB in both intact and CARB--fed animals. Thyroid weight rose strongly after CARB, MB partly inhibited this increase. The cAMP content of the thyroid rose after CARB; this increase was likewise blocked by MB, MB alone had no effect on the thyroid cAMP concentration. Previous observations showing that MB produced an increase in the blood T, were confirmed. The T4 level fell, of course, after CARB and the decrease was partly inhibited by MB. The T4 content of the thyroid also fell after CARB, this decrease was completely reversed by MB. The blood TSH level fell slightly after MB and rose 7--fold after a CARB blockade of the thyroid; this increase was completely inhibited by MB. The TSH content of the AP fell after MB in both intact and CARB--fed animals. The cAMP content of the AP fell after MB, it was unaffected by CARB. Thus, in some way, MB raised the blood thyroxine level in both intact and CARB--fed animals and strongly depressed the TSH content in the serum and the AP given alone or with CARB. The mechanism of this action should be a result of MB interaction in thyroid hormone metabolism and their binding activity on specific regulatory elements. It is a problem for future experiments.

The effect of thyroxine or carbimazole treatment on gentamicin nephrotoxicity in rats

1. This study examines the effect of treating rats with gentamicin (80 mg kg-1 day-1 intramuscularly (i.m.), for 6 days) alone or with either L-thyroxine or the anti-thyroid drug carbimazole. 2. Gentamicin produced significant increases in serum creatinine and urea concentrations, and significantly reduced the activity of Na+,K+ATPase in renal cortex. The concentration of serum triiodothyronine (T3) was unaffected by graded doses (20, 40 and 80 mg kg-1) of the antibiotic. Histopathologically, gentamicin produced necrosis of proximal tubules in the renal cortical tissues of treated rats. 3. Treatment of rats with either L-thyroxine or carbimazole alone did not significantly affect any of the biochemical variables investigated. Carbimazole alone produced only mild tubular necrosis. 4. Treatment of rats with either L-thyroxine (100 micrograms kg-1 day-1, subcutaneously) for 10 days, and gentamicin (80 mg kg-1, i.m. daily during the last 6 days of treatment significantly reduced the gentamicin-induced increases in serum creatinine and urea concentrations, and increased the activity of cortical N+,K+ATPase to control levels. Histopathologically, the severity of gentamicin-induced tubular necrosis was reduced by L-thyroxine treatment. 5. Carbimazole (12 mg ml-1 in drinking water for 21 days) and gentamicin (80 mg kg-1 i.m.) daily during the last 6 days of treatment, stimulated the increase in serum urea concentration produced by gentamicin, but did not significantly affect the gentamicin-induced changes in serum creatinine or cortical N+,K+ATPase.

Effect of L-thyroxine and carbimazole on brain biogenic amines and amino acids in rats

Effect of L-thyroxine and carbimazole on brain biogenic amines and amino acids content and circulating levels of thyroid hormones has been investigated in rats. L-thyroxine treatment caused marked elevation of 5-HT, histamine and glutamate along with the decline in the level of GABA whereas administration of carbimazole had a contrary effect on rat hypothalamus. Further, L-thyroxine administration also raised histamine as well as glutamate content and decreased GABA level in thalamic region of the rat brain but carbimazole treatment reduced 5-HT and glutamate content in this area of the rat brain. Similarly, cortical content of 5-HT and histamine also increased following L-thyroxine administration whereas carbimazole treatment lowered 5-HT, histamine and glutamate levels. Simultaneously, there was a considerable rise in the circulating levels of T3 and T4 in L-thyroxine-treated rats and a marked reduction in their levels in carbimazole-treated rats. There is a positive correlation between these amines and the thyroid hormone level. Thus, the results suggest that L-thyroxine and carbimazole administration cause marked alteration in biogenic amines and amino acids in rat brain, which may have an important role in the functioning of thyroid gland.

