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At least 127 records · Page 7Linked to original sources
PubMed1982

The effect of some iodine-containing radiocontrast agents on iodothyronine secretion from the perfused canine thyroid.

The effects of the iodine-containing radiocontrast agents ipodate, iopanoic acid, and iothalamate on the secretion of T4, T3, and rT3 were studied using perfused canine thyroid lobes. The experiments were performed as paired comparisons, with one thyroid lobe acting as a control. At 10(-5) M, the two agents used for cholecystography (ipodate and iopanoic acid) inhibited the TSH-stimulated secretion of T3 [ipodate, 69 +/- 8% of control (P less than 0.05); mean +/- SE; n =4] and rT2 [iopanoic acid 59 +/- 9% (P less than 0.01); iopanoic acid, 61 +/- 9% (P less than 0.05)], whereas T4 secretion was not significantly altered. Iothalamate (10(-3)M), an agent predominantly excreted through the kidneys, did not alter T4, T3, or rT3 secretion. This pattern is compatible with an inhibitory effect on intrathyroidal T4 deiodination to T3 and rT3 by ipodate and iopanoic acid, similar to the inhibition of T3 deiodinases in peripheral tissues by these compounds. At a concentration of 10(-3) M, ipodate induced a hitherto unrecognized pattern of thyroid hormone secretion: a very rapid, sustained and reversible inhibition of the secretion of all three iodothyronines. The mechanism behind this response remains to be elucidated.

Animals↗
PubMed1984

Does amiodarone affect heart rate by inhibiting the intracellular generation of triiodothyronine from thyroxine?

The hypothesis that the antiarrhythmic drug amiodarone slows down the heart rate by its inhibitory action on the intracellular conversion of thyroxine (T4) to 3,5,3' triiodothyronine (T3) was investigated. For this purpose we compared the effect of amiodarone with that of another potent inhibitor of the T4----T3 conversion, i.e. the radiographic contrast medium iopanoic acid, on the heart rate of unanaesthetized guinea-pigs. Both amiodarone and, to an even greater extent, iopanoic acid induced an increase in serum 3.5',3' triiodothyronine (reverse T3), indicating effective inhibition of T4----T3 conversion. Both amiodarone and iopanoic acid were accumulated in the liver and in the heart (measured as iodine). While amiodarone induced bradycardia, iopanoic acid did not change the heart rate. Supraphysiological amounts of exogenous T3 reverted the amiodarone induced bradycardia to near normal values. A comparable effect was observed with isoprenaline. The intracellular inhibition of the T4----T3 conversion is not the ultimate mode of the action of the amiodarone effect on heart rate. It is thought that amiodarone interacts with T3 at its receptor or somewhere later along the pathway from the T3-receptor interaction to the final effect of T3 on heart rate.

Amiodarone↗
PubMed1991

Rapid preoperative preparation in hyperthyroidism.

OBJECTIVE: We have evaluated an alternative method of preparation of hyperthyroid patients for surgery, using betamethasone, iopanoic acid and propranolol. DESIGN: Betamethasone (0.5 mg every 6 hours), iopanoic acid (500 mg every 6 hours) and propranolol (40 mg every 8 hours) were given orally for 5 days; thyroidectomy was performed on the 6th day. We analysed patient acceptability, clinical and hormonal effects, ease of surgery and final outcome. PATIENTS: Thirteen females and 1 male, aged 16-59 years, ten with diffuse goitre and four with nodular goitre were submitted to subtotal thyroidectomy because antithyroid drugs had failed to control thyrotoxicosis or because hyperthyroidism coexisted with other conditions (pregnancy, hypertensive disease). MEASUREMENTS: Daily clinical assessments were made together with T3, T4 and rT3 serum concentrations before and while on drug treatment, during the surgical procedure and post-operatively. RESULTS: Daily assessment showed progressive clinical improvement so that on day 5 the patients were considered clinically euthyroid. Serum levels of T3 (mean +/- SD) showed significant decrease (by 38.2 +/- 24.9%, P less than 0.01) as early as 24 hours after medication was started, reaching almost euthyroid levels on day 3; on the day of operation T3 had diminished by 64.5 +/- 16.6% (P less than 0.0001). Serum T4 concentration showed a slight but significant decrement only from day 4 on and never reached euthyroid levels. Serum rT3 values exhibited a brisk increment at 24 hours (+333 +/- 194%, P less than 0.0001) and remained elevated between 8 and 10 nmol/l until medication was stopped. Drug tolerance was considered as excellent since no serious side-effects were noted, even in pregnant patients. There were no anaesthetic incidents or postoperative complications and patients were discharged 48-72 hours after operation. The final outcome has been satisfactory and pregnant patients continued their pregnancies without incident, bearing normal children. CONCLUSIONS: Pharmacological combination of betamethasone, iopanoic acid and propranolol has proved to be safe and effective and is of low cost. Provided there is adequate supervision of the patients, it may be used in patients requiring urgent thyroidectomy or in those who for reasons of non-compliance need a short preoperative regime.

