[Epidemiological characteristics and spatio-temporal distribution of pulmonary tuberculosis cases reported in students from Guizhou Province, 2011-2020]

Objective: To analyze the trend of epidemiological characteristics and spatiotemporal distribution of pulmonary tuberculosis (PTB) among smear-positive or other types of students in Guizhou Province from 2011 to 2020, and to provide a reference for improving prevention and control measures. Methods: Data were collected from the Chinese Information System's Notifiable Disease and Tuberculosis Management Information System for disease control and prevention, the Joinpoint 4.9.1.0 software was used to analyze the trend of registration rate; the ArcGIS 10.6 software was used to construct a ring map and to perform spatial autocorrelation analysis; the SaTScan 9.7 software was used for spatial-temporal scan statistics. Results: A total of 32 682 student PTB cases were reported in Guizhou Province from 2011 to 2020, including 5 949 (18.20%) smear-positive cases. Most cases occurred from high school students of 16 to 18 years old (43.99%, 14 376/32 682); the annual average registered rate was 36.22/100 000, the highest in 2018 (52.90/100 000), and the registration rate showed an increasing trend. Meanwhile, a similar trend of registration rate was observed among smear-positive or other types of students. The spatialtemporal heterogeneity was found that the "high-high" clustering patterns of smear-positive or other types were aggregated in Bijie City. Six spatialtemporal clusters with statistically significant (all P<0.001) were detected among smear-positive or other cases, respectively. Conclusions: Upward trend with spatial- temporal clusters of PTB cases reported in students from Guizhou Province from 2011 to 2020. Surveillance should be strengthened for high school students, and regular screening should be conducted in high-risk areas to control the source of infection and reduce the risk of transmission.

Multilevel resistive random access memory achieved by MoO3/Hf/MoO3stack and its application in tunable high-pass filter

In this work, the multilevel resistive random access memories (RRAMs) have been achieved by using the structure of Pt/MoO₃/Hf/MoO₃/Pt with four stable resistance states. The devices show good retention property of each state (>10⁴s) and large memory window (>10⁴). The simulation and experimental study reveal that the resistive switching mechanism is ascribed to combination of the conductive filament in the stack of MoO₃/Hf next to the top electrode and redox reaction at the interface of Hf/MoO₃next to bottom electrode. The fitting results of current-voltage characteristics under low sweep voltage indicate that the conduction of HRSs is dominated by the Poole-Frenkel emission and that of LRS is governed by the Ohmic conduction. Based on the RRAM, the tunable high-pass filter (HPF) with configurable filtering characteristics has been realized. The gain-frequency characteristics of the programmable HPF show that the filter has high resolution and wide programming range, demonstrating the viability of the multilevel RRAMs for future spiking neural network and shrinking the programmable filters with low power consumption.

Effects of hypoxia on proliferation and osteogenic differentiation of periodontal ligament stem cells: an in vitro and in vivo study

Changes in oxygen concentration may influence various innate characteristics of stem cells. The effects of varying oxygen concentration on human periodontal ligament stem cells (HPDLSCs) has not been explored, particularly under hypoxia-related conditions. First, HPDLSCs were cultured from the periodontium of human teeth using the outgrowth method. STRO-1 and CD146 expression of HPDLSCs was investigated by flow cytometry. To detect the multilineage differentiation capacities of HPDLSCs, osteogenic-like and adipogenic-like states were induced in cells. Next, HPDLSCs (passage 3) were exposed to normal oxygen (21% O2) or hypoxia (2% O2) conditions for 7 days and cell proliferation was evaluated. After culture in osteogenic medium for 7 days, osteoblastic differentiation was evaluated by semi-quantitative reverse transcription-polymerase chain reaction analysis to detect 3 osteoblastic markers: core-binding factor a 1/runt-related transcription factor 2, osteocalcin, and osteopontin. In addition, each cell group was incubated with a hydroxyapatite/tricalcium phosphate carrier and transplanted subcutaneously into the back of immunocompromised mice to investigate transplantation differences in vivo. HPDLSCs were isolated, cultured, and successfully identified. After exposure of HPDLSCs to hypoxia for 7 days, the proliferation rate was increased and showed higher osteogenic differentiation potential compared to control cells. After 12 weeks of transplantation, hypoxia-treated HPDLSCs differentiated into osteoblast-like cells that formed bone-like structures. These results suggest that oxygen concentrations affect various aspects of HPDLSC physiology and that hypoxia enhances osteogenic differentiation both in vivo and in vitro. Oxygen concentration may be a critical parameter for HPDLSCs during expansion and differentiation.

Symbiosis of Mycoplasma hominis in Trichomonas vaginalis may link metronidazole resistance in vitro

Fourteen of 28 Trichomonas vaginalis isolates collected from patients in Guangzhou, China from 2003 to 2004 were found to be naturally infected with Mycoplasma hominis, as determined by PCR using specific primers. In vitro metronidazole sensitivity assay of the 28 isolates revealed four displaying low susceptibility [minimum lethal concentration (MLC)= approximately 13-25 microg/ml] and another four displaying high resistance (MLC=50-100 microg/ml). The overwhelming majority of these resistant isolates (7/8) were mycoplasma-infected. The mean of MLCs of mycoplasma-infected isolates is approximately 10-fold higher than the mean of noninfected isolates (p=0.029). Sequence analyses of PCR-amplified small subunit-large subunit rRNA interspacer regions (ITS1/5.8S/ITS2) revealed that 23 of the 28 samples are identical, the remaining five being separable into two groups, each with a single point mutation. These internal transcribed spacer sequence variants are associated neither with mycoplasma infection nor with drug resistance. In contrast, random amplified polymorphic DNA analyses of DNAs using 10 different primers showed that the drug-resistant isolates are clustered together in association with mycoplasma infection, albeit more loosely. Taken together, the results obtained from this study suggest that in vitro metronidazole resistance of T. vaginalis is related to mycoplasma infection of this protozoan.

A point mutation in the albumin gene in a Chinese patient with familial dysalbuminemic hyperthyroxinemia

Familial dysalbuminemic hyperthyroxinemia (FDH) is an autosomal dominant disorder characterized by euthyroid hyperthyroxinemia. However, FDH has not been reported in Chinese or African patients. Here, we report the first case of FDH in a Chinese patient. A 69-year-old Chinese man was found to have increased serum total T(4) concentrations (198-242nmol/l; normal range 58-148nmol/l) and free T(4) concentrations (>58pmol/l; T(4) analog method, normal range 9-28pmol/l). Serum total T(3) and TSH concentrations were normal. The patient was misdiagnosed as hyperthyroid and was later suspected to have a TSH-producing tumor by the finding of a pituitary microadenoma, which was eventually proven to be a non-functional pituitary 'incidentaloma'. Electrophoretic analysis of the patient's serum proteins demonstrated enhanced albumin binding of [(125)I]T(4). Serum free T(4) concentrations were normal (16-19pmol/l, normal range 9-26pmol/l) when a two-step method was used. Direct sequencing of the albumin gene showed a guanine to adenosine transition in the second nucleotide of codon 218, resulting in a substitution of histidine (CAC) for the normal arginine (CGC) in one of the two alleles in the patient. The point mutation was further confirmed by HphI digestion of exon 7 of the albumin gene. The patient's son was not affected. Our studies demonstrated that the point mutation of the albumin gene in a Chinese patient with FDH was similar to that found in western white families, but differed from that in a Japanese family in whom a guanine to cytosine transition at the same position was found.

Escape from the acute Wolff-Chaikoff effect is associated with a decrease in thyroid sodium/iodide symporter messenger ribonucleic acid and protein

In 1948, Wolff and Chaikoff reported that organic binding of iodide in the thyroid was decreased when plasma iodide levels were elevated (acute Wolff-Chaikoff effect), and that adaptation or escape from the acute effect occurred in approximately 2 days, in the presence of continued high plasma iodide concentrations. We later demonstrated that the escape is attributable to a decrease in iodide transport into the thyroid, lowering the intrathyroidal iodine content below a critical inhibitory threshold and allowing organification of iodide to resume. We have now measured the rat thyroid sodium/iodide symporter (NIS) messenger RNA (mRNA) and protein levels, in response to both chronic and acute iodide excess, in an attempt to determine the mechanism responsible for the decreased iodide transport. Rats were given 0.05% NaI in their drinking water for 1 and 6 days in the chronic experiments, and a single 2000-microg dose of NaI i.p. in the acute experiments. Serum was collected for iodine and hormone measurements, and thyroids were frozen for subsequent measurement of NIS, TSH receptor, thyroid peroxidase (TPO), thyroglobulin, and cyclophilin mRNAs (by Northern blotting) as well as NIS protein (by Western blotting). Serum T4 and T3 concentrations were significantly decreased at 1 day in the chronic experiments and returned to normal at 6 days, and were unchanged in the acute experiments. Serum TSH levels were unchanged in both paradigms. Both NIS mRNA and protein were decreased at 1 and 6 days after chronic iodide ingestion. NIS mRNA was decreased at 6 and 24 h after acute iodide administration, whereas NIS protein was decreased only at 24 h. TPO mRNA was decreased at 6 days of chronic iodide ingestion and 24 h after acute iodide administration. There were no iodide-induced changes in TSH receptor and thyroglobulin mRNAs. These data suggest that iodide administration decreases both NIS mRNA and protein expression, by a mechanism that is likely to be, at least in part, transcriptional. Our findings support the hypothesis that the escape from the acute Wolff-Chaikoff effect is caused by a decrease in NIS, with a resultant decreased iodide transport into the thyroid. The observed decrease in TPO mRNA may contribute to the iodine-induced hypothyroidism that is common in patients with Hashimoto's thyroiditis.