Copper and cobalt complexes of carnosine and anserine: production of active oxygen species and its enhancement by 2-mercaptoimidazoles

Phosphate buffer solutions of two dipeptides prevalent in striated muscle, L-carnosine (beta-alanyl-L-histidine) and L-anserine (beta-alanyl-L-1-methylhistidine), produce active oxygen species as measured by bleaching of N,N-dimethyl-4-nitrosoaniline (RNO). Activity is enhanced 5-14-fold in the presence of 2-mercaptoimidazoles such as ergothioneine, carbimazole (3-methyl-2-mercaptoimidazole-1-carboxylate), methimazole (2-mercapto-1-methylimidazole) and 2-mercaptoimidazole but only slightly by thiourea and dimethylthiourea. Activity is proportional to carnosine concentration and to mercaptoimidazole concentration at a fixed concentration of the second component. A variety of imidazoles closely related to carnosine and anserine are inactive, even after addition of transition metal ions. Activity is moderately increased above the pKa of the carnosine imidazole ring (pH 7.2, 7.5 and 8.0) versus below the pKa (pH 6.5 and 6.8). Activity is slightly increased by addition of copper or cobalt ions but not by addition of ferrous or ferric ions. Activity is decreased by Chelex 100 pretreatment of phosphate buffer and stimulated when copper or cobalt ions are added to the chelated buffer but there is no significant stimulation by ferric ions. Catalase eliminates most activity but superoxide dismutase has little effect. We propose that metal-carnosine and metal-anserine complexes produce superoxide and also serve as superoxide dismutases with resultant accumulation of hydrogen peroxide. An unidentified radical produced from hydrogen peroxide subsequently bleaches RNO. From the biological distributions of carnosine, anserine and ergothioneine, we infer that deleterious effects are probably minimal under normal physiological circumstances due to tissue and cellular compartmentalization and to sequestration of these compounds and transition metal ions.

Iopanoic acid as an adjunct to carbimazole in the management of hyperthyroidism

BACKGROUND

The thiourea drugs take a few weeks to control the symptoms of hyperthyroidism whilst iodine containing radiographic contrast agents (iopanoic acid and sodium ipodate) have a more rapid effect. There is no report on the use of iopanoic acid administered in conjunction with carbimazole, so we evaluated the efficacy of this combination in the early medical management of patients with hyperthyroidism.

METHODS

Thirty hyperthyroid patients diagnosed by clinical and biochemical criteria were randomized into two treatment groups. Group A (n = 16) received iopanoic acid (500 mg orally twice a day for the first 3 weeks) and carbimazole (30 mg orally in three divided doses) while group B (n = 14) received carbimazole alone. Clinical examination and estimation of serum total T3, total T4 and TSH were done by radioimmunoassay at the start of therapy, weekly for 4 weeks and then at 6, 8 and 12 weeks.

RESULTS

In the initial 3 weeks, iopanoic acid induced a significantly greater fall in mean serum total T3 levels (Z = 2.298, p < 0.02) and a slower fall in mean serum total T4 (Z = 2.396, p < 0.05) in group A patients compared to those in group B. This was accompanied by earlier clinical improvement in group A patients. The mean serum total T3 and T4 values rose to higher levels in group A at 4 weeks, one week after discontinuation of iopanoic acid. At the end of 12 weeks, however, there was no significant difference in the mean serum total T3 and T4 levels between the two groups (p > 0.05). Biochemical euthyroidism (i.e. total T3 < 3 nmol/L and total T4 < 170 nmol/L) was achieved later in group A patients than in group B (10.4 +/- 5.0 weeks v. 3.6 +/- 1.2 weeks, p < 0.0001).

CONCLUSIONS

Iopanoic acid given together with carbimazole induces rapid clinical improvement in hyperthyroid patients than carbimazole alone. However, the delayed achievement of euthyroidism may preclude its routine use in the management of patients with hyperthyroidism except in those with thyrotoxic emergencies.

Experience with carbimazole in the drug treatment of the hyperthyroidism of Graves' diseases in Nigerians

To estimate the rate of remission of relapse in patients with thyrotoxic Graves' disease following therapy with thionamides, the course of 49 patients who were treated with carbimazole and followed personally for a mean (+/- SD) of 22.0 +/- 17.8 months, was analysed. A remission rate of 61% was obtained. Remissions were more common in patients with small goitres and those with a short duration of illness. Relapse, which was infrequent, occurred mostly within a few months following the discontinuation of the drug. 32% of the patients left the clinic either before or soon after achieving euthyroidism. It is concluded that carbimazole is quite efficacious in the induction or remission in newly diagnosed Nigerian patients with toxic Graves' disease and, at the present time, should probably be the principal treatment modality for these patients rather than subtotal thyroidectomy. Efforts should be made to reduce the frequent drop-out of our patients from the clinic during follow-up.

