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J R Stockigt

Publications and source records attributed to J R Stockigt.

At least 19 recordsLinked to original sources
PubMed1992

A novel variant of transthyretin (prealbumin), Thr119 to Met, associated with increased thyroxine binding.

A group of patients with prealbumin associated hyperthyroxinemia possess a common single base substitution in the fourth exon of their transthyretin gene. This cytosine to thymine substitution occurs in the codon for residue 119 and results in the predicted replacement of a threonine residue with a methionine at this position. A new NcoI restriction endonuclease cleavage site is created by the point mutation and can be detected by a rapid and simple assay based on the polymerase chain reaction. This variant transthyretin is inherited in an autosomal dominant manner and is apparently not amyloidogenic but is associated with increased thyroxine binding. As healthy heterozygous individuals have normal serum thyroxine concentrations, the hyperthyroxinemia sometimes found may not be primarily due to the variant.

Base Sequence↗
PubMed1992

Characterization of cytoplasmic T3 binding sites by adsorption to hydroxyapatite: effects of drug inhibitors of T3 and relationship to glutathione-S-transferases.

To facilitate studies of thyroid hormone (T3) binding to cytoplasmic proteins, we prepared monkey (M. fascicularis) liver cytosol (100,000g supernatant) and examined T3 binding using hydroxyapatite (HAP) separation. HAP adsorbs cytoplasmic and nuclear binding sites but not serum T4 binding proteins. Cytosol was incubated with [125I]T3 for 30 min at 4 degrees C and separated by adding an equal volume of HAP (15 g/100 mL). After a further incubation of 10 min, the HAP pellet was washed three times in buffer containing Triton X-100, 0.5%. With this method, a single class of T3 binding site was observed with Kd 15.8 +/- 1.2 nM, concentration 0.62 +/- 0.17 pmol/mg protein (n = 3, mean +/- SD). We used this assay to assess potential drug inhibitors of cytoplasmic binding and to evaluate the proposal that glutathione-S-transferases (GST) and cytoplasmic T3 binding proteins are identical. Displacement of [125I]T3 by unlabeled iodothyronines relative to T3 (100) was T4 58, Triac 7, rT3 7, Tetrac less than or equal to 1. This hierarchy indicates that this binding site is distinct from nuclear or serum binding sites. T3 binding was displaceable by nonsteroidal anti-inflammatory drugs (NSAID) and nonbile acid cholephils (NBAC). Half-inhibitory concentrations (microM, mean +/- SD, n greater than or equal to 3) were diclofenac 4.9 +/- 1.3, mefenamic acid 13.6 +/- 0.6, bromosulphthalein 45 +/- 3, iopanoic acid approximately 200. Amiodarone and furosemide were inactive up to 100 microM. No displacement was observed with cortisol or the bile acid taurocholate, up to 100 microM. Dithiothreitol, 5 mM, did not change binding affinity or capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone↗
PubMed1991

Interactions between oleic acid and drug competitors influence specific binding of thyroxine in serum.

Long chain nonesterified fatty acids and various drugs may share albumin-binding sites in common. We questioned whether serum binding of T4 could be indirectly influenced by displacement of drug competitors from these sites by nonesterified fatty acids. The influence of oleic acid on drug-induced inhibition of [125I]T4 binding was measured by equilibrium dialysis, using undiluted serum in order to avoid dilution-related artefacts. Oleic acid (1 mmol/L) alone did not inhibit serum protein binding of T4, but this concentration augmented the inhibitory effects on T4 binding of diflunisal, mefenamic acid, meclofenamic acid, and aspirin. This effect increased with increasing concentrations of mefenamic acid, meclofenamic acid, and furosemide. The T4-displacing effect of fenclofenac was not augmented by oleic acid. The mechanism of these interactions was studied by examining 1) oleic acid effects on drug binding, and 2) drug effects on oleic acid binding in undiluted serum. Increments in added oleic acid (0.5-2.0 mmol/L) progressively increased the mean unbound fractions of [14C]aspirin, [14C] diflunisal, and [14C]furosemide, but did not displace [14C]fenclofenac. At the relevant total and free drug concentrations, the inhibitory effect of oleic acid on drug binding and its influence on drug-induced displacement of T4 were concordant in the order: meclofenamic acid greater than aspirin greater than mefenamic acid greater than diflunisal greater than furosemide greater than fenclofenac. In contrast, drug-induced increases in the unbound fraction of [14C]oleic acid did not correlate with augmentation of T4 displacement. We conclude that synergistic effects of oleic acid and drugs on T4 binding result from drug displacement by oleic acid, rather than the reverse effect. Hence, substances that increase the unbound concentration of a competitor by displacing it from albumin can increase its T4-displacing potency. Interactions between various ligands may exert a greater hormone-displacing effect than the sum of each alone.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1991