Restoration of cyclic adenosine monophosphate-stimulated chloride channel activity in human cystic fibrosis tracheobronchial submucosal gland cells by adenovirus-mediated and cationic lipid-mediated gene transfer

In human airways, the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) is predominantly expressed in serous cells of the tracheobronchial glands. Despite considerable evidence that submucosal glands are important contributors to the pathophysiology of CF lung disease, most attempts at CFTR gene transfer have primarily targeted airway surface epithelial cells. In this study, we systematically evaluated CFTR gene transfer into cultures of immortalized CF human tracheobronchial submucosal gland (6CFSMEO) cells using adenovirus and cationic lipid vectors. We found that the efficiency of adenovirus-mediated gene transfer was comparable in 6CFSMEO and CFT1 cells (a surface airway epithelial cell line isolated from a subject with CF). So was the ranking order of adenovirus vectors containing different enhancers/promoters (CMV >> E1a approximately phosphoglycerokinase), as determined by both X-Gal staining and quantitative measurement of beta-galactosidase activity. Further, we provide the first demonstration that cationic lipids mediate efficient gene transfer into 6CFSMEO cells in vitro. The transfection efficiency at optimal conditions was higher in 6CFSMEO than in CFT1 cells. Finally, either infection with adenoviral vectors or transfection with cationic lipid:plasmid DNA complexes encoding CFTR significantly increased chloride (Cl-) permeability, as assessed using the 6-methoxy-N-(3-sulfopropyl)-quinolinium (SPQ) fluorescence assay, indicating restoration of functional CFTR Cl- channel activity. These data show that although the mechanisms of transfection may be different between the two cell types, 6CFSMEO cells are as susceptible as CFT1 cells to transfection by adenoviral and cationic-lipid gene transfer vectors.

Effects of iodine repletion on thyroid morphology in iodine and/or selenium deficient rat term fetuses, pups and mothers

It has been suggested that selenium deficiency aggravates the iodine-induced thyroid inflammation and necrosis in iodine-deficient Wistar rats and possibly in man. Studies were carried out to determine whether large amounts of iodine given to iodine-deficient pregnant Sprague-Dawley rats with or without selenium deficiency would induce inflammation and necrosis in their term fetal thyroids. Iodine deficiency was induced in the dams by a low iodine diet or perchlorate in the drinking water and iodine excess was achieved by iodinated drinking water during pregnancy or daily subcutaneous injections of iodine from days 20 to 22 of pregnancy, 1 day after perchlorate was discontinued. Studies were also carried out in 30-day-old pups whose nursing mothers were iodine-deficient (perchlorate) with or without selenium deficiency from conception onward. The administration of iodine restored the morphologic changes in the thyroid induced by iodine deficiency, irrespective of selenium status, toward normal without inflammatory changes or necrosis. Possible explanations for these unexpected findings are discussed.

Ammonium persulfate: a new and safe method for measuring urinary iodine by ammonium persulfate oxidation

The chloric acid method is most commonly used to obtain accurate and reproducible measurements of iodine and removes interfering substances. Unfortunately, chloric acid is a potential hazard requiring an explosion proof hood among other precautions. We have developed a simple, convenient, and economic method for measuring urinary iodine using 1 mol/L ammonium persulfate, a non-explosive, non-hazardous chemical, as the oxidizing reagent. The oxidation procedure can be completed in 30 minutes at a temperature of 91-95 degrees C. The iodine in the urine is then measured by a modification of the traditional colorimetric method of Sandell-Kolthoff. 110 urine samples collected from a mixed population of healthy males and females, ranging in age from 6 to 79 years and living in the United States were analyzed for iodine content by two methods: the proposed ammonium persulfate method and the chloric acid method. The ammonium persulfate method has an intra assay CV of 9.1% at 0.42 +/- 0.04 micromol/L (mean +/- SD), 7.8% at 1.46 +/- 0.11 micromol/L and 4.0% at 3.54 +/- 0.14 micromol/L. The inter assay CV is 10.2% at 0.46 +/- 0.05 micromol/L and 7.9% at 3.27 +/- 0.26 micromol/L. Recovery of iodine added to urine in vitro was 107%, 94% and 97% for 0.42 micromol/L, 0.77 micromol/L and 3.64 micromol/L, respectively. The lower limit of detectability was 0.0034 microgI. Values for iodine in 110 urines measured by the reference chloric acid method ranged from 0.06 to 8.03 micromol/L and by the ammonium persulfate method from 0.05 to 7.4 micromol/L. The persulfate method (y) correlated extremely closely with the reference chloric acid method (x) by the Pearson correlation (y = 0.923x + 0.810 micromol/L, and r = 0.994, Syx = 1.841). In conclusion a new, safe, simple method for measuring urinary iodine is described which uses ammonium persulfate as the oxidizing agent for the removal of interfering substances.

Circulating iodide concentrations during and after pregnancy

Early, indirect studies suggested that an important aspect of thyroid economy during pregnancy was a decline in plasma or serum inorganic iodide (PII) concentrations, but there is little information concerning circulating iodide concentrations as assessed by direct measurement. The present study was undertaken to determine the relationship between gestation and serum iodide concentrations as assessed by direct measurement of PII. PII concentrations, urinary iodide levels, and other parameters of thyroid economy were measured during the first, second, and third trimesters and after delivery in 16 women. Mean serum T4 concentrations were significantly higher in all 3 trimesters than those after delivery. Serum free T4 index concentrations were significantly higher in the first trimester than during later periods of gestation or after delivery, but serum TSH concentrations were not depressed in the first trimester. Serum thyroglobulin concentrations were similar during pregnancy and after delivery. There was wide variability in PII and urinary iodide concentrations during and after pregnancy, but there was no trend for PII concentrations to be depressed during pregnancy. Pregnancy, at least in iodine-sufficient regions, does not have an important influence on circulating concentrations of iodide.

The effect of recombinant human thyrotropin (rhTSH) on thyroid function in mice and rats

The vast majority of studies to determine the biological activity of recombinant human thyrotropin (rhTSH) have been carried out in the mouse. We have recently reported that 0.1 mg of rhTSH IM (one-ninth the dose given in thyroid cancer patients) given to normal subjects elicits a brisk rise in serum thyroxine (T4), triiodothyronine (T3), and thyroglobulin (Tg) concentrations. In contrast, in initial studies in the rat, a low dose of rhTSH failed to increase serum T4 or T3 concentrations. The present study was, therefore, carried out to determine the biological activity of rhTSH in euthyroid and in T3-treated, TSH-suppressed rats and mice. Doses of rhTSH based on body weight were used and resulted in similar serum human thyrotropin (hTSH) concentrations in the two species. Euthyroid and TSH-suppressed mice responded briskly to rhTSH administration. In contrast, serum T4 did not increase after rhTSH administration in euthyroid rats. In TSH-suppressed rats, the increase in serum T4 was similar to that observed in TSH suppressed mice. These observations suggest that rhTSH more readily displaces endogenous TSH from the mouse than from the rat thyroid TSH receptor, because equal responses were observed when endogenous TSH was suppressed.

Efficiency of cationic lipid-mediated transfection of polarized and differentiated airway epithelial cells in vitro and in vivo

Systematic analysis of a large number of different cationic lipids has led to the identification of novel structures (GL-67) and formulations of cationic lipid:plasmid DNA (pDNA) complexes that facilitate high levels of gene expression in lungs of mice. However, despite significant improvement in gene transfer activity, we show here that the efficiency of GL-67-mediated gene transduction of intact airway epithelia is still relatively low. Administration of GL-67:pCF1-CFTR (encoding the cystic fibrosis transmembrane conductance regulator) complexes into the nasal epithelium of cystic fibrosis (CF) transgenic mice resulted only in marginal correction of the ion transport defects. Measurements of nasal potential differences (PD) showed no correction of the sodium (Na+) transport defect, and only partial restitution of the chloride (Cl-) transport defect was achieved in a small proportion of the animals after perfusion of the nasal epithelium with the complexes. Furthermore, in contrast to results obtained following instillation of GL-67:pDNA complexes into the lungs of mice, perfusion of GL-67:pDNA into the nasal epithelium resulted only in a moderate enhancement of gene transduction activity relative to that attained with naked pDNA alone. To determine the basis for this low efficiency of transfection, a series of studies was conducted to identify some of the barriers governing cationic lipid-mediated gene transfer to the airway epithelium. We show here that the transfection activity of GL-67 was affected by the polarization, differentiation, and proliferative state of the cells. Diminished transfection activity was observed with nonmitotic, highly polarized and differentiated airway epithelial cells. This observed reduction in gene expression with nonmitotic cells was determined to be due in part to inefficient nuclear translocation of the pDNA from the cytoplasm. Together these data indicate that much improvement in the ability of cationic lipids to transfect polarized and differentiated airway epithelial cells is a necessary prerequisite for effective cationic lipid-mediated gene therapy of airway diseases such as CF.

Partial restoration of cAMP-stimulated CFTR chloride channel activity in DeltaF508 cells by deoxyspergualin

Deletion of the codon encoding phenylalanine 508 (DeltaF508) is the most common mutation in cystic fibrosis (CF) and results in a trafficking defect. Mutant DeltaF508-CF transmembrane conductance regulator (CFTR) protein retains functional activity, but the nascent protein is recognized as abnormal and, in consequence, is retained in the endoplasmic reticulum (ER) and degraded. It has been proposed that this retention in the ER is mediated, at least in part, by the cellular chaperones heat shock protein (HSP) 70 and calnexin. We have investigated the ability of deoxyspergualin (DSG), a compound known to compete effectively for binding with HSP70 and HSP90, to promote trafficking of DeltaF508-CFTR to the cell membrane. We show that DSG treatment of immortalized human CF epithelial cells (DeltaF508) and cells expressing recombinant DeltaF508-CFTR partially restored cAMP-stimulated CFTR Cl- channel activity at the plasma membrane. Although there are several possible explanations for these results, one simple interpretation is that DSG may have altered the interaction between DeltaF508-CFTR and its associated chaperones. If this is correct, agents capable of altering the normal functioning of cellular chaperones may provide yet another means of restoring CFTR Cl- channel activity to CF subjects harboring this class of mutations.

