Accumulation Of Thyroxine Research Articles

Role of thyroid dysimmunity and thyroid hormones in endometriosis

Endometriosis is characterized by the presence of ectopic endometrial cells outside the uterine cavity. Thyroid autoimmunity has been associated with endometriosis. This work investigated the potential pathophysiological link between endometriosis and thyroid disorders. Transcripts and proteins involved in thyroid metabolism are dysregulated in eutopic and ectopic endometrium of endometriotic patients, leading to resistance of ectopic endometrium to triiodothyronine (T3) action and local accumulation of thyroxine (T4). Thyroid-stimulating hormone (TSH) acts as a proliferative and prooxidative hormone on all endometria of endometriosis patients and controls, whereas T3 and T4 act to specifically increase ectopic endometrial cell proliferation and reactive oxygen species (ROS) production. Mouse studies confirmed the data gained in vitro since endometriotic implants were found to be bigger when thyroid hormones increased. A retrospective analysis of endometriosis patients with or without a thyroid disorder revealed an increased chronic pelvic pain and disease score in endometriotic patients with a thyroid disorder.

Possible mechanism for the polychlorinated bipheny-linduced liver-selective accumulation of thyroxine in rats.

We have previously reported that decrease in level of serum thyroxine T4 by Kanechor 500 (KC500) in rats would occur through the increase in hepatic T4 accumulation rather than the increase in hepatic T4-glucuronyl transferase activity. In the present study, to understand the mechanism underlying the KC500-mediated increase in hepatic T4 accumulation, we examined the relationship between the KC500-mediated changes in hepatic T4 accumulation and the expression levels of mRNAs of hepatic transporters including T4 transporters. [125I]T4 was intravenously injected into KC500-pretreated and control (KC500-untreated) Wistar rats, and [125I]T4 uptake levels of liver parenchymal cells were comparatively examined. The amount of [125I]T4 uptake by hepatic cells increased in a time-dependent manner up to 96 hr after KC500 treatment. Following KC500 treatment, a time-dependent increase in the mRNA level of hepatic T4 influx transporter LAT1 was observed up to 96 hr later, while a significant increase in hepatic T4 influx transporter Oatp2 mRNA occurred only at 96 hr later. No KC500-mediated increases in the mRNAs of other hepatic transporters (Oatp1, Oatp3, Oatp4, Ntcp, LAT2, and Mrp2) were observed at any timepoints, although the mRNA expression of the T4 conjugate(s) efflux transporter Mrp3 significantly increased in a time-dependent manner 24-96 hr following KC500 treatment. The present findings suggest that KC500-mediated increase in hepatic T4 accumulation occurs, at least in part, through the increase in the expression of hepatic T4-transporters, such as LAT1 and Oatp2.

3,3′,4,4′-Tetrachlorobiphenyl-Mediated Decrease of Serum Thyroxine Level in C57BL/6 and DBA/2 Mice Occurs Mainly through Enhanced Accumulation of Thyroxine in the Liver

A single intraperitoneal injection (50 mg/kg) of 3,3',4,4'-tetrachlorobiphenyl (CB77), a 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-type polychlorinated biphenyl, led to significant decreases in the levels of serum total thyroxine (T4) and free T4 without increase in the level of serum thyroid-stimulating hormone at 7 d later in both TCDD-sensitive C57BL/6 and TCDD-resistant DBA/2 mice. When [(125)I]T4 was injected into the mice 7 d after treatment with CB77, the levels of biliary [(125)I]T4 and [(125)I]T4-glucuronide increased 90 to 120 min post injection in C57BL/6 mice, but not in DBA/2 mice, compared with levels in the corresponding control mice. In contrast, in both strains of mice, the CB77-pretreatment led to similar changes in the levels of the [(125)I]T4 bound to the serum transthyretin, albumin, and thyroxine-binding globulin. Consequently, treatment with CB77 promoted the clearance of [(125)I]T4 from the serum and further raised the steady-state volumes of distribution of [(125)I]T4, the concentration ratio (Kp value) of the liver to the serum, and the distribution of [(125)I]T4 in the liver in both strains of mice. The present findings indicate that in mice, the CB77-mediated decrease in the serum T4 level occurs through enhanced accumulation of hepatic T4 rather than through increased activity of hepatic thyroxine-uridine 5'-diphosphate-glucuronosyltransferase(s).