The thyroid hormone analogue SKF-94901 and iodothyronine binding sites in mammalian tissues: differences in cytoplasmic binding between liver and heart.

The thyroid hormone analogue, SKF-94901 exhibits greater thyromimetic activity in the liver than in the heart. This difference in activity may reflect heterogeneity in the affinity of SKF-94901 for different forms of the T3 receptor. A difference in extranuclear transport of the analogue could also account for the different response of these two tissues. To distinguish between these possibilities we have examined the binding of SKF-94901 to membrane, cytosolic and nuclear preparations from liver and heart of the primate, Macaca fascicularis. Uptake of SKF-94901 into H4 liver cells was low. Binding of [125I]T3 to cell membrane preparations (Kd approximately 3 mumol/l), and to nuclear extracts (Kd approximately 0.2 nmol/l) was displaceable by SKF-94901 with a potency 2-5% that of T3 in each case. No significant difference was observed between liver and heart for SKF-94901 binding to membranes or nuclear extract. With cytosol, [125I]T3 binding was identical in heart (Kd, 22.7 +/- 10.4 nmol/l) and liver tissue (Kd, 30.3 +/- 11.1 nmol/l). In liver, and in cardiac cytosol after preliminary washing to remove serum, iodothyronine potency was in the order T3 greater than T4 greater than rT3. The ratio of SKF-94901 to T3 concentrations which gave 50% displacement was 15.9 +/- 6.8 in the liver; and 152.3 +/- 89.1 in the heart (p less than 0.05). The selective tissue activity of SKF-94901 may be related to a reduced affinity of the analogue for the cytosolic binding proteins in the heart, rather than a difference in affinity for various forms of the T3 receptor.

Animals↗
PubMed1990

Practical management of diabetic ketoacidosis and hyperosmolar coma.

In diabetic ketoacidosis (DKA) and particularly in hyperosmolar coma, rapid normalisation of the measured extracellular fluid abnormalities cannot be equated with optimal management. In both disorders there are complex imbalances between extra- and intracellular compartments that are best corrected in a series of rational steps, based on an understanding of pathophysiology. Fluid administration in DKA can generally be divided into three successive phases: (i) a short period of rapid isotonic saline infusion, (ii) slower infusion of isotonic saline with potassium chloride, and (iii) glucose-potassium infusion until oral food intake is well established. In severe cases, there is a definite place for judicious use of isotonic sodium bicarbonate in small amounts. While insulin infusion is desirable, intramuscular insulin remains a satisfactory alternative. Biochemical monitoring is mandatory and management must be reviewed and modified every three to four hours on the basis of the clinical and biochemical response. In the management of hyperosmolar coma, insulin and fluid therapy are more conservative, with the aim of achieving complete rehydration and normoglycaemia only after 36 to 72 hours. Pulmonary complications and the effects of tissue ischaemia, as well as thromboembolic events, remain important causes of death in both disorders. The frequent recurrences of DKA that occur in a group of psychiatrically-unstable young patients remain an unsolved problem.

Diabetic Coma↗
PubMed1989

Measurement of the unbound fraction of long chain nonesterified fatty acids (NEFA) in serum: methodological considerations.

Long-chain nonesterified fatty acids (NEFA) are extensively bound to albumin; knowledge of their unbound concentrations is important in evaluating the numerous biologic effects attributed to these compounds. We measured the unbound fraction of five long-chain NEFA in serum using the equilibrium partition of 14C-NEFA between heptane and aqueous phases. Commercial 14C-NEFA preparations gave non-linear estimates of unbound fraction with serum dilution, consistent with the presence of polar tracer impurities, but 14C-NEFA purified by alkaline ethanol extraction gave an approximately linear relationship between unbound fraction and serum dilution over a 4096-fold range of dilution, provided that pH of the aqueous phase remained stable. Mean unbound percentages were: myristic acid 0.0066, linolenic acid 0.0019, arachidonic acid 0.0017, oleic acid 0.00078 and palmitic acid 0.00061. These data suggest that some previous studies appear to have overestimated the free fraction of long-chain NEFA at physiological albumin concentrations by at least one order of magnitude.