Dehydroepiandrosterone sulfate does not prevent spontaneous and iodine-induced lymphocytic thyroiditis and diabetes mellitus in the BB/Wor rat

Chronic feeding of dehydroepiandrosterone (DHEA) and its sulfated metabolite, dehydroepiandrosterone sulfate (DHEAS), has previously been reported to decrease hyperglycemia, obesity, cancer, and autoantibody generation in a number of animal models and to increase muscle mass and physiological and psychological well-being in elderly humans, although these latter studies remain controversial. The present study was carried out to determine whether large amounts of DHEAS given orally would prevent the occurrence of spontaneous and iodine-induced autoimmune lymphocytic thyroiditis (LT) and/or spontaneous insulin-dependent diabetes mellitus (DM) in male and female BB/Wor rats. DHEAS was administered by gavage (44 mg/rat/day) or in the chow (133 mg/rat/day) to LT- and DM-prone rats from 30 to 120 days of life; some of these rats also received iodine in the drinking water to enhance the incidence and intensity of LT. Onset of DM requiring protamine zinc insulin and its maintenance dose were assessed. Rats were killed at 90 or 120 days of age and blood, thyroid, adrenals, pancreases, testes, and ovaries were removed. Serum glucose, DHEA, DHEAS, thyroxine (T4), tri-iodothyronine (T3) and thyrotropin (TSH) concentrations were measured in all rats in both experiments. Serum DHEAS concentrations were 10-fold higher in the rats given the steroid by gavage or in the diet compared with levels in control rats. DHEAS administered over a prolonged period of time had no significant effect on body weight, incidence and severity of DM, incidence and intensity of spontaneous and iodine-induced LT, and thyroid, pancreas and testes weights but did significantly decrease adrenal and ovarian weights. Serum T4, T3, and TSH concentrations were similar in control and DHEAS-treated rats. In conclusion, DHEAS did not prevent the occurrence of iodine-induced or spontaneous autoimmune LT or spontaneous DM in the BB/Wor rat, at variance with its reported immunosuppressive effects in other animal models.

The effect of nicotine on thyroid function in rats

Very recently, it has been reported that subclinical hypothyroidism is more severe and peripheral markers of hypothyroidism are more pronounced in women with subclinical or overt hypothyroidism who smoke. Increased concentrations of the known goitrogen thiocyanate, generated from cigarette smoke, have been the major explanation for the decreased thyroid function in these women but do not explain the reported increased peripheral markers of hypothyroidism. There are no data on the effect of the other major product of cigarettes, nicotine, on thyroid function in vivo. The present studies were therefore performed to determine the effects of large doses of nicotine infused for 7 days on thyroid function, outer-ring 5'deiodinase activity (5'D-I), and hepatic malic enzyme activity (a measure of thyroid hormone action) in euthyroid, subclinically hypothyroid (hemithyroidectomized), and L-thyroxine (L-T4)-treated thyroidectomized rats. Nicotine infusion had no effect on serum T4, triiodothyronine (T3), thyrotropin (TSH), and cholesterol concentrations, intrathyroidal metabolism of 125I, liver and kidney 5'D-I activity, and hepatic malic enzyme activity in euthyroid and subclinically hypothyroid rats. Nicotine administration also did not affect serum T3, TSH, or cholesterol concentrations, liver and kidney 5'D-I activity, and hepatic malic enzyme activity in L-T4-treated thyroidectomized rats. These studies provide strong evidence that nicotine is not responsible for the observed adverse effects of smoking on the thyroid in humans.

Fluorine intake of a Tibetan population

Measurements of food consumption of randomly selected families and fluorine levels in food and beverages were used to calculate the fluorine intake of Tibetan people living in nomadic or semi-nomadic areas of the region and regularly consuming brick tea both as a beverage and in food. The fluorine intake of these groups (children 5.49-7.62 mg day; adults 10.43-14.48 mg/day) was much higher than that of members of a Han population living in the region (children 1.44 mg/day; adults 2.54 mg/day). The amounts of fluorine consumed by the Tibetan inhabitants are at least twice the WHO suggested limit (2 mg/day). Tea plants are rich in fluorine, and the highest levels are found in older leaves which are used to make brick tea. We conclude that brick tea is the major source of fluorine intake by the Tibetan population studied.

Comparison of the effects of propylthiouracil and selenium deficiency on T3 production in the rat

Selenium deficiency and propylthiouracil (PTU) treatment both decrease hepatic type I T4 5'-deiodinase activity (5'D-I), which is considered to be an important regulator of the serum T3 derived from peripheral T4 to T3 conversion (T3 neogenesis). The effects of PTU treatment or a selenium-deficient diet on T4 and T3 kinetics were compared in thyroid-ablated rats infused with stable T4 to determine whether PTU treatment is a more potent inhibitor of T3 neogenesis than selenium deficiency and to compare the degree of inhibition of T3 production with the degree of inhibition of 5'D-I. PTU treatment and selenium deficiency (Se-) did not affect the T3 MCR (control, 46.0 +/- 2.5; PTU, 41.7 +/- 2.8; Se-, 41.1 +/- 4.0 ml/h.100 g BW), but did reduce serum T3 concentrations by 29% and 25%, respectively (control, 58.7 +/- 2.6; PTU, 41.5 +/- 1.0; Se-, 43.9 +/- 2.7 ng/dl; P < 0.01 for PTU or Se- vs. control) and the T3 production rate by 35% and 32%, respectively (control, 26.6 +/- 1.0; PTU, 17.3 +/- 2.0; Se-, 18.0 +/- 1.9 ng/h.100 g BW; P < 0.01 for PTU or Se- vs. Control). PTU treatment and selenium deficiency significantly increased serum T4 concentrations by 36% and 32%, respectively, due to a decrease in T4 MCR (control, 1.4 +/- 0.1; PTU, 1.1 +/- 0.1; Se-, 1.1 +/- 0.04 ml/h.100 g BW; P < 0.05 for PTU or Se- vs. control). Assuming that the concentration of T4 available for T3 neogenesis is proportional to the serum T4 concentration, the increase in serum T4 concentrations caused by PTU treatment or Se- would probably have proportionally increased the rate of T3 neogenesis. Based on these considerations, the apparent decrease in T3 neogenesis in the PTU-treated animals was 52%. This is less than the 79% and 67% inhibition of 5'D-I noted, respectively, in the liver and kidneys of these rats. Similarly, the apparent decrease in T3 neogenesis in the Se- rats was 48%, again less than the 85% and 64% inhibition of 5'D-I in their liver and kidneys, respectively. These studies suggest that PTU and Se- have similar effects on T3 neogenesis. The more potent effects of these treatments on liver and kidney 5'D-I activities than on T3 neogenesis suggest that the activities of these enzymes in these tissues are not the only important determinants of the serum T3 that is derived from nonthyroidal sources.

Serum iodothyronine concentrations in intestinally decontaminated rats treated with a 5'-deiodinase type I inhibitor 6-anilino-2-thiouracil

Enteric bacteria have been postulated to have a role in thyroid economy by promoting the hydrolysis of thyroid hormone conjugates of biliary origin, thus permitting the absorption and recycling of thyroxine (T4) and triiodothyronine (T3). An enterohepatic circulation of T3 might be more pronounced under conditions in which type I iodothyronine deiodinase activity (5'D-I) is inhibited, because this augments the accumulation of T3 sulfate conjugates in bile. This potential of increased gut reabsorption of T3 might explain, at least in part, the failure of serum T3 values to decrease appreciably when marked reductions in peripheral 5'D-I activity are induced by selenium deficiency or 6-anilino-2-thiouracil (ATU) administration. Thus, studies were performed to determine the effect of intestinal decontamination, in the absence and in the presence of 5'D-I inhibition, on plasma T4 and T3 concentrations. Groups of adult male rats received either enteric antibiotics or no antibiotics for 12 days and then, in half of the rats in each group, treatment for 10 days with ATU, a 5'D-I inhibitor that does not affect thyroid hormone synthesis. The activity of intestinal arylsulfatase and arylsulfotransferase, enzymes that catalyze hydrolysis of thyroid hormone conjugates, was reduced markedly by approximately 87% in rats that received antibiotics, regardless of whether or not they also received ATU. The ATU treatment markedly inhibited liver 5'D-I activity in antibiotic-treated as well as in non-antibiotic-treated rats (control = 399 +/- 32 U/mg protein (mean +/- SEM); ATU = 152 +/- 17: antibiotics = 351 +/- 29; antibiotics + ATU = 130 +/- 10; p < 0.01) and significantly increased plasma T4 and T3 sulfate (T4S, T3S) concentrations (control: T4S = 2.8 +/- 0.4 and T3S = 6.7 +/- 1.3 ng/dl; ATU: T4S = 6.2 +/- 1.4 and T3S = 10.6 +/- 2.1 ng/dl; antibiotics: T4S = 1.8 +/- 0.2 and T3S = 3.6 +/- 1.0 ng/dl; antibiotics + ATU: T4S = 6.8 +/- 0.7 and T3S = 9.7 +/- 1.8 ng/dl; p < 0.05). The ATU treatment was associated with a significant increase in plasma T4 and rT3 concentrations but did not affect plasma T3 concentrations, and intestinal decontamination did not alter these ATU-associated effects on circulating thyroid hormones. These results suggest that anaerobic enteric bacteria in the rat do not have an important role in recycling of thyroid hormones, either under normal conditions or in circumstances where 5'D-I activity is markedly reduced, and that increased gut absorption of T3 from T3S cannot explain the near-normal serum T3 values found when peripheral 5'D-I activity is markedly decreased.