4-Hydroxy-2,2′,3,4′,5,5′,6-heptachlorobiphenyl-Mediated Decrease in Serum Thyroxine Level in Mice Occurs through Increase in Accumulation of Thyroxine in the Liver

4-Hydroxy-2,2',3,4',5,5',6-heptachlorobiphenyl (4-OH-CB187) was selected as a major hydroxylated polychlorinated biphenyl metabolite detected from serum of wildlife and humans and was examined for its effect on level of serum thyroid hormone in mice. Four days after treatment of C57BL/6 and DBA/2 mice with 4-OH-CB187 (1.0 mg/kg), the serum total thyroxine (T(4)) and free T(4) levels were decreased in both strains of mice. On the other hand, no significant changes in the level and activity of the T(4)-UDP-glucuronosyltransferases, including UGT1a and UGT1a1, by the 4-OH-CB187 treatment were observed in either strain of mice. No 4-OH-CB187-mediated change in level of serum thyroid-stimulating hormone was observed in either strain of mice. Binding levels of [(125)I]T(4) to serum proteins after administration of [(125)I]T(4) were significantly changed in 4-OH-CB187-pretreated mice: a decrease in the level of serum [(125)I]T(4)-transthyretin (TTR) complex and an increase in the binding level of [(125)I]T(4) to serum albumin and thyroxine binding protein in both strains of mice. Clearance from serum of T(4) was promoted by 4-OH-CB187 pretreatment in both C57BL/6 and DBA/2 mice, and the levels of T(4) in several tissues, especially the liver, were increased. In addition, 4-OH-CB187-mediated decreases in serum total T(4) and free T(4) levels were observed in wild-type and TTR-heterozygous mice but not in TTR-deficient mice. The present findings show that 4-OH-CB187 shows a definite ability to decrease serum T(4) level and further indicate that the 4-OH-CB187-induced decrease would occur through increase in accumulation of T(4) in the liver.

Evaluation of mechanisms inducing thyroid toxicity and the ability of the enhanced OECD Test Guideline 407 to detect these changes

The OECD has developed an "enhanced Test Guideline 407" (TG 407) protocol for detecting endocrine effects during the course of a 28-day testing scheme. This protocol has gone through a validation process with (anti)estrogenic and (anti)androgenic compounds and substances that affect the thyroid (thyroxine and propylthiouracil). This review investigates whether a 28-day testing scheme would show up alterations in the thyroid-related parameters of the "enhanced TG 407" (T3, T4, TSH, thyroid weight and histopathology), irrespective of the mode of action. For each mode of action, a generally accepted reference chemical was selected and an in-depth literature survey was carried out, and the chemical was evaluated for treatment-related changes of thyroid-dependent parameters. The following model chemicals were selected: ion perchlorate, blockage of iodine uptake; propylthiouracil, inhibition of thyroid hormone synthesis; excess of iodine, blockage of thyroid hormone release; pyrazole, thyroid cytotoxicity; minocycline, thyroid pigmentation; amiodarone, inhibition of TSH synthesis; diethylstilbestrol, competition for thyroid hormone binding globulin; selenium-deficient diet, inhibition of thyroxine deiodination; FD&C Red No. 3, inhibition of peripheral 5'-deiodinase; cadmium, lipid peroxidation; phenobarbital, increase in thyroxine conjugation and biliary excretion; temelastine, thyroxine accumulation. Test data for treatments lasting approximately one month were available for most of these model chemicals, and these demonstrated the expected thyroid-related changes. Thus, it can be concluded that a 28-day testing scheme allows for the detection of thyroid-disrupting chemicals. The literature data also were evaluated according to whether preference can be given to any of the thyroid-related parameters (thyroid/pituitary hormones, thyroid weight and histopathology) with regard to dose-related sensitivities. Due to different study designs (such as treatment duration, application mode, dose selection and parameters used), no clear picture emerged. Therefore, consideration should be given to all of these parameters, which should also help to define the mode of action. Overall, this literature review provides support for the contention that the newly developed "enhanced TG 407" test protocol is well suited to the detection of chemicals that affect the thyroid gland.