Arachidonic Acids↗
PubMed1989

Deaths associated with diabetic ketoacidosis and hyperosmolar coma. 1973-1988.

We assessed the possibility of improvements in the management of the potentially fatal acute hyperglycaemic complications of diabetes by a review of all deaths in patients who presented to the Alfred Hospital, Melbourne, with diabetic ketoacidosis or hyperosmolar coma during the 16 years, 1973-1988. All late deaths of patients during hospitalization were included in the mortality data. In the 610 episodes of diabetic ketoacidosis (pH, 7.30 or lower) or hyperosmolar coma (osmolality, 350 mOsmol/kg or greater), only one death occurred as a result of the acute metabolic disturbance--in a patient who had suffered a cardiac arrest before admission to hospital. The over-all mortality rate was 6.2% (38 deaths). The mortality rate was 4.9% (26 deaths) for 528 episodes of diabetic ketoacidosis and 14.6% (12 deaths) for 82 episodes of hyperosmolar coma. Patients with diabetic ketoacidosis who died were older than were those who survived (64 +/- 13 years compared with 40 +/- 21 years, respectively; P less than 0.001). Mortality in patients with hyperosmolar coma did not relate to age, initial blood-glucose level or osmolality. Twelve deaths resulted from bacterial pneumonia and two deaths resulted from aspiration pneumonia. Other major causes of death were mesenteric and iliac thromboses (six cases), myocardial infarction (eight cases) and cerebral haemorrhage (two cases). Of the 26 deaths that were associated with diabetic ketoacidosis, only two deaths--as a result of aspiration pneumonia and bowel infarction, respectively--were assessed as potentially avoidable after the patient's admission to hospital. Eight of the 12 hyperosmolar-coma-associated deaths occurred in newly recognized diabetic patients in whom there were avoidable delays in diagnosis. We conclude that further improvements in outcome will be difficult to achieve, but that efforts should be directed towards the earlier diagnosis of diabetes and the earlier recognition and treatment of associated acute pulmonary and vascular complications.

Adult↗
PubMed1989

The thyroid hormone analogue SKF L-94901: nuclear occupancy and serum binding studies.

1. We studied a brominated thyroid hormone analogue, SKF L-94901, which has the potential to lower serum cholesterol without adverse cardiovascular effects. This compound is about 50% as active as tri-iodothyronine (T3) in liver nuclear receptor binding in vivo but only 1% as active in vitro and has nearly 200 times more enzyme-inducing activity in liver than in heart. Our aim was to examine the interaction of SKF L-94901 with [125I]T3 binding to the intact nuclei in whole cells, isolated nuclei and nuclear extracts of human HeLa cells and to investigate the binding of this compound to human serum. 2. Relative to thyroxine (T4), the affinity of this compound for T4-binding globulin was 0.0035%, for transthyretin 1.66% and for albumin 1.26%. Low affinity for serum proteins, with a relatively high circulating free fraction, could explain why SKF L-94901 is more potent in vivo than in vitro. 3. Human HeLa cell nuclei, isolated after whole-cell incubations, bound [125I]T3 with high affinity (Kd = 78 +/- 8 pmol/l, mean +/- SEM), which was displaceable by T3 analogues in the order Triac [( 4-(4-hydroxy-3-iodophenoxy)-3,5-di-iodophenyl]acetic acid) greater than T3 greater than T4 much greater than reverse T3. Similar high-affinity (Kd = 58 +/- 6 pmol/l, mean +/- SEM) and identical specificity was observed in high-salt (0.4 mol/l KCl) nuclear extracts. In nuclei of whole cells incubated with [125I]T3 and SKF L-94901, the analogue was 0.8% as potent as T3, whereas in experiments with nuclear extract, the analogue was 7.7% as potent as T3.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed1989

Uptake of 3,5,3'-triiodothyronine by cultured rat hepatoma cells is inhibitable by nonbile acid cholephils, diphenylhydantoin, and nonsteroidal antiinflammatory drugs.