Ammonium persulfate: a safe alternative oxidizing reagent for measuring urinary iodine

The chloric acid method is most commonly used to obtain accurate and reproducible measurements of iodine and remove interfering substances. Unfortunately chloric acid is a potential hazard, requiring an explosion-proof hood, among other precautions. We have developed a simple, convenient, and economic method for measuring urinary iodine by using 1 mol/L ammonium persulfate, a nonexplosive, nonhazardous chemical, as the oxidizing reagent. The oxidation procedure can be completed in 30 min at a temperature of 91-95 degrees C. The iodine in the urine is then measured by a modification of the traditional colorimetric method of Sandell and Kolthoff. Urine samples (110) collected from a mixed population of healthy males and females, ranging in age from 6 to 79 years and living in the US, were analyzed for urine iodine content by two methods: the proposed ammonium persulfate method and the chloric acid method. The ammonium persulfate method has an intraassay CV of 9.1% at 0.42 +/- 0.04 micromol/L (mean +/- SD), 7.8% at 1.46 +/- 0.11 micromol/L, and 4.0% at 3.54 +/- 0.14 micromol/L. The interassay CV is 10.2% at 0.46 +/- 0.05 micromol/L, and 7.9% at 3.27 +/- 0.26 micromol/L. Recovery of iodine added to urine in vitro was 107%, 94%, and 97% for 0.42 micromol/L, 0.77 micromol/L and 3.64 micromol/L, respectively. The lower limit of detectability was 0.0034 microgram of iodine. Values for iodine in 110 urines measured by the reference chloric acid method ranged from 0.06 to 8.03 micromol/L and by the ammonium persulfate method from 0.05 to 7.4 micromol/L. The persulfate method (y) correlated extremely closely with the reference chloric acid method (x) by the Pearson correlation (y = 0.923x + 0.810 micromol/L, and r = 0.994, Sy/x = 1.841).

Ammonium persulfate: a safe alternative oxidizing reagent for measuring urinary iodine

The chloric acid method is most commonly used to obtain accurate and reproducible measurements of iodine and remove interfering substances. Unfortunately chloric acid is a potential hazard, requiring an explosion-proof hood, among other precautions. We have developed a simple, convenient, and economic method for measuring urinary iodine by using 1 mol/L ammonium persulfate, a nonexplosive, nonhazardous chemical, as the oxidizing reagent. The oxidation procedure can be completed in 30 min at a temperature of 91-95 degrees C. The iodine in the urine is then measured by a modification of the traditional colorimetric method of Sandell and Kolthoff. Urine samples (110) collected from a mixed population of healthy males and females, ranging in age from 6 to 79 years and living in the US, were analyzed for urine iodine content by two methods: the proposed ammonium persulfate method and the chloric acid method. The ammonium persulfate method has an intraassay CV of 9.1% at 0.42 +/- 0.04 micromol/L (mean +/- SD), 7.8% at 1.46 +/- 0.11 micromol/L, and 4.0% at 3.54 +/- 0.14 micromol/L. The interassay CV is 10.2% at 0.46 +/- 0.05 micromol/L, and 7.9% at 3.27 +/- 0.26 micromol/L. Recovery of iodine added to urine in vitro was 107%, 94%, and 97% for 0.42 micromol/L, 0.77 micromol/L and 3.64 micromol/L, respectively. The lower limit of detectability was 0.0034 microgram of iodine. Values for iodine in 110 urines measured by the reference chloric acid method ranged from 0.06 to 8.03 micromol/L and by the ammonium persulfate method from 0.05 to 7.4 micromol/L. The persulfate method (y) correlated extremely closely with the reference chloric acid method (x) by the Pearson correlation (y = 0.923x + 0.810 micromol/L, and r = 0.994, Sy/x = 1.841).

Delivery of purified, functional CFTR to epithelial cells in vitro using influenza hemagglutinin

To assess the feasibility of protein replacement as a potential therapy for cystic fibrosis, we have evaluated the ability of influenza hemagglutinin (HA) to mediate the delivery of purified cystic fibrosis transmembrane conductance regulator (CFTR) to recipient cells in vitro. CFTR was purified from both CHO cells and Sf9 cells and reconstituted into two different types of vesicular delivery vehicles. In one, CFTR and HA were co-reconstituted into the same lipid vesicle. After binding to the cell surface, delivery of CFTR to the recipient cell was achieved by a transient, low-pH activation of the fusion activity of HA. A second delivery strategy used HA virosomes together with purified CFTR that had been reconstituted into vesicles containing gangliosides, a receptor for HA. After binding of the HA virosomes and CFTR-containing vesicles to the recipient cells, delivery to the plasma membrane again was achieved by a transient pH drop. Delivery of functional CFTR was assessed using the SPQ fluorescence assay. Functional CFTR was detected in a fraction (> 20%) of the recipient cells using this assay. Quantitative binding and fusion assays using radiolabeled virosomes and lipid vesicles showed that on the order of 1,000 of the added CFTR-containing vesicles bound to each C127 cell under the conditions of our delivery protocols. However, only a fraction of these vesicles fused and delivered CFTR to the cell plasma membrane. The two delivery strategies were found to be approximately equivalent in their ability to deliver active CFTR, and there were no significant differences between deliveries using purified CFTR from either cell source. These feasibility studies suggest that purified CFTR can be delivered to a recipient cell in a functional form and therefore represent a significant step in establishing the concept of protein replacement as a therapy for cystic fibrosis.

Purinoceptor P2U identification and function in human intrahepatic biliary epithelial cell lines

The mechanisms that regulate ion and fluid transport by the human intrahepatic bile duct have not been well defined. Human intrahepatic biliary cell lines that we have developed were used to identify and characterize purinoceptors based on increases in intracellular calcium in response to ATP and other nucleotides. Intracellular free calcium was measured in cell suspensions using the fluorescent probe Fura-2 and a fluorescence spectrophotometer. Halide efflux was measured in single cells using fluorescence microscopy and the fluorescent probe SPQ. Intracellular calcium increases equivalently in response to ATP and UTP, peaking, then diminishing to a new, elevated baseline. The peak elevation of calcium is the result of both the release of intracellular stores of calcium and the influx of extracellular calcium. The purinoceptor P2U-subtype was identified based on the potency rank order of ATP-analogues. Halide efflux increases with P2U-purinoceptor stimulation which is consistent with the opening of a Ca(2+)-sensitive Cl- channel. The physiological significance of P2U-purinoceptor activation and its effect on the ionic content and flow rate of bile remains to be determined.

Functional activation of the cystic fibrosis trafficking mutant delta F508-CFTR by overexpression

The most common mutation in the gene associated with cystic fibrosis (CF) causes deletion of phenylalanine at residue 508 (delta F508) of the gene product called CFTR. This mutation results in the synthesis of a variant CFTR protein that is defective in its ability to traffic to the plasma membrane. Because earlier studies showed delta F508-CFTR retains significant phosphorylation-regulated chloride (Cl-) channel activity, processes capable of restoring the mislocalized delta F508-CFTR to the correct cellular destination may have therapeutic benefit. Here we report one such process that involves overexpression of the mutant protein and appears to result in the escape of a small amount of delta F508-CFTR to the plasma membrane. In recombinant cells where expression of delta F508-CFTR is controlled by the metallothionein promoter, this effect can be brought about by treatment with sodium butyrate. Although cAMP-activated Cl- channel activity could also be detected in immortalized human airway epithelial cells homozygous for the delta F508 mutation at the single cell level, treatment with butyrate did not generate a measurable cAMP-stimulated Cl- current in polarized monolayers of primary CF airway epithelia. However, the observation that overexpression can effect the presence of recombinant delta F508-CFTR at the plasma membrane suggests that perhaps other butyrate-like compounds that are more potent and more specific for the promoter of the CF gene may be efficacious in alleviating the Cl- channel defect associated with CF.

Correction of the cystic fibrosis defect by gene complementation in human intrahepatic biliary epithelial cell lines

BACKGROUND/AIMS

Hepatobiliary disease is the second most common cause of mortality in patients with cystic fibrosis (CF). In the liver, only the intrahepatic biliary epithelial (IBE) cells express cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. The aim of this study was to determine whether human CF-derived IBE cells can be infected with adenovirus and the CF phenotype complemented.

METHODS

IBE cells were isolated from 2 patients with CF and immortalized using retrovirus transduction of SV40 large T antigen. Immortalized cells were infected with the adenovirus vector Ad2/CFTR2 and assayed 2-31 days postinfection for cyclic adenosine monophosphate (cAMP)-induced halide efflux. Halide efflux was measured in single cells using fluorescence microscopy and the fluorescent probe 6-methoxy-N-(3-sulfopropyl)-quinolinium.

RESULTS

CF-derived IBE cell lines express biliary specific markers and express no cAMP-inducible halide efflux. Following infection with the adenovirus vector Ad2/CFTR2, a cAMP-induced halide efflux was observed for 31 days, although the number of responsive cells decreased with time.

CONCLUSIONS

Human CF-IBE cells can be infected by adenovirus and the defective CFTR complemented. The loss of responsive cells with time could be due to loss of construct and/or a reduced growth of cells that are overexpressing CFTR. These CF-IBE cell lines offer an opportunity to determine the mechanisms responsible for hepatobiliary disease in the patients with CF.