[The effect of 1-p-bromphenyl-5-mercapto-1,2,3,4-tetrazole (Br FMT) on thyroid gland function in rats]

The effects of the novel potential thyrostatic agent 1-p-bromphenyl-5- mercapto-1,2,3,4-tetrazole (Br-FMT) on the serum levels of thyroxine, thyrotropic hormone (TSH), the content of cyclic adenosine monophosphate (cAMP) in the thyroid gland, the body weight and the weight of the thyroid gland in liver transaminases and the white blood picture in Wistar strain rats were investigated. The effect of Br-FMT was compared with the effect of the well-known thyrostatic agent and goitrogen ethylester of 3-methyl-2-thio-4-imidazoline-1- carboxylic acid, carbimazole (Spofa) and with the control group, which received placebo only. The drugs tested were administered to animals in the dose do 7.5 mumol/animal via a gastric tube for the period of one month. Br-FMT and carbimazole decreased the level of serum thyroxine in a statistically significant manner. The serum level of TSH was evidently decreased after Br-FMT; it was not changed after administration of carbimazole in the given dose. The content of cAMP in the thyroid gland was significantly increased only after carbimazole. The weight of the thyroid gland was not significantly changed in any group under study, though after carbimazole the mean value was higher by a quarter as compared with the control group. The body weight and white blood picture were not significantly changed in all groups under study. ALT and AST values were evidently lower after carbimazole and Br-FMT, most probably due to the hypothyroid state of the animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Mitosis in the oesophageal epithelium of rats during chronic antithyroid treatment with carbimazole

The mitotic activity of the oesophageal epithelium of male rats maintained under carefully controlled conditions was studied, using the metaphase-arrest agent, vincristine sulphate. The accumulation of metaphases was linear (r = 0.97). In untreated rats there was a clear mitotic rhythm with a peak metaphase index (expressed as a percentage) of 12.4 +/- 0.86 (S.E.M.) at 12.00-15.00 h and a trough of 1.3 +/- 0.35 at 24.00 h. The overall mean metaphase index was 5.4 +/- 0.76. The effect of treatment with the antithyroid agent, carbimazole (0.1 g/100 ml in the drinking water), for 3 weeks was to depress the higher values at 12.00-18.00 h (P less than 0.01), while leaving the overall index unchanged. Carbimazole caused a significant (P less than 0.01), transient 40% increase in the metaphase index after 2 days; thereafter the metaphase index remained at control levels until 12 weeks of treatment when a steady decline occurred until 24 weeks. The results are in contrast to those in previously described experiments on thyroid follicular cells which show a large increase in the first few days of treatment, followed by a steady decline towards control levels at 12 weeks. The metabolic activity of the animals is about 50% of normal at 12 weeks when both the oesophageal epithelium and the thyroid follicular cells begin to show a reduction in proliferative activity.

Plasma neuropeptides in hyperthyroidism

Plasma levels of the neuropeptides, vasoactive intestinal polypeptide (VIP, neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), substance P, and galanin were determined in 15 hyperthyroid patients before and at 3 occassions during 38 weeks of treatment. Treatment was performed with either 131I alone or with carbimazole, with combination of carbimazole and thyroxine, or with subtotal thyroidectomy. Before and after 11 (+/- 4), 24 (+/- 6) and 38 (+/- 5) weeks of treatment, plasma neuropeptide levels were analysed. A group of 9 premenopausal women served as controls. During hyperthyroidism, mean plasma level of CGRP was higher than in controls (P less than 0.001). In contrast, the mean plasma levels of the other measured neuropeptides did not differ from those in the controls. Mean serum level of tree T4 was lowered from 81.9 +/- 30.1 to 23.9 +/- 8.6 pmol/l and mean serum level of free T3 was lowered from 27.3 +/- 7.9 to 6.7 +/- 2.3 pmol/l during the course of the treatment. After 11 weeks of treatment, mean plasma NPY level was significantly increased (P = 0.004) compared to pretreatment levels. However, after 38 weeks of treatment, mean plasma NPY level had returned to control values. The mean plasma CGRP level was significantly reduced at 11 and 38 weeks of treatment compared to pre-treatment value (P = 0.002 and P = 0.004, respectively). Mean plasma level of neurotensin slowly declined during the treatment (P = 0.003). In contrast, mean plasma level of VIP, of substance P, and of galanin did not differ from control value before or after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

[An attempt to substitute carbimazole for Alkiron in an atherogenic diet]

Due to present unavailability of Alkiron the authors tried to substitute it by Carbimazole in atherogenic diet aimed at inducing advanced atherosclerosis in rats. Carbimazole proved to be entirely ineffective in this respect and thus the thiouracil derivatives cannot be substituted by it.