Cellular uptake of T3 was examined using rat H4 hepatoma cells. Uptake of [125I]T3 (10(-11) M) from serum-free medium was measured as the cell-associated counts retained by washed cells (2 X 10(6) per well). Displaceable uptake was 84% of total uptake at 2 min (2.9% of total counts). T4, tetraiodothyroacetic acid, triiodothyroacetic acid, rT3, and D-T3 were 2-5% as effective as T3 in displacing uptake. Nonequilibrium kinetics indicated a half-maximal uptake at 680 nM T3 with approximately 7 million sites per cell. Displaceable uptake was time and temperature dependent and was 73% inhibited by 2 mM KCN and 52% by 10 mM bacitracin but not by 2 mM ouabain or 10 microM cytochalasin B. Phloretin, 100 microM, inhibited uptake by 66%. T3 uptake was directly related to the free T3 concentration over the range of albumin concentrations, 0-10 g/liter. The nonbile acid cholephil compounds, bromosulfophthalein, iopanoic acid, and indocyanine green (all 100 microM) inhibited T3 uptake to 62%, 17%, and 5% of control, respectively. Taurocholate, methylaminoisobutyric acid, and oleic acid were noninhibitory. The half-inhibitory concentrations of reactive nonsteroidal antiinflammatory drugs were: meclofenamic acid (25 microM), mefenamic acid (45 microM), fenclofenac (69 microM), flufenamic acid (100 microM), and diclofenac (230 microM). Aspirin, ibuprofen, oxyphenbutazone, and phenylbutazone (all 100 microM) were noninhibitory. Diphenylhydantoin inhibited uptake to 50% at 75 microM. These findings suggest that T3 uptake by cultured rat hepatocytes is by an energy-dependent, saturable, stereo-selective mechanism that is dependent on cell membrane proteins. This mechanism appears to be shared by a number of other ligands, including nonbile acid cholephils and several nonsteroidal antiinflammatory drugs of the anthranilic and phenylacetic acid classes, as well as diphenylhydantoin. The bile acid taurocholate, oleic acid, and a probe for type A amino acid uptake were inactive. The extent to which these effects may modify expression of thyroid hormone action remains to be established.

Aminoisobutyric Acids↗
PubMed1989

Drug competition for thyroxine binding to transthyretin (prealbumin): comparison with effects on thyroxine-binding globulin.

We examined the effect of 26 drugs on T4 binding to transthyretin (TTR; prealbumin) and T4-binding globulin (TBG) by determining their ability to inhibit [125I]T4 binding to TTR isolated from normal human plasma and to serum diluted 1:10,000, respectively. The hierarchies for drug inhibition of T4 binding differed greatly for these two proteins. Relative to T4, the drugs were much more potent inhibitors of [125I]T4 binding to TTR than to TBG. Compounds of the anthranilic acid class, such as flufenamic, meclofenamic, and mefenamic acids, interacted particularly strongly with TTR. Flufenamic acid was more potent than T4 itself in inhibiting [125I]T4 binding [175 +/- 17% (+/- SD); cf. T4; n = 3; P less than 0.001], while mefenamic acid, diflunisal, and meclofenamic acid were 20-26% as potent as T4 in their interaction with TTR. The reactivity of diclofenac, fenclofenac, indomethacin, sulindac, and the diuretic ethacrynic acid was 0.8-2.1% relative to that of T4. In contrast, furosemide, the drug most highly reactive with TBG, was only 0.11 +/- 0.03% (n = 7) as potent as T4, followed by meclofenamic acid greater than mefenamic acid greater than fenclofenac greater than flufenamic acid greater than diflunisal greater than milrinone. Aspirin and sodium salicylate were, respectively, 0.05% and 0.20% as active as unlabeled T4 as inhibitors of [125I]T4 binding to TTR, but these compounds had only 3-4 x 10(-6)% of the activity of T4 for TBG binding. Diphenylhydantoin had no detectable effect on T4 binding to TTR and was 2.9 x 10(-4)% as reactive as T4 with TBG. Amiodarone did not interact with either binding site. Drug interactions with TTR may be important when this protein becomes a major circulating T4-binding protein, as in patients with complete or partial TBG deficiency, or when serum T4 is markedly elevated. Such interactions may also be important where TTR is the dominant tissue T4-binding protein, as in the choroid plexus. In addition, the drug competitors described here may be useful as probes to further define the structural basis for specific ligand interactions with different classes of T4-binding sites.