Tumor necrosis factor-alpha decreases thyrotropin-induced 5'-deiodinase activity in FRTL-5 thyroid cells

Tumor necrosis factor-alpha (TNF-alpha) exerts various effects on many cell types. Acute administration of TNF-alpha to rats decrease hepatic 5'-deiodinase activity (5'D-I) and TNF-alpha has been implicated in the pathogenesis of the low triiodothyronine syndrome in non-thyroidal illness in humans. The thyroid, liver and kidney are rich in 5'D-I. Unlike hepatic and renal 5'D-I, thyroid 5'D-I is regulated by thyrotropin. We have investigated the effects of TNF-alpha on 5'D-I in FRTL-5 cells, a cultured rat thyroid follicular cell line. Tumor necrosis factor-alpha did not significantly affect basal 5'D-I but thyrotropin markedly increased 5'D-I (p < 0.001). This TSH-induced increase in 5'D-I was attenuated by TNF-alpha in a dose-dependent manner (p < 0.001). Enzyme kinetic analysis demonstrated that thyrotropin increased 5'D-I by increasing Vmax (p < 0.01) without significantly affecting Km. Likewise, TNF-alpha decreased the thyrotropin-induced 5'D-I by decreasing Vmax (p < 0.05) but not Km. The effect of TNF-alpha on thyrotropin-induced 5'D-I in FRTL-5 cells is probably mediated through post-thyrotropin-induced generation of cyclic adenosine monophosphate (cAMP) because TNF-alpha inhibited both dibutyryl cAMP (p < 0.001) and forskolin (p < 0.001)-induced increases in 5'D-I without affecting cAMP generation stimulated by thyrotropin. In conclusion, we have demonstrated that TNF-alpha inhibits thyrotropin-induced 5'D-I activity in FRTL-5 cells by pathways distal to the generation of cAMP and that TNF-alpha may play a role in the modulation of the production of triiodothyronine by the thyroid gland. (ABSTRACT TRUNCATED AT 250 WORDS)

The postnatal serum 3,5,3'-triiodothyronine (T3) surge in the rat is largely independent of extrathyroidal 5'-deiodination of thyroxine to T3

In the rat, selenium deficiency causes a near-complete loss of the selenoenzyme type I 5'-deiodinase (5'D-I), resulting in a marked decrease in hepatic T4 to T3 conversion. In adult rats, serum T4 concentrations are consistently increased, whereas serum T3 and rT3 concentrations are unaffected or slightly decreased and increased, respectively. In rat fetuses near term, serum T4 and rT3 concentrations are not affected by selenium deficiency. We have now studied the effect of selenium deficiency on thyroid function in the neonatal rat. Weanling female rats were fed either a selenium-supplemented or a selenium-deficient diet for 4 weeks before mating and then throughout gestation and lactation. Neonatal rats were killed at 7, 14, 21, and 28 days. Selenium deficiency was confirmed by a more than 89% decrease in liver 5'D-I activity in mothers and pups. Selenium deficiency resulted in significant increases in serum T4 concentrations in 3- and 4-week-old pups. In contrast, selenium deficiency led to a striking increase in serum rT3 concentrations. The normal postnatal serum T3 surge was not affected by selenium deficiency at any age. In 2- and 4-week-old selenium-deficient pups obtained from a second litter from the same mothers, liver 5'D-I activity was markedly decreased, but thyroid 5'D-I activity was not affected. The increased serum rT3 and, less so, T4 concentrations observed in selenium-deficient pups were associated with a significant decrease in brain 5'D-II activity in 14- and 28-day-old pups and in brown adipose tissue 5'D-II activity in 14-day-old pups. In conclusion, the present study demonstrates that the increase in serum T4 concentrations consistently observed in selenium-deficient adult rats occurs only after the second week of life. The normal physiological postnatal 12-fold increase in serum T3 concentrations observed in selenium-deficient pups despite the marked decreases in liver 5'D-I and brain and brown adipose tissue 5'D-II activities suggests that T4 to T3 conversion by peripheral tissues may not be a major source of T3 in the neonate. In contrast, the thyroid gland, whose 5'D-I activity is not affected by selenium deficiency, is probably the principal source of circulating T3 in the neonate. Finally, the early and marked increase in serum rT3 concentrations observed in selenium-deficient pups suggests that liver 5'D-I is important in rT3 deiodination.

Gene expression and serum thyroxine-binding globulin are regulated by adrenal status and corticosterone in the rat

Supraphysiological doses of glucocorticoids reduce serum T4-binding globulin (TBG) concentrations when administered to human subjects. Studies were performed in rats to determine if glucocorticoid administration alters serum TBG in another species, if circulating concentrations of glucocorticoids tonically affect serum TBG concentrations, and if changes in TBG production are likely to be a cause of the glucocorticoid-induced changes in serum TBG concentrations that are observed in humans. The serum TBG-binding capacity was 14.9 +/- 2.3 nmol/liter in adrenalectomized male rats compared to 6.6 +/- 1.0 nmol/liter in intact male rats and 4.8 +/- 0.9 nmol/liter in adrenalectomized male rats that received corticosterone in a dose equal to or less than the replacement dose, as assessed by thymus weight (P < 0.01 for serum TBG in adrenalectomized vs. intact or adrenalectomized corticosterone-treated groups). Hepatic TBG mRNA content, as assessed by polymerase chain reaction amplification and expressed as a ratio of beta-actin mRNA content, was 0.10 +/- 0.03 density units in intact male rats, 0.59 +/- 0.17 density units in adrenalectomized male rats, and 0.05 +/- 0.02 density units in adrenalectomized corticosterone-treated male rats (P < 0.03 for adrenalectomized vs. intact or adrenalectomized corticosterone-treated rats). Adrenalectomy increased the serum TBG-binding capacity in female rats (intact female rats, 13.9 +/- 1.0 nmol/liter; adrenalectomized female rats, 39.0 +/- 6.4 nmol/liter; P < 0.01). These studies indicate that serum TBG is tonically down-regulated by adrenal glucocorticoids, because corticosterone decreases the TBG production rate, probably at the level of transcription. This effect is similar to that described for corticosterone-binding globulin, but differs from that for many proteins of the serine protease inhibitor family that are related to TBG.

Placental 5-deiodinase activity and fetal thyroid hormone economy are unaffected by selenium deficiency in the rat

In adult male rats, selenium deficiency results in a near complete loss in the selenoprotein 5'-deiodinase in the liver, resulting in decreased peripheral deiodination of thyroxine (T4) and increased serum T4 concentrations. Serum 3,5,3'-triiodothyronine concentrations are normal or slightly decreased, and serum 3,3',5'-triiodothyronine concentrations are normal or slightly increased in selenium-deficient rats. We now report the effects of selenium deficiency on maternal and fetal thyroid hormone economy and on placental 5-deiodinase activity in the rat. Weanling female rats were fed either a selenium-deficient or selenium-supplemented diet for 4 wk before mating and then throughout gestation. Rats were killed at 21 d of gestation. Selenium deficiency was confirmed by a 95 and 94% decrease in glutathione peroxidase and a 84 and 56% decrease in liver type I outer ring 5' deiodinase activity in the mother and the fetus, respectively. In contrast to the increase in circulating T4 observed in selenium-deficient male and nonpregnant female adult rats, serum T4 was not affected by selenium deficiency in pregnant rats, but there was a 3-fold increase in serum 3,3',5'-triiodothyronine concentrations associated with a 70% decrease in maternal brain type II outer ring 5' deiodinase activity. Maternal serum 3,5,3'-triiodothyronine concentrations were decreased by 21%. Placental 5-deiodinase activity was unaffected by selenium deficiency. In the fetus, serum T4, 3,3',5'-triiodothyronine, and TSH concentrations were not affected by selenium deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of in vivo administration of recombinant acidic fibroblast growth factor on thyroid function in the rat: induction of colloid goiter

We have recently demonstrated that the iv administration of 0.6-60 micrograms/kg.day of acidic fibroblast growth factor (acidic FGF) increases thyroid weight in male and female rats. Interestingly, measurement of serum TSH and thyroid hormones in rats treated with 6 micrograms/kg.day acidic FGF for 30 days revealed only a slight increase in serum T4 and reverse T3 concentrations. Since thyroid function was only examined 24 h after the 30th daily treatment, we performed a series of experiments to evaluate the effects of acidic FGF on thyroid function following single and 6 multiple injections of acidic FGF. There was a small increase in the serum TSH concentrations at 2, 4, 8, and 24 h after a single high dose iv injection of acidic FGF (60 micrograms/kg). In contrast, serum T3 concentrations were slightly decreased at 2, 4, and 8 h after acidic FGF administration. There was no effect of a single injection of acidic FGF on serum T4, reverse T3, or thyroglobulin concentrations. After 6 days of treatment, there was a 34% increase in the thyroid weights of rats treated with acidic FGF. Analysis of serum hormones revealed a slight increase in serum TSH, T3, and T4 concentrations in acidic FGF-treated rats, but no change in serum reverse T3 or thyroglobulin concentrations. There was no effect of acidic FGF administration on thyroid radioiodine uptake, the intrathyroidal metabolism of radioiodine, or the relative amounts of thyroidal thyroglobulin or peroxidase messenger RNAs, or on liver 5'-deiodinase activity. In hypophysectomized rats, with no detectable levels of serum TSH, acidic FGF failed to increase thyroid weight. These data suggest that FGFs may participate with TSH in the regulation of thyroid weight and colloid accumulation, and that autocrine or paracrine growth factors may be involved in the pathogenesis of colloid goiter.

1,25-Dihydroxycholecalciferol modulates 3H-thymidine incorporation in FRTL5 cells

1,25-dihydroxycholecalciferol (1,25(OH)2D3) possesses proliferation and differentiation modulating effects in many cell types in vitro. We studied the effect of 1,25(OH)2D3 on 3H-thymidine incorporation in FRTL5 cells, a cultured rat thyroid follicular cell line. 1,25(OH)2D3 alone at 10(-11) and 10(-9) M exerted no effect on 3H-thymidine incorporation. However, at 10(-7) M, 1,25(OH)2D3 slightly enhanced 3H-thymidine incorporation. In the presence of 5% calf serum, 1,25(OH)2D3 increased 3H-thymidine incorporation induced by calf serum in a dose-dependent manner. 1,25(OH)2D3 also enhanced 3H-thymidine incorporation induced by PMA, an extrinsic stimulator of protein kinase C, without directly affecting PMA-induced protein kinase C translocation. In contrast to the stimulatory effects of 1,25(OH)2D3 on the calf serum and PMA-induced 3H-thymidine incorporation, 1,25(OH)2D3 inhibited the increase in 3H-thymidine incorporation induced by TSH in a dose-dependent manner. This effect of 1,25(OH)2D3 on TSH-induced 3H-thymidine incorporation may be, in part, due to post-cAMP pathways since 1,25(OH)2D3 also inhibited the increase in 3H-thymidine incorporation induced by Bu2cAMP without affecting the TSH-induced increase in cAMP. The stimulatory effect of insulin on 3H-thymidine incorporation, a cAMP-independent process, was also inhibited by 1,25(OH)2D3. We conclude that 1,25(OH)2D3 affects 3H-thymidine incorporation in FRTL5 cells raising the possibility of a physiologic role for 1,25(OH)2D3 in the growth and function of thyroid follicular cells.