Adolescent↗
PubMed2003

Acute decrease in circulating T3 levels enhances, but does not normalise, the GH response to GHRP-6 plus GHRH in thyrotoxicosis.

In thyrotoxicosis there is an impaired GH response to GHRH, normal GH responsiveness to GHRP-6 and lack of synergistic GH response after simultaneous administration of both peptides. We have previously shown that the GHRH-induced GH release in these patients increases after an acute reduction of circulating T3 values with administration of iopanoic acid, a compound that inhibits peripheral conversion of T4 to T3. We have now studied the effect of a decrease in serum T3 levels on the GH response to GHRP-6 (1 microg/kg) plus GHRH (100 microg) in 9 hyperthyroid patients before and after 15 days of treatment with iopanoic acid (3 g every 3 days) and propylthiouracil (600 mg/day). Nine normal subjects were also studied. In all hyperthyroid patients iopanoic acid induced a rapid decrease and normalisation of serum T3 levels. In these subjects peak GH (microg/l; mean +/- SE) and AUC (microg/l x 120 min) values after GHRP-6 plus GHRH were significantly higher on day 15 compared to pretreatment values (peak, 18.3 +/- 3.0 vs 13.4 +/- 1.9; AUC, 1227.9 +/- 212.9 vs 968.5 +/- 160.4; p<0.05). Despite the significant enhancement of the GH responsiveness to GHRP-6 plus GHRH after treatment with iopanoic acid, this response remained significantly blunted when compared to controls both in terms of peak GH (18.3 +/- 3.0 vs 83.7 +/- 15.2; p<0.05) and AUC values (1227.9 +/- 212.9 vs 4956.5 +/- 889.3; p<0.05). In conclusion, our results show that an acute decrease of circulating T3 levels enhances, but does not normalise, the GH response to GHRP-6 plus GHRH in thyrotoxicosis. This could suggest that circulating T3 does not have a major role in the mechanisms involved in the synergistic effect of these peptides.

Adolescent↗
PubMedDate not supplied

Effect of iopanoate on the biliary and urinary excretion of iodipamide.

The effect of sodium iopanoate and iopanoic acid on the biliary excretion of iodipamide in dogs was studied. Enteric administration of sodium iopanoate within one hour of iodipamide infusion reduced biliary iodipamide excretion and increased urinary iodipamide output. The biliary and urinary excretion of iodipamide was not influenced by iopanoic acid administered 40 and then again 16 hrs before iodipamide. These results suggest that iodipamide cholangiography can be employed 16-18 hrs after a standard two-day iopanoic acid oral cholecystogram without decreasing the ability to visualize the biliary ductal system or increasing the urinary iodipamide excretion.

Animals↗
PubMedDate not supplied

Effect of choleretics on biliary and urinary excretion of cholecystographic agents.

Two choleretic agents, taurocholate and cinchophen, were studied in the dog to determine their effect on both the biliary and urinary excretion of two related cholecystographic agents, iopanoic acid and iophenoxic acid. Liver concentrations were determined on biopsies. Trace amounts of radioactively labeled compounds were used for measurements. The effect of the choleretic agent was specific for the cholecystographic compound. Taurocholate increased both biliary and urinary excretion of iopanoic acid and decreased its intrahepatic level, but had no effect on iophenoxic acid. Cinchophen had no effect on iopanoic acid but increased both biliary and urinary excretion of iophenoxic acid. When examined against a pre-existing high rate of bile flow, the active choleretic increased, rather than decreased, the biliary concentration of the cholecystographic compound. The increased excretion in both bile and urine cannot be attributed simply to the lessened concentration gradient from plasma to bile, as proposed by others. The data are consistent with a direct action of the choleretic agent on hepatic mechanisms, either to decrease intracellular binding or to alter the characteristics of transport.

Animals↗
PubMed1996

Maternal to fetal thyroxine transmission in the human term placenta is limited by inner ring deiodination.