Modulation of thyroxine uptake and efflux in vitro by temelastine and phenobarbital in cultured hepatocytes from different species, in relation to toxicological effects on the thyroid gland

Toxicological studies in the rat with phenobarbital and temelastine (SK&F 93944) are associated with thyroid lesions, characterized by thyroid stimulated hormone-mediated thyroid follicular cell hypertrophy and hyperplasia. It has previously been demonstrated that these compounds enhance the hepatocellular accumulation and clearance of thyroxine (T 4), in rat but not dog or mouse. In this study these events were further characterized in vitro using cultured hepatocytes from different species. Exposure of rat hepatocytes in vitro to phenobarbital and temelastine produced significant increases ( P < 0.05) in hepatocellular [ 125I] l-thyroxine accumulation, following 3 hr of exposure to either drug (at a concentration of 10 μ m), in the presence of [ 125I]T 4 (0.107 n m final concentration). At this concentration the accumulation of [ 125I]T 4 after xenobiotic exposure was 132.6 ± 1.5% (phenobarbital) and 135 ± 2.0% (temelastine) of control values. There was no apparent xenobiotic-induced cytotoxicity (as determined by the mitochondrial MTT index) up to 20 μ m temelastine and 50 μ m phenobarbital in rat hepatocytes. Experiments performed at 4°C [or under conditions of cellular ATP depletion, induced by 1 μ m carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP) treatment] failed to show any such increase in hepatocellular thyroxine accumulation. Pretreatment of hepatocytes with either phenobarbital or temelastine for 3 hr before the addition of radiolabelled thyroxine produced increases in hepatocellular hormone accumulation similar to those observed when [ 125I]T 4 and drug were added to the cultures simultaneously. The earliest time at which any increase in [ 125I]T 4 accumulation was observed after drug exposure was approximately 90 min. Exposure of hepatocytes from guinea pig or beagle dog to phenobarbital or temelastine in vitro failed to produce similar increases in hepatocellular [ 125I]T 4 accumulation, demonstrating species specificity of the xenobiotic effect in vitro.

In vivo biliary excretion and in vitro cellular accumulation of thyroxine by rats or cultured rat hepatocytes treated with a novel histamine H1-receptor antagonist

Rats treated with temelastine (SK&F 93,944), a novel histamine H1-receptor antagonist, develop thyroid lesions characterized by hypertrophy and colloid depletion. To investigate the mechanism underlying the lesion the biliary clearance and hepatocellular accumulation of radio-labelled iodothyronines was measured in rats or cultured rat hepatocytes. Treatment with temelastine increased both the biliary clearance (approximately 300% of control) and hepatocellular accumulation (approximately 200%) of thyroxine (T4) but had little or no effect on tri-iodothyronine (T3). Chromatographic analysis of bile samples from temelastine-treated rats showed that the majority (approximately 78%) of T4 was present in the unconjugated form. This contrasted with data from phenobarbitone-treated rats which showed that approximately 80% of T4 in the bile was present as the glucuronide conjugate. Studies with cultured hepatocytes showed that the hepatocellular accumulation of T4 was energy dependent. At 4 degrees C the treatment-related increases in accumulation of T4 were abolished, suggesting that temelastine is specifically affecting the high affinity, energy dependent system which preferentially transports thyroxine into hepatocytes. Because temelastine is metabolized extensively, investigations were undertaken to discover if the hepatic effects were caused by the parent compound or an oxidative metabolite. The results showed that the hepatocellular accumulation of T4 remained increased in hepatocytes co-incubated with temelastine and 1-aminobenzotriazole (a suicide inhibitor of cytochrome P450), even though no measurable P450 could be found in the cells. Also, in studies with two major "rat" metabolites of temelastine, i.e. 93,944-Met I or 93,944-Met VIII, treatments failed to reproduce the responses seen with the parent compound.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro accumulation of thyroid hormones by cultured rat hepatocytes and the biliary excretion of iodothyronines in rats treated with a novel histamine H 2-receptor antagonist