Role of transthyretin in the transport of thyroxine from the blood to the choroid plexus, the cerebrospinal fluid, and the brain

T4 is bound to transthyretin (TTR; 75%) and albumin (Alb; 25%) in rat serum and only to TTR in cerebrospinal fluid (CSF). In addition to the liver, TTR is synthesized in large amounts in the choroid plexus and then secreted into the CSF, suggesting that serum T4 could be transported to the CSF and brain via the choroid plexus. We determined whether serum T4 bound to TTR is transported into the choroid plexus and CSF. N-Bromoacetyl-L-[125I]T4, a derivative of T4 that binds covalently to TTR, was used as the affinity label for the T4-binding site on TTR. Rats were injected with [125I]T4, acetyl-[125I]T4 covalently bound to human TTR ([125I]T4Ac.human hTTR), or acetyl-[125I]T4 covalently bound to human Alb ([125I]T4Ac.hAlb). The quantities of [125I]T4Ac.hTTR and [125I]T4Ac.hAlb present in the choroid plexus, CSF, and brain 90 min later were barely detectable. In contrast, [125I]T4 injected as the unbound form accumulated in the choroid plexus and CSF to levels 6-11 times higher than with [125I]T4Ac.hTTR (P less than 0.005). We then used a synthetic flavonoid (EMD) that competitively inhibits binding of T4 to serum TTR and transiently increases serum free T4 to determine the role of choroid plexus TTR and CSF TTR in the transport of T4 from serum to brain. Rats were given 110 microCi [125I]T4 15 min after the injection of vehicle, a low (0.3 mumol/100 g BW) or high dose of EMD (2.0 mumol/100 g BW). Rats were killed 60 min later. In serum, the percentage of [125I]T4 bound to TTR decreased and free T4 increased similarly in the low and high dose EMD-treated rats. In contrast, the percentage of [125I]T4 bound to TTR in choroid plexus and, subsequently, CSF was significantly decreased in rats given the high dose of EMD, but was not affected by the low dose of EMD, suggesting that in high doses, EMD crossed from serum to choroid plexus and CSF and occupied TTR-binding sites for T4. There was a significant decrease (P less than 0.05) in the percentage of injected [125I]T4 in the high dose vs. the low dose EMD-treated rats in total choroid plexus (61%), 1 ml CSF (94%), and 1 g cerebral cortex (46%) and cerebellum (46%).(ABSTRACT TRUNCATED AT 400 WORDS)

Iodine content of rat thyroglobulin affects its antigenicity in inducing lymphocytic thyroiditis in the BB/Wor rat

The BB/Wor rat develops spontaneous insulin dependent diabetes mellitus (DM) and lymphocytic thyroiditis (LT). We have recently demonstrated that immunization of BB/Wor rats with allogeneic thyroglobulin (Tg) induces LT at an early age. The incidence of spontaneous and Tg induced LT is extremely variable among different BB/Wor sublines. It has been shown that high iodine diet significantly increases the incidence of spontaneous lymphocytic thyroiditis (LT) and low iodine diet significantly decreases the incidence of LT in genetically predisposed BB/Wor rats. Recent studies on thyroglobulin (Tg) induced LT in chicken and mouse have shown that iodine rich Tg is far more antigenic than Tg with a low iodine content, suggesting that a high iodine diet increases the immunogenicity of Tg molecule. In order to determine whether the extent of Tg iodination would affect its immunogenicity in the BB/Wor rats, the current study was carried out. Normal iodine Tg (NTg) or low iodine Tg (LTg) was obtained from thyroids of rats that were placed on regular diet or regular diet plus 0.5% methimazole, respectively. 120 rats from the NB (highly susceptible) and BB (low susceptible) sublines were randomized in three groups. Immunization was carried out with a 1:1 emulsion of complete Freund's adjuvant (CFA) and LTg, NTg (0.6 mg/rat) or saline at 30 and 37 days of age. Since spontaneous LT rarely occurs before age 75 days, rats were sacrificed at age 65 days to specifically study Tg induced LT. Immunization with NTg induced LT in 31% of the NB rats, but not in the BB subline. LTg did not induce LT in either subline.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid alteration in circulating free thyroxine modulates pituitary type II 5' deiodinase and basal thyrotropin secretion in the rat

TSH secretion is decreased by both T4 and T3. This negative feedback control of TSH secretion has been correlated with an increase in pituitary nuclear T3 content, and it is not clear whether T4 exerts its effect directly on the thyrotroph or after its deiodination to T3. However, levels of the pituitary enzyme catalyzing T4 to T3 conversion, 5'D-II, are decreased in the presence of an increased amount of T4. Thus, it is unclear why the thyrotroph would have a mechanism for modulating the production of T3, if T3 is, in fact, the sole bioactive signal providing negative feedback inhibition. To examine this apparent paradox, we administered EMD 21388, a compound which inhibits the binding of T4 to transthyretin resulting in a rapid increase in circulating free T4 levels, to rats pretreated with radiolabeled T4 and T3. We observed increases in pituitary and liver T4 content of greater than 150%, without increases in the respective tissue T3 contents. The EMD 21388-treated rats also exhibited a 25% decrease in pituitary 5'D-II activity (103.8 +/- 15.8 fmol 125I released.mg protein-1.h-1, vs. control, 137.4 +/- 15.9, mean +/- SE), as did rats treated with sodium salicylate, another compound that inhibits T4-TTR binding (100.8 +/- 7.1). TSH levels significantly decreased 2 h after the administration of EMD 21388. These data demonstrate that despite a T4-mediated decrease in pituitary 5'D-II activity, an increase in T4 independently decreases TSH secretion.

Effect of the cardiac inotropic drug, OPC 8212, on pituitary-thyroid function in the rat

3,4-Dihydro-6-[4-(3,4-dimethoxybenzoyl)-1 piperaznyl]-2(1H)-quinolinone (OPC 8212) is a new synthetic quinolinone with potent cardiac inotropic action in man. Long term oral administration of OPC induces goiter and thyroid tumor formation in rats, associated with decreases in serum T4 and increases in serum TSH concentrations. Studies were carried out to explore the mechanisms responsible for these drug induced abnormalities. OPC 8212, administered for 1 week at doses of 500 and 2000 mg/kg.day mixed with the diet, resulted in an increase in thyroid weight, a decrease in circulating T4 and free T4 concentrations and an increase in serum TSH concentrations. OPC decreased the 5'-deiodinase (5'-D) activity in liver homogenates and increased the 5'-D activity in pituitary homogenates, consistent with hypothyroidism. OPC 8212 did not affect thyroid iodine metabolism and hormone synthesis or the binding of T4 to serum binding proteins. The hepatic uptake of 125 I-T4 4 h after T4 administration was significantly increased in OPC 8212 treated rats. The biliary excretion of administered 125 I-T4 was increased in OPC 8212-treated rats and most of the increase was due to an increase in the excretion of T4-glucuronide. Hepatic T4-glucuronyltransferase activity measured in vitro in OPC 8212 treated rats was increased as compared to that of controls. It is concluded that the effect of OPC 8212 on lowering serum T4 with a compensatory rise in TSH leading to goiter formation is due to a drug-induced increase in hepatic T4 disposal. The induction of T4-glucuronyl-transferase appears to play an important role in the increased biliary excretion of T4 in OPC 8212-treated rats.

Thyroglobulin induced lymphocytic thyroiditis in two sublines of BB/Wor rats

The BB/Wor rat develops spontaneous insulin dependent diabetes mellitus (DM) and lymphocytic thyroiditis (LT). We have recently demonstrated that although the incidence of spontaneous DM is relatively constant among different inbred BB/Wor sublines the incidence of LT is extremely variable. Experimental LT can be induced in some animal species by immunization with thyroglobulin (Tg). The differences in susceptibility of Tg induced LT between a high incidence LT subline (NB) and a low incidence subline (BB) were determined after immunization with Tg obtained from Wistar rat thyroids. Immunization was accomplished using 0.6 mg Tg in complete Freund's adjuvant (FA) or FA alone at 30 and 37 days. Since spontaneous LT rarely occurs before age 75 days, rats were sacrificed at age 65 days to specifically study Tg induced LT. Immunization with Tg induced LT in the NB subline but not in the BB subline. Anti-Tg antibody (Ab) titers, T4-Ab and T3-Ab were all increased in both Tg immunized sublines but were significantly higher in Tg immunized NB rats than in Tg immunized BB rats. The increase in T4-Ab or T3-Ab resulted in factitiously low serum T4 and T3 values when a single Ab technique with polyethylene glycol (PEG) precipitation was used in the RIA. There was a dissociation in the incidence of Tg induced LT and Ab production. Although Tg immunization failed to induce LT in the BB subline, anti-Tg Ab were significantly elevated as well as both T4-Ab and T3-Ab, suggesting that anti-Tg Ab titers per se are not tightly correlated with the occurrence of LT.(ABSTRACT TRUNCATED AT 250 WORDS)

Gender-related differences of serum thyroxine-binding proteins in the rat

Because little information is available, studies were performed to determine the relationship between gender and sex steroid status on serum T4 binding proteins in the rat. The binding capacity of serum thyroxine-binding globulin was greater in female rats than in male rats (27 +/- 1.3 vs 18.0 +/- 1.3 nmol/l, p less than 0.01) and in fasted female rats than in fasted male rats (64.4 +/- 2.6 vs 30.8 +/- 2.7 nmol/l, p less than 0.01). The binding capacity of serum transthyretin was lower in female rats than in male rats (2.1 +/- 0.1 vs 3.1 +/- 0.1 mumol/l, p less than 0.01). Neither ovariectomy or orchidectomy affected the binding capacity of serum thyroxine-binding globulin and it was not increased in ovariectomized rats treated with estrogen. Orchidectomy did not cause a decrease in the binding capacity of serum transthyretin and testosterone administration did not increase it. In contrast, ovariectomy caused an increase in the binding capacity of serum transthyretin (Intact = 2.2 +/- 0.1 vs ovariectomized = 2.8 +/- 0.1 mumol/l, p less than 0.01) and estrogen administration caused a decrease (ovariectomized = 2.8 +/- 0.1 vs ovariectomized + E2 = 1.9 +/- 0.1 mumol/l, p less than 0.05). The results indicate that the binding capacity of serum thyroxine-binding globulin is higher in female rats than in male rats but this difference is not due to differences in the secretion of gonadal hormones. The binding capacity of transthyretin is lower in female rats than in male rats. This is probably due to the higher circulating levels of estrogen in the female compared to the male.