Placental deiodination of T4 to rT3 has been proposed as the factor controlling materno-fetal transmission of T4. We investigated T4 transfer in the isolated perfused human placental lobule with and without addition of the deiodinase inhibitor, iopanoic acid. T4 (150 nmol/L) in protein-free medium was added to the maternal circuit. Without iopanoic acid, the appearance of T4 in the fetal circuit was very low, with fetal T4 levels reaching only 4.1 +/- 0.84 pmol/L at 6 h. Levels of rT3 rose progressively in both circuits, reaching 28.8 +/- 5.5 nmol/L in the maternal and 12.4 +/- 3.2 nmol/L in the fetal circuit by 6 h. No T3 could be measured in either circuit. Addition of 0.5 nmol/L iopanoic acid to maternal perfusate, however, resulted in significant reduction in the appearance of rT3 [maternal levels, 0.58 +/- 0.06 nmol/L (2% of control values); fetal levels, 0.33 +/- 0.03 nmol/L (2.7% of control values)] and a major (approximately 2700-fold) increase in T4 appearance in the fetal circuit, with fetal T4 levels reaching 10.1 +/- 3.4 nmol/L at 6 h. These results support the hypothesis that placental inner ring (type III) deiodination is a major factor controlling placental transmission of maternal T4.

Female↗
PubMed1978

The effect of fasting on gallbladder opacification during oral cholecystography: a controlled study in normal volunteers.

The effect of fasting on gallbladder opacification during oral cholecystography was studied in 10 normal volunteers using 2 oral cholecystographic agents, iopanoic acid and sodium tryopanoate. Radiographs made 15 hours after ingestion of the contrast agents revealed good opacification of the gallbladder in all subjects when iopanoic acid was administered with a meal and when sodium tyropanoate was administered in the fasting state; in only 2 subjects when iopanoic acid was given in the fasting state; in 3 when given in the fasting state with ox bile; and in 3 when sodium tyropanoate was given with a meal.

Administration, Oral↗
PubMed1984

Conversion of thyroxine to triiodothyronine in the anterior pituitary gland and the influence of this process on thyroid status.

There are two iodothyronine 5'-deiodinases in the rat anterior pituitary gland. The type II 5'-deiodinase is responsible for the observable T4 to T3 conversion in pituitary tissue, both in vivo and in vitro. This type II enzyme has kinetic characteristics which distinguish it from type I activity, and it is also insensitive to inhibition by propylthiouracil. Iopanoic acid is both a substrate for, and an inhibitor of, the pituitary type II 5'-deiodinase. Studies in the rat and in man using iopanoic acid as a probe indicate that conversion of T4 to T3 within the anterior pituitary is a necessary step in the expression of thyroid hormone effects on the thyrotrophic and somatotrophic cells after T4 administration. Amiodarone, which has effects on the human pituitary-thyroid axis similar to those of iopanoic acid, has little inhibitory activity on T4 5'-deiodination in rat pituitary homogenate. Phenytoin, which lowers the serum T4 after chronic administration without inducing an increase in thyrotropin, could theoretically act by enhancing intrapituitary T3 production. In actuality, phenytoin shows only inhibitory activity in vitro on type II 5'-deiodination in rat pituitary and brain homogenates and on type I activity in rat liver homogenates. Phenytoin treatment in vivo has no significant effect on T4 5'-deiodination in pituitary or liver homogenates either. Evidence is discussed regarding whether the increase in type II 5'-deiodinating activity in hypothyroidism, and the decrease in hyperthyroidism, are beneficial defense mechanisms; this is likely to be so in some parts of the body, but may ot be in the thyrotrophic cells of the anterior pituitary.

Animals↗
PubMed2000

Selenium influences growth via thyroid hormone status in broiler chickens.