Humoral and cellular immunological factors as possible markers of clinical relapse in HLA-typed Graves' patients followed with time

Humoral and cellular immune factors were studied in 33 newly diagnosed Graves' patients at diagnosis and in 12 of these patients at regular intervals thereafter. All the patients were treated with carbimazole for 15 months (initially 60 mg and then 20 mg supplemented with L-Thyroxine). The incidence of relapse after treatment was 42%. Thyrotropin receptor antibodies (TRAb), T-cell subsets, K and NK cells and mononuclear cells expressing surface antigen markers of different activation were evaluated respectively by the use of a radioimmunoassay and a panel of monoclonal antibodies. Patients in the follow-up study were HLA-A, B, C and D typed. TRAb levels (91%) and levels of 4F2-positive cells (73%) and class II-positive lymphocytes (69.6%) were significantly increased in newly diagnosed Graves' patients in comparison with normal controls, whereas CD8 cells were significantly decreased. There was a significant inverse correlation between the increase in 4F2-positive cells and TRAb values. In the follow-up study both humoral and cellular immunological parameters showed a wide variation in levels, but TRAb, 4F2 and L243 values declined on average with respect to diagnosis. After 15 months some patients still showed abnormal values of activated T cells and TRAb values. All patients who relapsed (42%) after medical treatment showed a significant increase of 4F2-positive cells, and some of TRAb, some time before the appearance of clinical symptoms. Finally, no correlation was found between HLA type and relapse of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of HLA-DR expression on cultured human thyrocytes: effect of antithyroid drugs and other agents on interferon-gamma-induced HLA-DR expression

There have been conflicting reports on whether antithyroid drugs (ATD) act as immunosuppressive agents in patients with autoimmune thyroid disease. While some have claimed that methimazole (MMI) affects the immune system directly, we and others have suggested that its apparent immunosuppressive activity is due to its ability to inhibit thyrocyte, rather than immunocyte, activity. To further address the question, we studied the action of ATD on interferon-gamma (IFN gamma)-induced HLA-DR expression on thyrocytes in tissue culture. We used a cytotoxicity assay, using chromium-51-labeled Graves' disease (GD) thyrocytes and normal thyrocytes incubated sequentially with a monoclonal antibody against HLA-DR and complement, with a cytotoxicity index as the measure of thyrocyte HLA-DR expression. MMI and propylthiouracil (PTU) were added along with 200 U/mL IFN gamma to thyrocytes cultured for 10-14 days. IFN gamma or supernatants from leukoagglutinin-stimulated peripheral blood mononuclear cells (PBMC) stimulated thyrocyte HLA-DR expression; however, the addition of MMI or PTU to either the PBMC or thyrocytes caused no inhibition of the IFN gamma or PBMC IFN gamma stimulation of thyrocyte HLA-DR expression, using either normal or GD thyrocytes. Potassium perchlorate and sodium iodide also had no effect on IFN gamma-induced thyrocyte HLA-DR expression. TSH (either bovine or human) did not induce HLA-DR expression on thyrocytes by itself, but did enhance IFN gamma-induced HLA-DR expression in normal, but not GD, thyrocytes; once again, the further addition of MMI or PTU did not inhibit the enhancing effect of TSH on thyrocyte HLA-DR expression. Low concentrations of TSH binding inhibitory immunoglobulin (TBII; 100 micrograms/mL) did not alter the cytotoxicity index, but at 400 micrograms/mL or more it enhanced HLA-DR expression on normal, but not GD, thyrocytes in a manner similar to TSH; like TSH, it did not induce thyrocyte HLA-DR expression by itself. Moreover, addition of MMI to the combination of IFN gamma and TBII did not inhibit the response of thyrocytes in terms of HLA-DR expression. We conclude that ATD do not alter thyrocyte HLA-DR expression in vitro; however, the ATD may still cause immune effects in vivo secondary to their influence on thyroid hormone formation or synthesis or by inhibition of thyroid antigen presentation which indirectly may result in an immunomodulatory effect. While TSH and TBII similarly enhanced the IFN gamma-induced expression of HLA-DR on normal thyrocytes, they did not do so in GD thyrocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Normal suppressive T cell function of Epstein-Barr virus-induced B cell activation in Graves' disease