Binding Sites↗
PubMed1989

Hyperthyroidism. Current drug therapy.

The choice of treatment for hyperthyroidism should be preceded by considering: (a) whether the diagnosis is correct; (b) the severity of the disorder; (c) the cause of the thyroid hormone excess; (d) factors such as patient age, size of goitre, associated diseases, previous treatment, and (e) patient preference. If hyperthyroidism appears to be severe, a judgement based on clinical rather than biochemical features, there is generally no safe alternative to the initial use of a drug from the thioamide thioureylene group (carbimazole, methimazole or propylthiouracil) to make the patient euthyroid as rapidly as possible. There are numerous different schedules for the use of these drugs, alone or in conjunction with surgery, radioactive iodine, or drugs such as beta-blocking agents, iodide or thyroxine. Patients can be made euthyroid with reasonable certainty, but an underlying abnormality often remains. The patient's understanding of the natural history of his or her condition is crucial in achieving adequate follow-up.

Humans↗
PubMed1989

The significance of subnormal, detectable TSH values: laboratory and clinical aspects.

In order to establish the significance of subnormal, detectable TSH values in the range 0.05-0.3 mU/L by sensitive immunoradiometric assay, we assessed 3150 consecutive tests of thyroid function in which TSH was measured on 1400. Sixty TSH values (4.3%) fell in this range and in 80% of these the result was confirmed on repeat assay. Conditions associated with subnormal detectable TSH values were treated hyperthyroidism (21), nonthyroidal illness (17), euthyroid multinodular goitre (10), T4 therapy for primary hypothyroidism (7), and pituitary disease (5). At follow-up 2-15 months later, a second sample showed that TSH remained in this range in only 9 of 41 patients (22%). These findings show a frequency of TSH values intermediate between normality and the suppressed values of hyperthyroidism sufficient to compromise the value of sensitive TSH measurement as the single initial test of thyroid function. While TSH values in the subnormal detectable range rule out hyperthyroidism, such results may merit follow-up in goitrous patients, in whom such a finding can precede overt hyperthyroidism.

Adult↗
PubMed1988

Furosemide, fenclofenac, diclofenac, mefenamic acid and meclofenamic acid inhibit specific T3 binding in isolated rat hepatic nuclei.

Previous studies with phenytoin (DPH) show that this inhibitor of thyroid hormone binding to plasma proteins also interacts with specific nuclear T3 binding sites. In order to further define the nuclear effects of drugs that inhibit plasma protein binding of thyroid hormones, we assessed furosemide and a number of non-steroidal antiinflammatory drugs using isolated rat liver nuclei. The effects were compared with those of DPH, ipodate and amiodarone. The T3 binding site in isolated nuclei (Ka 1.2 X 10(9)M-1) showed relative affinity triac approximately equal to T3 greater than T4. Drugs were studied over the concentration range 10(-3)-10(-7)M, approximating the known therapeutic total plasma concentrations, in competition with 125I-T3 0.1 nM, expressing inhibition as the percent decrement from maximum specific binding of 125I-T3 in drug vehicle (assay buffer or thanol 1-10%). Specific T3 binding was inhibited by furosemide to 78.8 +/- 3.5% at 2 mM, by fenclofenac to 37.6 +/- 2.8% at 1 mM, by meclofenamic acid to 70.2 +/- 2.4% at 0.1 mM, by mefenamic acid to 60.6 +/- 4.6% at 0.05 mM (each p less than 0.02) and by diclofenac to 87.4 +/- 5.6% at 0.2 mM (p less than 0.05). In comparison, DPH inhibited T3 binding to only 88.1 +/- 0.6% at 0.3 mM, as did calcium ipodate (68 +/- 3.5% at 1 mM, p less than 0.02). Amiodarone (0.3 mM), sodium salicylate (1 mM) and phenylbutazone (0.1 mM) were inactive. In order to achieve a level of nuclear receptor occupancy that approaches in vivo occupancy, the concentration 125I-T3 was increased over the range 0.1-0.5 nM.2+t

Amiodarone↗
PubMed1988

Amiodarone-induced hyperthyroidism: assessment of the predictive value of biochemical testing and response to combined therapy using propylthiouracil and potassium perchlorate.