Flavonoid administration immediately displaces thyroxine (T4) from serum transthyretin, increases serum free T4, and decreases serum thyrotropin in the rat

Naturally occurring and synthetic plant flavonoids, such as EMD 21388, are potent inhibitors of thyroid hormone 5'-deiodinase (5'-D) in vitro, but not when given in vivo, since they are tightly bound by serum transthyretin (TTR). EMD 21388 also inhibits the binding of T4 to human, dog, and rat serum TTR in vitro and when administered to rats in vivo. In the present studies the administration of EMD 21388 inhibited the binding of T4 to TTR within 3 min, resulting in a decrease in the serum T4 concentration, an increase in the percentage of serum free T4 assessed by equilibrium dialysis, and an increase in the serum total free T4 concentration. Depending upon the dose of EMD 21388 employed, the serum total free T4 concentration was either elevated for at least 60 min or transiently elevated, returning to normal values by 60 min. Although the total serum T3 concentration was decreased and the percent free T3 increased, these changes were modest, and the serum free T3 concentrations remained normal after EMD 21388 administration. The transient elevations of serum free T4 concentrations 10 and 20 min after the administration of 0.3 mumol EMD 21388/100 g BW resulted in a significant decrease in the serum TSH concentration at 60 min. These observations strongly suggest that the serum free T4 concentration and not T4 bound to serum TTR is biologically available to the pituitary to regulate TSH secretion and/or synthesis. The administration of EMD 21388, which rapidly increases the serum free T4, but not the serum free T3, concentration, will now permit studies of the effect(s) of endogenously elevated serum free T4 concentrations, rather than those after the administration of pharmacological quantities of T3 and T4, on various aspects of the biosynthesis and release of pituitary TSH.

Rapid effects of the flavonoid EMD 21388 on serum thyroid hormone binding and thyrotropin regulation in the rat

Naturally occurring and synthetic flavonoids are potent inhibitors of thyroid hormone 5'-deiodination and binding to human serum transthyretin (TTR) in vitro. We now describe the inhibitory effect of the most potent flavonoid, 3-methyl-4',6-dihydroxy-3',5'-dibromo-flavone (EMD 21388), on the serum protein binding of T4 and T3 and subsequent alterations of pituitary-thyroid function in the rat. Eight to 10 mumol/liter EMD 21388 added to pooled rat serum completely displaced [125I]T4 or [125I]T3 binding from TTR, the major thyroid hormone-binding protein in the rat, and markedly increased the percentages of free T4 and T3, measured by equilibrium dialysis. One to 4 h after the ip administration of 2 mumol EMD 21388/100 g BW to euthyroid rats, [125I]T4 and [125I]T3 binding to TTR decreased, serum T4 and T3 concentrations decreased, and the percentages of free T4 and free T3 increased. No changes were observed in the free T4 and free T3 concentrations. Serum TSH concentrations decreased at 1 h and were very low thereafter. EMD 21388 administration did not affect the elevated serum TSH concentrations in hypothyroid rats, strongly suggesting that the flavonoid does not directly affect TSH secretion. No changes were observed in hepatic type I 5'-deiodinase in euthyroid rats and pituitary type I and type II 5'-deiodinase in euthyroid and hypothyroid rats after EMD 21388 administration. We conclude that the ip administration of EMD 21388 to euthyroid rats inhibits T4 and T3 binding to TTR, with subsequent increases in the percentages of free T4 and free T3 and decreased serum T4 and T3 concentrations. The decrease in the serum TSH concentration was possibly due to transcient increases in the serum free T4 and/or free T3 concentrations, resulting in increased pituitary thyroid hormone content.

Thyroid hormone antibodies and Hashimoto's thyroiditis in mongrel dogs

Abnormally elevated serum T3 concentrations measured by RIA were observed in 19 clinically euthyroid or hypothyroid mongrel dogs. The serum T4 concentrations in these sera were low, normal, or high. Measurement of the intensity of thyroid hormone binding to serum proteins was determined by equilibrium dialysis. A marked decrease in the percent free T3 was observed in these abnormal sera. Polyacrylamide gel electrophoresis, pH 7.4, of normal dog serum enriched with tracer 125I-labeled thyroid hormones demonstrated binding of [125I]T4 to transthyretin, thyroid hormone-binding globulin, and albumin and of [125I]T3 primarily to thyroid hormone-binding globulin. In all abnormal sera, polyacrylamide gel electrophoresis demonstrated strikingly higher binding of T3 to immunoglobulin (Ig). Eleven of 16 abnormal sera had minimal to moderate binding of T4 to Ig. The percent free T4 was lower only in dogs whose sera demonstrated markedly increased binding of T4 to Ig. All abnormal sera tested had positive antithyroglobulin antibodies, consistent with the diagnosis of autoimmune lymphocytic thyroiditis. As in humans, antibodies to thyroid hormones in dogs are more common in the presence of Hashimoto's thyroiditis and should be considered when elevated serum thyroid hormone concentrations are observed in the absence of clinical thyrotoxicosis. When an antibody to only one thyroid hormone is present, a marked discrepancy in the serum concentrations of T3 and T4 will be observed.

Thyroxine binding to serum thyronine-binding globulin in thyroidectomized adult and normal neonatal rats

The amount of tracer [125I]T4 bound to serum thyronine-binding globulin (TBG) was measured by polyacrylamide gel electrophoresis in adult thyroidectomized (TX) rats and normal 1-day to 4-week-old rat puts. Thyroidectomy was associated with the appearance of significant amounts of [125I]T4 binding to serum TBG in lean rats, but not in obese Zucker rats. Treatment of the TX rats in vivo with replacement doses of T4 prevented this increase in TBG binding, but enrichment of serum from TX rats with T4 did not. Significant amounts of tracer [125I]T4 binding to TBG was present in serum from 1- to 3-week-old normal rat pups, but not in 1-day- or 4-week-old pups. There were significantly higher levels of TBG binding of [125I]T4 in serum from 2-week-old rat pups raised in litters of 16 pups compared to those raised in litters of 4 pups. All manipulations that result in the appearance of TBG in rat serum also result in either weight loss or a slowing in the rate of growth, suggesting that the appearance of TBG in rat serum has a nutritional component. This possibility is further supported by the observations that increases in TBG binding of [125I]T4 are not found in obese Zucker rats fed a low protein-high carbohydrate diet for 14 days or fasted for 7 days, or after thyroidectomy, perhaps owing to the large stores of fuel in the obese rat.

Effects of amiodarone and desethylamiodarone on pituitary deiodinase activity and thyrotropin secretion in the rat

The effect of acute administration of amiodarone, its major metabolite desethylamiodarone and iodine in an amount equal to that contained in amiodarone on serum thyroid hormone and thyrotropin (TSH) concentrations and hepatic and pituitary 5' deiodination of thyroxine (T4) in the euthyroid and hypothyroid rat was evaluated. Amiodarone, desethylamiodarone and iodine all caused a decrease in serum T4 and triiodothyronine (T3) concentrations in euthyroid rats, while serum TSH concentrations and pituitary and hepatic 5' deiodinase activities were decreased only in the amiodarone and desethylamiodarone-treated animals. Serum TSH was increased in the iodine treated rats. Amiodarone, but not iodine, decreased serum T3 and TSH concentrations and pituitary and hepatic 5' deiodinase activities in hypothyroid rats. Inhibition of hepatic 5' deiodinase activity was also observed by the addition of amiodarone in vitro in the absence of dithiothreitol (DTT) but not in the presence of DTT. The decrease in the serum T4 concentration observed with amiodarone and desethylamiodarone administration is probably secondary to the inhibitory effect of iodine released from the drugs on thyroidal T4 synthesis and secretion. Iodine inhibition of thyroidal T3 synthesis and secretion, decreased T4 substrate for a peripheral generation of T3 and inhibition of T4 to T3 conversion all contribute to the decrease in serum T3 observed. The decrease in the serum TSH concentration, despite low serum T4 and T3 concentrations and inhibition of pituitary 5' deiodinase, suggest that amiodarone may function as a thyroid hormone agonist in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

A new class of propylthiouracil analogs: comparison of 5'-deiodinase inhibition and antithyroid activity