Several studies have demonstrated abnormalities of T cell regulation of Epstein-Barr virus (EBV)-induced B cell activation in systemic autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis. To investigate whether this abnormality is a common feature of other autoimmune diseases, we studied 10 EBV-immune normal subjects and 22 EBV-immune patients with Graves' disease (GD); 11 had newly diagnosed hyperthyroidism, and 11 had received carbimazole treatment for hyperthyroidism for at least 6 months. Peripheral B lymphocytes infected with EBV were cultured for 20 days in the presence or absence of autologous T cells at different ratios. Immunoglobulins M and G secretion into the supernatants was determined using an enzyme-linked immunosorbent assay. The extent of suppression when T cells were added, as measured by a suppression ratio, was not significantly different in normal subjects and newly diagnosed GD patients (0.65 vs. 0.63 on the 16th day and 0.77 vs. 0.72 on the 20th day of culture, respectively). In carbimazole-treated patients, the appearance of functional suppressor T cells was delayed slightly, but the overall suppression ratios on the 16th and 20th days were normal. Thus, a T cell regulation abnormality of EBV-induced B cell activation could not be demonstrated in patients with untreated hyperthyroid GD, suggesting that the autoimmune reactivity in such patients is probably dependent upon a specific thyroid suppression defect rather than a generalized suppression defect.

The effect of carbimazole on growth and sexual maturity in the pullet

Carbimazole (100 mg/kg diet) was fed to pullets from 8 to 12 or from 12 to 16 weeks of age. Pullets fed carbimazole from 8 to 12 weeks of age matured about 12 d earlier and produced more eggs between 17 and 22 weeks of age. Their body weights and feed intake were significantly lower than those of normal birds. Feeding carbimazole from 12 to 16 weeks of age had no significant effect on the birds except during the course of treatment where their feed consumption was less than that of the controls.

Thyroid stimulating immunoglobulin (TSI) synthesis by pokeweed mitogen (PWM) stimulated peripheral blood lymphocytes (PBL) from Graves' disease (GD) patients

Lymphocytes from freshly diagnosed untreated GD patients can be induced to produce in-vitro IgG, and more precisely TSI in the presence of PWM, a T cell dependent polyclonal activator of B cells. TSI were measured from days 8 to 41 of culture, using a functional cAMP production assay, after the deposition of culture supernatants on HTEC. Spontaneous or PWM induced IgG synthesis was optimal on day 28 of culture for GD MNC, with amounts of IgG in PWM stimulated GD culture supernatants twice those found in unstimulated GD MNC. Moreover only PWM stimulated GD MNC produce IgG which induce cAMP production by cultured HTEC, with a significant correlation between in-vitro IgG and cAMP levels.

Kinetics of [123I]iodide uptake and discharge by perchlorate in studies of inhibition of iodide binding by antithyroid drugs

Thyroidal binding of iodide was studied by kinetic analysis of [123I]iodide uptake and its discharge by perchlorate in 80 hyperthyroid subjects receiving antithyroid drug therapy. Five dosage regimens ranging from 5 mg carbimazole twice daily to 15 mg methimazole twice daily were studied. Binding inhibition was estimated at 5-7 h after drug as an index of the mean effect of the 12 hourly regimen. In all cases, except one in the lowest dose group, binding was found to be markedly reduced with mean binding rates ranging from 0.002 to 0.020 min-1 (normal greater than 0.15 min-1). The net clearance of iodide in the lowest dose group was reduced to a mean value near the upper limit of the euthyroid range, whereas in the highest dose group it lay at the lower limit of the euthyroid range. These results were reflected in the serum thyroid hormone response. There was a reducing incidence of inadequate control of hyperthyroidism and an increasing incidence of hypothyroidism with increasing thiourylene dose. The exit rate constant of free iodide for the various doses showed values from 0.048 to 0.055 min-1. Corresponding mean values for the discharge rate constant after perchlorate were 0.087 to 0.105 min-1. This suggests that perchlorate increases the rate of iodide release from the thyroid gland. Studies at a later interval after drug (12-14 h) showed no change in discharge rate constant. This leads to the conclusion that perchlorate may further inhibit iodide binding in subjects receiving antithyroid drug therapy.