As there is a possibility that Se influences the growth of animals via thyroid hormone metabolism, the following three experiments were undertaken in order to determine the effects of dietary Se on growth, skeletal muscle protein turnover and thyroid hormone status in broiler chickens. Broiler chickens were raised on a Se-deficient diet until 12 d of age and then used for the experiments. In Experiment 1, twenty-eight birds were randomly assigned to four groups and fed purified diets with the following amounts of Se supplementation: 0.0, 0.1, 0.3 and 0.5 mg Se/kg diet. Dietary Se supplementation significantly increased plasma 3,5,3'-triiodothyronine (T3) concentration and improved growth, while plasma thyroxine (T4) concentration was decreased. In Experiment 2, twenty-eight birds were assigned to four groups and fed either a Se-deficient diet or a Se-supplemented diet (0.3 mg Se/kg diet) with or without the supplementation of iopanoic acid, a specific inhibitor of 5'-deiodinase (5 mg/kg diet). The growth was promoted and feed efficiency was improved by dietary Se supplementation as was also observed in Experiment 1. However, this effect of Se was halted by iopanoic acid supplementation. Hepatic 5'-deiodinase activity was elevated by Se and inhibited by iopanoic acid. In Experiment 3, birds were fed on the following diets to show that Se influences growth of birds via thyroid hormone metabolism: Se-deficient diet, Se-supplemented diets (0.1 and 0.3 mg/kg) and T3 supplemented diets (0.1 and 0.3 mg/kg diet). Lower dietary T3 supplementation (0.1 mg/kg diet) resulted in growth promotion similar to Se supplementation, while higher level of T3 caused growth depression. Furthermore, it was observed that the rate of skeletal muscle protein breakdown tended to be increased by Se similarly to the effect of T3. In conclusion, it was shown in the present study that Se deficiency depresses growth of broilers by inhibiting hepatic 5'-deiodinase activity which causes lower plasma T3 concentration.

Analysis of Variance↗
PubMed1980

The effect of diet and fasting on gallbladder opacification during oral cholecystography in dogs as measured by computed tomography.

To determine the influence of diet and fasting on gallbladder opacification during oral cholecystography, 10 dogs were studied in a blind, random fashion, giving single or two consecutive doses of iopanoic acid, sodium tyropanoate, or sodium ipodate while the animals were fasting, on a normal diet, or on a low-fat diet. Gallbladder density was determined by CT to eliminate the bias created by subjective interpretation of radiographs. For maximum, first-dose gallbladder opacification during clinical cholecystography, iopanoic acid should be given with a meal and sodium ipodate while the patient is fasting; diet makes no difference with sodium tyropanoate. For maximum opacification with two consecutive doses, iopanoic acid may be given with a meal or during fasting, while sodium ipodate and sodium tyropanoate should be administered during fasting.

Administration, Oral↗
PubMed1980

A study of the relationship between thermogenesis and thyroid hormones.

To investigate the relationship between serum T3 levels and thermogenesis in euthyroid subjects, the conversion of T4 to T3 was partially blocked over a period of 3 weeks by weekly ingestion of 2 g iopanoic acid. Serum T3 decreased by 56 +/- 6 ng/100 ml without affecting the metabolic rate or total heat loss. Because an increase in serum T4 levels was observed (3.70 +/- 0.2 microgram/100 ml), the experiment was repeated in T4-substituted subjects. Serum T3 decreased even more in these subjects, (by 85 +/- 12 ng/100 ml), and the increase of serum T4 was also larger (4.6 +/- 0.7 microgram/100 ml). Again, the metabolic rate did not change. Experiments performed on hypothyroid patients and T3-substituted subjects demonstrated that iopanoic acid alone was without effect on the metabolic rate. Furthermore, the effect of a low energy, high protein diet (1672 kilojoules or 400 Cal) on the metabolic rate was confirmed. These results show that the decrease in magnitude of serum T3 seen with iopanoic acid is not sufficient by itself to reduce the metabolic rate.

Body Temperature Regulation↗
PubMed1999

Choledocholithiasis: diagnosis with oral-contrast-enhanced CT cholangiography.

OBJECTIVE: The objective of this investigation was to assess the performance of helical CT cholangiography after administration of an oral biliary contrast agent for the diagnosis of choledocholithiasis. SUBJECTS AND METHODS: Helical CT cholangiography was performed on 31 patients referred for endoscopic retrograde cholangiography of suspected choledocholithiasis. Iopanoic acid (6 g) was administered orally 8-12 hr before acquisition of helical CT cholangiograms. Three-dimensional and two-dimensional reformations were generated from a set of axial source images. Two radiologists independently interpreted the helical CT cholangiograms. Sensitivity and specificity were calculated using findings on retrograde cholangiography as the standard of reference. In addition, interobserver agreement was determined using kappa statistics. RESULTS: Our patients had no adverse reactions to iopanoic acid. The degree of biliary opacification was sufficient to perform three-dimensional and two-dimensional reconstructions in 29 patients (93.5%). Two patients were excluded from statistical analysis because cannulation of the common bile duct during retrograde cholangiography failed. Findings on endoscopic retrograde cholangiography in the remaining 29 patients were the following: choledocholithiasis (n = 14), common bile duct dilatation with no stones (n = 11), and normal bile ducts (n = 4). Sensitivity and specificity of oral-contrast-enhanced CT cholangiography for detection of choledocholithiasis were 92.9% (95% confidence interval [CI], 66.1-99.8%) and 100% (95% CI, 78.2-100%), respectively, for observer 1 and 85.7% (95% CI, 57.2-98.2%) and 100% (95% CI, 78.2-100%), respectively, for observer 2. Interobserver agreement was .92 (excellent). CONCLUSION: Helical CT cholangiography performed after oral administration of iopanoic acid appears promising for diagnosis of choledocholithiasis.