After in vivo administration, propylthiouracil (PTU) inhibits not only thyroid iodide uptake and organification, but also T4 5'-deiodinase activity in most peripheral organs. The present report describes the effects of some previously untested 6-substituted 2-thiouracil derivatives on in vivo and in vitro iodide uptake and organification, and on T4 5'-deiodinase activity in liver and pituitary homogenates. When added to homogenates, many analogs were as potent or more potent than PTU in inhibiting hepatic T4 5'-deiodinase activity. Three derivatives, 6-anilino-2-thiouracil (A compound), 6-(p-ethylanilino)2-thiouracil (B compound), and 6-(p-n-butylanilino) 2-thiouracil (C compound), which were among the most potent inhibitors of hepatic T4 5'-deiodinase, when added in vitro inhibited T4 5'-deiodinase activity in liver homogenates after in vivo administration. When added to pituitary homogenates prepared from hypothyroid rats, these compounds also significantly inhibited pituitary T4 5'-deiodinase activity. In a concentration of 1 mM in the presence of 20 mM dithiothreitol, the percent inhibition of pituitary T4 5'-deiodinase activity was 19.7 +/- 7.4 (mean +/- SE), 34.0 +/- 3.2, 47.3 +/- 3.1, and 89.0 +/- 1.0 for PTU and the A, B, and C compounds, respectively (P less than 0.05 for all groups vs. one another and vehicle). Despite their ability to inhibit hepatic T4 5'-deiodinase activity, none of the 13 analogs tested altered thyroid iodide uptake or organification after administration of 0.1 mg/rat. PTU, in the same dose, inhibited thyroid iodide uptake by 78.2 +/- 2.4% (P less than 0.001) and thyroid iodide organification by 36.4 +/- 7.3% (P less than 0.01). Furthermore, the A, B, and C compounds did not inhibit thyroid iodide uptake or iodide organification when administered in higher doses of 5, 5, and 1 mg/rat, respectively. In contrast to these in vivo results, the A, B, and C compounds were more potent than PTU in inhibiting iodide organification in a purified thyroid peroxidase system and in porcine thyroid slices. The concentrations causing 50% inhibition of iodide organification in the purified thyroid peroxidase system were 30, 7, 8, and 14 microM for PTU and the A, B, and C compounds, respectively. However, PTU was far more potent in inhibiting iodide organification in intact incubated thyroid lobes compared to the A, B, and C compounds.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro immunoreactivity to propylthiouracil, methimazole, and carbimazole in patients with Graves' disease: a possible cause of antithyroid drug-induced agranulocytosis

Studies of in vitro immunoreactivity to propylthiouracil (PTU), methimazole (MMI), and carbimazole (CARB), as assessed by peripheral blood lymphocyte transformation and 2 antibody tests, were carried out in 12 patients with Graves' hyperthyroidism who had developed agranulocytosis during treatment with PTU (11 patients) or CARB (1 patient) from 1 week to 10 yr earlier. Significant lymphocyte transformation responses to antithyroid drugs (stimulation indices greater than mean +/- 2 SD for normal subjects) were found in 5 of 6 patients tested, in 1 patient to PTU only, in 3 patients to MMI only, and in 1 patient to both PTU and MMI, but in none of 10 patients currently being treated with PTU who did not develop agranulocytosis. Circulating antibodies causing neutrophil agglutination in the presence of antithyroid drugs were demonstrated, using the indirect Coombs test, in 5 of 7 patients tested, in 2 patients to PTU only, in 3 patients to CARB only and in 1 patient (the only one tested with MMI) to PTU and MMI. Lymphocyte transformation and antibody tests to PTU were both carried out in 6 patients. Of these, both tests were positive in one patient, both negative in 3 patients, and 1 negative and 1 positive in 2 patients. In the 1 patient in whom both tests were carried out with CARB (patient 3), tests were negative, whereas in the 1 patient in whom both tests were carried out with MMI (patient 3), 1 test was positive, whereas the other was negative. Thus, in patients in whom both tests were carried out using the same drug, correlation between lymphocyte transformation responses and the detection of neutrophil antibodies was found in 5 of 6 cases. Antibodies reactive with neutrophils were also detected in 2 of the 5 patients tested using an enzyme-linked immunosorbent assay. In this test antibodies to PTU or MMI were not demonstrated. Possible mechanisms for the neutrophil depression in relation to these findings are discussed. It is concluded that patients with Graves' disease may be prone to develop this complication of antithyroid drug therapy because of underlying immunological abnormalities.

Hepatic conversion of thyroxine to triiodothyronine in obese and lean Zucker rats

The in vitro conversion of thyroxine (T4) to triiodothyronine (T3) was studied in liver homogenates from fed and fasted lean and obese Zucker rats. T3 generation was decreased in fed young (2 month) obese rats as compared to values in fed lean controls. This was not corrected by the addition of dithiothreitol (DTT), suggesting a deficiency in 5'-deiodinase activity in young obese rats. Both lean and obese 2 month old rats responded to a 2 day fast by decreasing hepatic T3 generation as is always observed in other strains of rats. The hepatic conversion rate was not decreased in older (5 month) fed obese rats when compared to age-matched lean controls. Hepatic conversion of T4 to T3 was markedly decreased in 5 month old lean Zucker rats fasted for 4 days. In contrast, a 4 day fast had no effect on the hepatic conversion rate in the 5 month old obese rats. The hepatic conversion rate was assessed in 5 month old obese rats fasted for up to 28 days and hepatic conversion still did not decrease. This paradoxical response of the 5 month old obese rat may provide a new model to further evaluate the control of hepatic T3 generation from T4.

The effects of propylthiouracil, iodothyronines, and other agents on thyroid hormone metabolism in human placenta

Human and rat placental homogenates contain inner ring deiodinase activity (PT4ase) towards T4 and T3. This activity may decrease the transfer of T4 and T3 across the placenta and influence thyroid hormone disposal in the fetal circulation. Data are now presented on human PT4ase in subcellular fractions, the Km of human PT4ase, and the effects of drugs and other compounds on human and rat PT4ase. The specific activity (nanograms of rT3 produced per min/mg protein) of each fraction of human placenta was as follows: nuclear, 0.07; mitochondrial, 0.15; lysosomal, 0.19; microsomal, 1.30; and cytosol, 0.01. The apparent Michaelis-Menton (Km) for PT4ase in human placental microsomes was 1.2 X 10(-7) M. T3, 3,3'-diiodothyronine, iopanoic acid, iodoacetic acid, diamide, and propranolol all exhibited dose-dependent inhibition of human and rat PT4ase when tested in the presence of 10 mM dithiothreitol (DTT). Propylthiouracil did not inhibit PT4ase at 10 mM DTT, but when the DTT concentration was lowered to 0.25 mM, up to 71% inhibition was noted. Many drugs, as noted in other organs with respect to outer and inner ring iodothyronine deiodinases, inhibited human PT4ase. These studies may be relevant to the practice of administering propylthiouracil, propranolol, and iopanoic acid to pregnant women.

Inner ring deiodination of thyroxine and 3,5,3'-triiodothyronine by human fetal membranes

Indirect evidence, based on injection of thyroxine (T4) into the amniotic cavity of humans, and maternal thyroidectomy in the rat, suggests that fetal membranes might be capable of converting T4 to 3,3',5'-triiodothyronine (rT3) by virtue of inner ring iodothyronine deiodinase activity. The present study was undertaken to provide direct evidence that human fetal membranes contain inner ring iodothyronine deiodinase activity directed toward T4 and 3,5,3'-triiodothyronine (T3). Homogenates of human fetal membranes were incubated with 125I-labeled T4, rT3, and T3, and with stable T4. Conversion of 125[I]-T4 to 125[I]-rT3 was noted in chorion and amnion. 125I-T3 was converted to 125[I]-3,3'-diiodothyronine (T2) in chorion and amnion. 125[I]-rT3 was stable in fetal membranes under the incubation conditions employed. Time-, temperature-, pH-, and protein content-dependent conversion of stable T4 to rT3 was found in fetal membranes. Iodothyronine metabolism did not occur in the absence of dithiothreitol. These studies indicate that human fetal membranes contain an inner ring deiodinase enzyme. Because of its intimate contact with the amniotic cavity, this enzyme may generate a portion of the rT3 found in amniotic fluid.

Ontogenesis of placental inner ring thyroxine deiodinase and amniotic fluid 3,3',5'-triiodothyronine concentration in the rat

Human and rat placentae contain enzymatic activity which converts T4 to rT3 and T3 to 3,3'-diiodothyronine and 3'-monoiodothyronine. This study presents data on the ontogeny of this inner ring iodothyronine deiodinase activity (P-T4ase) in rat placenta. P-T4ase was measured by quantitating the conversion of T4 to rT3 in 700 x g supernatants of placental homogenates. Groups of rats were mated to permit the dams to be killed on the same day, on days 12, 14, 16, 18, and 20 of gestation. Sufficient placental tissue was obtained to measure P-T4ase on all but the 12th day of gestation. The highest level of P-T4ase was observed on day 16. P-T4ase on days 14, 18, and 20 was 52%, 77%, and 41%, respectively, of that observed on day 16 (P less than 0.01, day 16 vs. all other days). Amniotic fluid rT3 concentrations were highest on day 18 and were 61% and 64%, respectively, of that observed on day 18 (P less than 0.01, days 16 and 20 vs, day 18). At 20 days, maternal serum T4 concentrations were significantly lower (P less than 0.01) than on days 14, 16, or 18. A brief period of maternal hypothyroidism (4 or 9 days before the time that the animals were killed on day 20 of gestation) did not significantly alter P-T4ase. These studies indicate that there are age-dependent changes in placental inner ring deiodinase activity in the rat. Amniotic fluid rT3 concentrations may reflect these changes. Brief reductions in maternal serum T4 concentrations do not account for changes in placental inner ring deiodinase activity. These studies emphasize the importance of gestational age in studies of placental inner ring iodothyronine deiodinase.

Rat placenta is an active site of inner ring deiodination of thyroxine and 3,3',5-triiodothyronine

Inner ring deiodination of L-T4 and L-T3 by rat placental homogenates resulted in the generation of rT3 from T4 and 3,3'-diiodothyronine and 3'-monoiodothyronine from T3. Dithiothreitol is required in the incubation medium. There was little or no detectable outer ring deiodination of T4 and T3. These findings suggest that placenta enzymatic inner ring monodeiodination of T4 and T3 could prevent the transplacental passage of T4 and T3 from dam to fetus. They also provide an explanation for our previous observations that fetal serum rT3 is partially dependent on maternal thyroid function.