The administration of SK&F 93479, a novel histamine H 2 antagonist, to Wistar rats has been shown to produce thyroid lesions associated with an increased clearance of plasma thyroxine (T 4) and elevated plasma TSH concentrations. To determine if these changes were mediated via an increase in the hepatic clearance of thyroid hormones, the biliary clearance and hepatic accumulation of iodothyronines were measured in rats and cultured hepatocytes treated with SK&F 93479. Both the in vitro and in vivo results showed that treatment with SK&F 93479 caused an increased hepatic accumulation (approx. 200% of control) and biliary excretion (2–3-fold control values) of T 4 but had little or no effect on T 3 uptake. The in vitro studies showed that the treatment related increase in hepatic thyroxine accumulation was temperature and therefore probably energy dependent, while inhibition of cytochrome P-450 dependent enzyme activity did not alter the accumulation of T 4 suggesting that the parent compound and not some oxidative metabolite was responsible for the hepatic effects. Chromatographic analysis of bile from SK&F 93479 and phenobarbitone-treated rats showed that in the latter animals 81% of the T 4 was present as the glucuronide conjugate (consistent with enzyme induction) whereas in the SK&F 93479-treated rats only 25% was present as the conjugate with 75% being in the unconjugated form. These studies show that SK&F 93479 increases the hepatic accumulation and biliary clearance of T 4 by a novel mechanism not associated with liver microsomal enzyme induction.

Influence of ethanol on thyroxine accumulation in the hypothalamus, pituitary gland and cerebrospinal fluid in the newborn rabbit.

The effect of ethanol on thyroxine (T4) accumulation in the hypothalamus (H), pituitary gland (P) and cerebrospinal fluid (CSF) has been investigated in 1-15-day-old rabbits. It has been found that H or CSF serum ratios decreased with age by about 2 in the course of 13 postnatal days. Stable T4 resulted in an increase of 125 I-T4 in H, P and CSF. Ethanol per se caused an increase in transfer and accumulation of radiothyroxine or made the changes after loading animals with carrier T4 more pronounced.

Early organogenesis of the embryonic chick thyroid: I. Morphology and biochemistry

Early organogenesis of the embryonic chick thyroid can be separated into five distinct phases. (1) A placode is first recognized at 48 hr in the midventral pharynx. Its cells are compact, undergo extensive blebbing, and possess apical microfilaments. (2) Vesicle formation coincides with the organization of the microfilaments into pronounced bundles with dense midbodies along their lengths. (3) The vesicle detaches from the pharynx, and as the lumen disappears the band of microfilaments dissipates. The primordium now consists of a loose mass of interior cells with a compact surface cell layer. (4) The primordium elongates laterally and divides to form the bilateral glands. (5) After division, mesenchymal and vascular invasion occur constructing the cords which will give rise to follicles. Thyroxine accumulation is first detected with the recognition of the primordium and increases logarithmically until the vesicle begins to detach from the pharynx. Accumulation of hormone then plateaus until invasion occurs and again increases until after hatching. DNA analyses describe a similar profile for cell numbers with a concomitant plateau. Thus, synthesis of thyroid hormones coincides with the appearance of the primordium, is restricted to the primordium, and describes a concerted profile similar to that found in the pancreas (Rutter et al., 1968).

Studies on the accumulation of thyroxine in isolated bovine thyroid cells.

By the use of isolated bovine thyroid cells (ITC), accumulation of T4 in thyroid tissue has been studied. ITC were chosen to disclose this thyroid cell function per se by eliminating the effect of follicular structure and contaminated serum. Cell/medium ratio (C/M) of 125I-T4, used as an indicator of T4 accumulation, was 17.7 when ITC were incubated in Eagle's solution. On the other hand, the ratio in the thyroid slice and erythrocytes was 1.1 and 3.0 respectively. By equilibration chamber method, T4 accumulated more in ITC than in erythrocytes. The observed accumulation of T4 in ITC was reversible when re-incubated with normal human serum. Displacement of 125I-T4 by non-labelled T4 was not observed at the range of added T4 from 10 to 1000 ital. Essentially the same result were obtained when the liver, thyroid slice or erythrocytes were studied. Therefore, the number of T4-binding sites appears to be very large. Increased deiodination of 125I-T4 was observed when 125I-T4 was incubated with ITC, whereas conversion of 125I-T4 to 125I-T3 was not remarkable. It is concluded that ITC obviously concentrate T4 by an entirely different mechanism from that in serum TBP.