Interactions of beta-adrenoceptor antagonists and thyroid hormones in the control of heart rate in the dog

Propranolol, sotalol and nadolol have been infused into conscious dogs, and doses at which the three drugs are equipotent as beta-adrenoceptor antagonists determined. In euthyroid dogs, sotalol was more effective at lowering heart-rate than an equivalent dose of propranolol, while an equivalent dose of nadolol was without effect. Hyperthyroidism potentiated the lowering of heart-rate by sotalol, but inhibited that by propranolol. The effect of sotalol on heart-rate was correlated with its prolongation of the Q-T interval of the ECG. That of propranolol was correlated with its prolongation of the P-R interval. Nadolol did not affect P-R interval or Q-T interval except at relatively high dosage. We conclude that the tachycardia of hyperthyroidism is not affected by blockade of beta-adrenoceptors and therefore that it is not mediated by adrenergic mechanisms. The effectiveness of propranolol and sotalol in lowering heart-rate must be due to actions peculiar to those drugs, and not to beta-adrenoceptor antagonism.

The effect of carbimazole on thyroid autoantibody synthesis by thyroid lymphocytes

Thyroid autoantibody synthesis was investigated in cultures of lymphocytes isolated from several sources, including thyroid and lymph nodes from patients with hyperthyroid Graves' disease treated preoperatively with carbimazole or propranolol. The ability of thyroid lymphocytes to secrete immunoglobulins, including thyroid microsomal or thyroglobulin autoantibodies, was markedly reduced in lymphocyte suspensions obtained from patients treated with carbimazole compared with suspensions from patients treated with propranolol. This effect (which was greater in individuals treated with carbimazole for longer periods) was attributable to a significant reduction in the number of viable lymphocytes present after the 14-day culture interval. In contrast, the type of preoperative therapy had little effect on cultures of lymphocytes obtained from lymph nodes draining the thyroid. Although it is not yet clear whether carbimazole exerts its effects in vivo by direct immunosuppression or indirectly by altering the thyroid microenvironment, our observations indicate that the fall in serum levels of thyroid autoantibodies that occurs during carbimazole therapy is related to an effect of the drug on lymphocytes within the thyroid.

Inhibition of the receptor for interleukin-2 induced by carbimazole: relevance for the therapy of autoimmune thyroid disease

Evidence has been accumulated that the anti-thyroid drugs used in the treatment of Graves' disease may have immunosuppressive properties but the exact mechanism of action is still unclear. In the present study, we have investigated the in vitro effect of carbimazole (CBZ) on the expression of lymphocyte differentiation antigens and on suppressor cell activity. The incorporation of radiolabelled methimazole (35S-MMI, the active metabolite of CBZ) by resting and mitogen stimulated lymphocytes was also investigated. CBZ at concentrations of 60 microM significantly inhibited the expression of the receptor for interleukin-2 (as defined by the anti-TAC monoclonal antibody [MoAb]) by lymphocytes stimulated with phytohaemagglutinin. The expression of an early activation antigen (as characterized by the 4F2 MoAb) was not affected. Twenty-four hour pre-incubation of cells with different concentrations of CBZ or medium alone did not change the lymphocyte response to mitogenic stimulation, thus suggesting no effect of the compound on suppressor cell function. Finally, there were no significant differences in the uptake of 35S-MMI between resting and stimulated lymphocytes. These data suggest that the immunosuppressive effect of CBZ may be due to its effect of reducing the expression of the receptor for interleukin-2 on lymphocytes undergoing full activation. This property of CBZ could be of relevance in the therapy of autoimmune thyroid diseases (not only Graves' disease) which are characterised by the presence of activated T cells in the thyroid and in circulation.