In order to assess the value of thyroid function testing during amiodarone therapy, we reviewed all available tests in 128 patients treated with this drug. Nine patients (7.0%) developed biochemical hyperthyroidism with elevation of both free thyroxine index (FT4I) and free triiodothyronine index (FT3I) and marked suppression of serum thyroid stimulating hormone (TSH) after 1-46 months of therapy; six of these nine patients had clear clinical evidence of thyroid overactivity. Where serial tests were available before development of hyperthyroidism, this complication developed suddenly, despite previously stable normal indices of thyroid function, and could not be predicted by currently-available biochemical tests such as T4, T3, sensitive TSH, thyroglobulin or sex hormone binding globulin (SHBG) assays. Clinical features such as unexplained weight loss, proximal myopathy, exacerbation of arrhythmia, or heat intolerance appear to be the key to prompt diagnosis of this complication. Hyperthyroxinemia without T3 excess was found in 32.8% of patients without progression to true hyperthyroidism. Serum TSH remained detectable by sensitive assay in 17 out of 18 patients with amiodarone-induced euthyroid hyperthyroxinemia and was significantly higher than in patients with equivalent hyperthyroxinemia due to thyroxine therapy. Serial levels of SHBG were higher in patients with true hyperthyroidism than in those with euthyroid hyperthyroxinemia. The effect of combined treatment with propylthiouracil (800 mg/day) and potassium perchlorate (800 mg/day) was evaluated in five of the six clinically hyperthyroid patients. Biochemical euthyroidism was achieved after 7-19 weeks, a response slower than previously reported, indicating that this drug combination does not result uniformly in prompt resolution of amiodarone-induced hyperthyroidism.

Adolescent↗
PubMed1988

Drug and fatty acid effects on serum thyroid hormone binding.

We directly compared the competitor potency for serum T4 binding of 11 nonsteroidal antiinflammatory drugs; the diuretics furosemide, ethacrynic acid, and bumetanide; diphenylhydantoin; the cholecystographic contrast agents iopanoate and ipodate; and six long-chain nonesterified fatty acids (NEFA) using equilibrium dialysis. To avoid artefacts that occur in competitor studies with diluted serum or isolated binding proteins, we used undiluted normal serum, with drugs added at concentrations that achieved high therapeutic total and free serum levels at equilibrium. Drug addition was based on the measured free fraction of each drug in serum. The free T4 fraction in normal serum (Tris buffer, pH 7.4; 37 C) was between 1.40 X 10(-4) and 1.53 X 10(-4). Drug-induced increases in T4 free fraction were: fenclofenac, 90%; aspirin, 62%; meclofenamic acid, 39%; diflunisal, 37%; mefenamic acid, 31%; and furosemide, 31%. Significant increases of 7-15% occurred with diclofenac, flufenamic acid, phenylbutazone, and diphenylhydantoin. Indomethacin, ketoprofen, tolmetin, ethacrynic acid, bumetanide, iopanoate, and ipodate were inactive at the concentrations studied. Addition of 2.0 mmol/L oleic acid had a negligible effect, but 3.5 mmol/L oleic acid inhibited T3 and T4 binding significantly. Other long chain NEFA (addition of 1.5 mmol/L) gave increases in free T4 fraction as follows: arachidonic acid, 26%; linolenic acid, 23%; and linoleic acid, 11%. Stearic and palmitic acids were inactive. The effect of 5 mmol/L oleic acid in serum could be reproduced by addition of 0.5 mmol/L to serum diluted 1:10, indicating that protein binding of NEFA is the major determinant that limits their competitor potency. These findings provide a basis for anticipating which potential inhibitors may cause important changes in serum thyroid hormone binding. The time course of such effects will be influenced by the pharmacokinetics of the inhibitor itself as well as the equilibrium findings described here.

Anti-Inflammatory Agents, Non-Steroidal↗