The accumulation of albumin-125-I and thyroxine-131-I in wounds.

AbstractThe distribution of 125I‐labelled guinea‐pig albumin and 131I‐thyroxine in skin and wounds of guinea pigs has been investigated in the period 1–72 hrs after the simultaneous injection of the radioactive compounds. The relative amounts of labelled thyroxine and albumin in normal skin and skin‐wounds, old as well as fresh, indicate that these tissues accumulate thyroxine in excess of that brought there on plasma‐proteins; furthermore that the thyroxine accumulation increases in fresh wounds during the experimental period.

Thyroxine accumulation in thyroids of hypophysectomized rats.

Rats were fed a low iodine (Remington) diet for 8 months, after which radioiodine (125I) was mixed with the diet for 130 days. The metabolism of iodine was studied continuously while isotopic equilibrium was approached for 130 days. The large thyroids of control animals contained few follicles and only 4.4% of their thyroidal iodine was in thyroxine (T4) and 5.9% was triiodothyronine (T3). Hypophysectomy after the 60th day of feeding the labeled diet resulted in a continuous increase of iodine and T4 in the thyroid. Following hypophysectomy, the goiters atrophied and the ng of T4 iodine in the thyroid increased to 7.9 times greater than in intact controls; the concentration of T4 iodine increased 58 times greater than in controls while the concentration of T3 iodine increased to 4.3 times greater than in controls. The results suggest that hypophysectomy inhibited the release of T4 to a greater extent than it inhibited the synthesis of T4 in these goiters; the result was that T4 accumulated during involuti...

Hepatic accumulation of 125I-thyroxine in the rat: augmentation by phenobarbital and chlordane.

Phenobarbital and chlordane, administered in dosage schedules known to induce drug-detoxifying enzymes, increased the concentration ratio of 126I-thyroxine between liver and plasma in rats. Since no effects on plasma binding of thyroxine were observed, it is concluded that these drugs stimulate the hepatocellular factors responsible for the reversible accumulation of thyroxine by liver. (Endocrinology 82: 406, 1968)

SUPPRESSION BY THYROXINE OF THE THYROIDAL RESPONSE TO LOCAL COOLING OF THE "HEAT LOSS CENTER".

AbstractThe intravenous injection of thyroxine (about 15 μg/kg b. wt.) was found to have blocked completely the thyroidal response to local cooling of the“heat loss center” after 2 hours in the goat. However, 15 to 20 min after the administration of thyroxine this blockage was still largely incomplete, suggesting that an accumulation of thyroxine has to occur at some site before a full inhibition of TSH release is obtained. The results are discussed in the light of Brown‐Grant's (1957)“feed‐back” hypothesis of the control of thyroid function.

Uptake and binding of thyroxine and triiodothyronine by rat diaphragm in vitro.

Hemidiaphragms from weanling Sprague-Dawley rats were incubated in Krebs-Ringer buffer containing 1.3 x 10–7 m l-thyroxine or l-triiodothyronine labeled with radioiodine. Triiodothyronine uptake was about twice as rapid as thyroxine uptake. The data were consistent with a kinetic analysis based on a two-step process: 1) simple diffusion into the tissue (rate-limiting step) and 2) binding to cellular proteins (a process that occurs very rapidly compared to diffusion). The diffusion constants were calculated to be kd(T4) = 0.153 cm3/min and kd(T3) = 0.352 cm3/min. The data suggest a single species of tissue-binding site with identical tissue-binding capacity and binding affinity for both triiodothyronine and thyroxine. Maximum binding was found to be 28 x 10–4 µm/g tissue and the affinity constant for binding was 1.4 x 104 g/µm. The difference in the rate of accumulation of thyroxine and triiodothyronine appears to be due only to the difference in the diffusion rate. A direct rate equation for the accumulation of thyroid hormone was derived. Points calculated by means of this equation fit remarkably well with the experimental data.

The influence of extracellular thyroxine-binding protein upon the accumulation of thyroxine by tissue slices.

The influence of extracellular thyroxine-binding protein upon the accumulation of thyroxine by tissue slices.