Analysis of T cell subsets in Graves' disease: alterations associated with carbimazole

Conflicting data on subpopulations of peripheral blood lymphocytes in patients with autoimmune disease largely reflect variations in methods of study. An investigation was therefore conducted aimed at avoiding this difficulty. Serial samples of peripheral blood mononuclear cells from 42 patients with hyperthyroid Graves' disease were collected at monthly intervals before, during, and for 12 months after a six month course of carbimazole. Samples were stored in liquid nitrogen until completion of the study, when they were thawed and all samples from each patient analysed within the same assay using mouse monoclonal antibodies to human cell subsets and a fluorescence activated cell sorter. Proportions of cytotoxic/suppressor (OKT8) positive cells before treatment (mean 17.4 (SEM 0.8)%) were significantly lower (p less than 0.001) than those in normal controls (29.8 (1.9)%; n = 10) and returned to normal by the end of treatment. In contrast, the proportions of activated T cells (OKIa-OKM1) were significantly raised before treatment as compared with normal (14.4 (0.6)% versus 4.6 (0.8)%; p less than 0.001) and fell to normal by the end of treatment. Proportions of OKT3 and OKT4 positive T cells remained unchanged throughout treatment and in the succeeding 12 months. In patients who relapsed after treatment there was a rise in the proportion of activated T cells and a fall in OKT8 positive T cells, which returned towards normal with retreatment. The explanation for the alterations in numbers of circulating T cells remains to be determined but they may provide a means for predicting more accurately the outcome of Graves' disease after treatment with carbimazole.

The effect of altered thyroid status on lipid metabolism in Nubian goats

The effects of triiodothyronine (T3)-induced hyperthyroidism and of carbimazole (CZ)-produced hypothyroidism on lipid metabolism were studied in Nubian goats (Capra hircus). T3 treatment decreased the serum, liver and heart triglyceride, cholesterol and phospholipid concentrations. These changes were accompanied by an increase in the activity of lipoprotein lipase (LPL) in the heart and skeletal muscles. CZ treatment at a dose of 90 mg/goat significantly increased the serum triglyceride, liver cholesterol and heart phospholipid. CZ treatment significantly increased the liver and heart triglyceride concentration but the activity of LPL was not affected.

Reversible and irreversible inhibition of thyroid peroxidase-catalyzed iodination by thioureylene drugs

The mechanism of reversible and irreversible inhibition of thyroid peroxidase (TPO)-catalyzed iodination by thioureylene drugs was investigated using a model incubation system. The major observations may be summarized as follows. 1) TPO is inactivated by 1-methyl-2-mercaptoimidazole and propylthiouracil even in the presence of a relatively high concentration of iodide. The extent of this inactivation depends on the ratio of iodide to drug. 2) Spectral changes observed on oxidation of the drugs with the peroxidase-iodide system were very similar to those observed when the drugs were oxidized nonenzymatically with I3-. These findings support the view that oxidized iodine is an intermediate in TPO-catalyzed oxidation of the drugs. 3) Under conditions where TPO is largely inactivated, inhibition of iodination is complete and irreversible. Drug metabolism, on the other hand, occurs to a limited extent. 4) Under conditions where TPO is only partially inactivated, inhibition of iodination is transient (reversible). In this case, drug metabolism is extensive, and higher oxidation products (sulfate and sulfinic acid) are observed. Inhibition of iodination occurs only during the interval required to reduce the drug concentration to a low level. Thereafter, iodination may occur at a rate close to that observed in the absence of drug. Based on these and other observations, a scheme is presented to explain the mechanism of reversible and irreversible inhibition of iodination. In essence, the type of inhibition depends on the relative rates and extent of TPO inactivation and drug oxidation. These rates, in turn, depend primarily on the iodide to drug concentration ratio. A high ratio favors extensive drug oxidation and reversible inhibition. A low ratio favors TPO inactivation and irreversible inhibition.

[Reaction of autonomous and non-autonomous thyroid tissue to iodination blockers]

In the case of thyrostatic therapy of autonomous adenoma with iodinization blocker type drugs (here carbimazol), there is a relative increase of uptake of 99mTc-pertechnetate by the suppressed thyroid tissue before TSH becomes detectable by TRH testing (400 micrograms). As soon as endogenous TSH stimulation occurs (due to the decrease of thyroid hormone induced by the thyrostatic therapy), relatively more uptake of 99mTc-pertechnetate by the non-autonomous tissue is observed. 56 patients suspected of having autonomous thyroid adenoma were investigated. The activities in the regions of interest measured over autonomous and non-autonomous thyroid tissue before and after thyrostatic therapy were expressed in form of a double-ratio. 22 of the 56 patients were found to have an autonomous adenoma (double-ratio greater than or equal to 1.74). In 19 patients an adenoma was excluded with certainty (double-ratio less than or equal to 1.22). The remaining cases fell in-between and were difficult to classify. However, the gradual transition between the two groups so classified was harmonious. The different reactions of autonomous and non-autonomous thyroid tissue to thyrostatic therapy appear to be helpful in the differentiation between the two types of tissue.