Administration, Oral↗
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↗
PubMed1992

Effects of thyroid hormones on mitochondrial oxygen consumption in brown adipose tissue and heart from cold-exposed hypothyroid rats.

The present work measured brown adipose tissue and heart mitochondrial oxygen consumption in hypothyroid rats treated with replacement doses of T3, T4 or T4 plus iopanoic acid and kept at 4 degrees C for 24 h. Heart oxygen consumption in normal, untreated hypothyroid and T4-treated hypothyroid rats was unaffected by cold exposure. In rats treated with T4 plus iopanoic acid, rates of oxygen consumption were normal in those maintained at 4 degrees C as well as in those kept at room temperature, despite serum T3 concentration being significantly decreased. The cold-exposed T3-treated hypothyroid rats showed a marked decrease in oxygen consumption (p less than 0.02) and alpha-glycerophosphate dehydrogenase activity, a T3-dependent enzyme. Mitochondrial oxygen consumption in brown fat from normal (p less than 0.01), T4 (p less than 0.02) and T4 plus iopanoic acid-treated (p less than 0.01) rats rose more than twofold in response to cold. In the T3-treated group, oxygen consumption at room temperature was higher (p less than 0.02) than in any other group at similar temperatures. However, the T3-treated group showed no changes in oxygen consumption in response to cold, perhaps because this group reached the maximal response at room temperature. The untreated and the T3-treated hypothyroid rats (both groups devoid of T4) did not survive at 4 degrees C unless T4 or several-fold replacement amounts of T3 were administered. The data demonstrate the crucial role of T4 in thermogenesis during cold exposure.

Adipose Tissue↗
PubMedDate not supplied

Gastrointestinal radiology. A study of iopanoate metabolism and toxicity in isolated cell cultures.

Radiologists are familiar with certain toxic manifestations of biliary and urinary contrast media (ie, acute tubular necrosis in dehydrated patients with diabetes or multiple myeloma), and with the specific effects of contrast media on other diagnostic tests (ie, I uptake, PBI, etc). These have been studied because of their clinical and diagnostic impact upon patient management. It has become apparent that many subtle, though perhaps predictable, drug interactions occur. Some of these are of obvious clinical and therapeutic significance and have been studied and described in detail. The authors have tried to establish the effects of clinically used drugs on the contrast medium iopanoic acid. The fact that both drugs thus far studied - aspirin and cholestyramine - have profound laboratory effects on iopanoic acid suggests that some systematic approach to the study of the clinical pharmacology of contrast agents is desirable. Others have also observed effects of contrast media on various clinical and laboratory parameters, but most observations are isolated empirical observations, and our basic understanding of the mechanisms involved are crude at best. How might this problem be approached? Although in vivo pharmacokinetic studies in unanesthetized animals allow identification of possible drug-drug interactions in the absence of multiple clinical variables and let us do crossover studies with each animal acting as its own control, such studies are difficult, expensive, and do little to establish the mechanism of the interaction. The authors are currently approaching this problem with a more basic technique. In conjunction with colleagues in gastroenterology and pharmacy, they are studying iopanoate metabolism and aspirin-iopanoate interaction in isolated hepatocyte monolayer cultures. The preliminary data from these experiments will be presented, and the significance of these results and the potential usefulness of this model will be discussed.

Animals↗
PubMed2005

Suppression of hypothalamic deiodinase type II activity blunts TRH mRNA decline during fasting.

Fasting is characterized by disrupted thyroid feedback, with suppressed levels of thyroid hormones and paraventricular thyrotropin releasing hormone (TRH). We found that third ventricle administration of the deiodinase inhibitor, iopanoic acid, dose-dependently reduced deiodinase type II (DII) activity selectively in the hypothalamus. This suppression of DII by iopanoic acid during fasting prevented elevated DII activity and blunted the decline in hypothalamic TRH mRNA levels. Because fasting-induced elevation in hypothalamic DII activity is paralleled by increased hypothalamic T3 concentration, our study suggests that T3 formation by DII in the hypothalamus is the cause of disrupted thyroid feedback during fasting.

Animals↗