Defects in intrathyroid binding of iodine and the perchlorate discharge test

The kinetics of [123I]iodide uptake were studied when organification of iodine by the thyroid gland was normal and when this binding function was diminished by drugs or disease. Each study was terminated by a sodium perchlorate discharge test (300--600 mg iv) at 60 min or, in some cases, 10--30 min. The results confirmed that binding takes place rapidly in the uninhibited gland with the binding rate constant being at least 0.150 min-1. Discharge from the uninhibited gland is less than 3.5% of the gland uptake when perchlorate is given 60 min after the radioiodide. Subjects with an intrinsic binding defect manifested discharges of 11% of greater of the 60 min uptake and the estimated binding rate constants ranged from 0.003--0.057 min-1. Thyrotoxic subjects receiving 5 mg carbimazole twice daily manifested discharges ranging from 5.4--64.2%, and in those receiving 20 mg twice daily the observed discharges were 67.6--94.6% of the 60 min uptake. The study shows that a correctly performed perchlorate discharge test will detect minimal inhibition of iodine binding. An important factor is the duration of the follow-up period after perchlorate is given. In some of the cases studied discharge was not complete until 60 min after the perchlorate.

Inhibition of killer cell cytotoxicity induced by carbimazole in vitro

The in vitro effect mediated by carbimazole (CBZ), a classical anti-thyroid agent on the antibody dependent cellular cytotoxicity (ADCC), low affinity E-rosetting cells (E-RFC) and high affinity E-RFC was investigated using lymphocytes from 11 normal subjects. CBZ at the doses of 250 and 500 mumol/l significantly reduced ADCC in all subjects studied. Low affinity E-RFC--mainly cells possessing receptors for the Fc portion of IgG and expressing cytotoxic properties in the ADCC system--were also significantly reduced following incubation with the same CBZ doses. These results suggest that CBZ, in addition to the known inhibitory effect on thyroid hormone synthesis, may be useful by depressing lymphocyte cytotoxicity in the treatment of autoimmune thyroid disease.

Intrathyroidal iodide binding rates and plasma methimazole concentrations in hyperthyroid patients on small doses of carbimazole

1 The effect of small doses of carbimazole on the binding rate constant of intrathyroidal iodide, plasma methimazole concentrations and circulating thyroid hormone concentrations in five hyperthyroid patients is presented. 2 In all patients there was a marked reduction in iodide binding with carbimazole doses as low as 5 to 10 mg daily. 3 In three patients little further reduction in the observed binding rate occurred with daily doses in excess of 10 mg despite progressive increases in plasma methimazole concentrations. 4 At the end of 4 weeks' treatment with 10 mg carbimazole daily, the reduction in thyroid hormone concentrations and clinical improvement were such as to suggest that this dose may be an effective starting dose in many patients.

Thyroid proliferation, body weight, thyrotropin and thyroid hormones in chronic antithyroid (carbimazole) treatment in rats

Male rats (200 g body weight) were either untreated or given carbimazole (0.1 g/100 mg) in their drinking water for up to 24 weeks. Vincristine sulphate - a metaphase arrest agent - was used to estimate the mitotic activity of thyroid follicular cells. Measurements of body growth rate and oxygen consumption showed that the animals were hypothyroid after one week of treatment. The relationship between body growth and mitotic rate supports the concept of the thyroid follicular cells as an 'expanding' cell population. The mitotic rate (metaphases/10(4) cells . hour +/- S.E.) rose from the control level of 3.9 +/- 1.28 to 33.3 +/- 7.59 after 2 days of treatment and reached a peak of 79.9 +/- 8.56 on day 5. Thereafter, it declined slowly, but remained significantly greater than control levels until the 16th week of treatment. Changes in mitotic activity were accompanied by characteristic histological changes in the gland. After two days' treatment with carbimazole, the serum concentration of thyrotropin (TSH) was significantly increased and the serum levels of tri- and tetra-iodothyronine were decreased. These results area compared with those of earlier studies and discussed in relation to changes in hormone levels and strongly suggest that TSH is responsible for the hyperplasia of thyroid follicular cells to respond to continued stimulation.