triiodothyronine--reverse and 3--5--diiodothyronine

Topics: Chemical Phenomena; Chemistry; Diiodothyronines; Diiodotyrosine; Glucuronates; Humans; Hyperthyroidism; Iodine; Kinetics; Phenyl Ethers; Radioimmunoassay; Sulfates; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The present study was conducted to obtain information on the generation of diiodothyronines from triiodothyronines (3,3'-T2 from T3, and rT3, and 3',5'-T2 from rT3) as a result of the activity of the tissue monodeiodinase enzymes (MD) in the liver and kidney of pig fetuses and their mothers between 32 and 113 days of gestation. T3-5-MD activity in the fetal kidney during the gestational period was stable and higher than in the liver and in the maternal kidney. In contrast, T3-5-MD activity of the liver was 3-4 times lower in fetal than in maternal tissue in the first half of pregnancy, and in the second half of pregnancy 3,3'-T2 production from T3 in the maternal liver was equal to, or lower than, that in the fetal liver. The activity of MD deiodinating rT3 (3,3'-T2 and 3',5'-T2 generation) increased significantly in fetal liver and kidney in the last 2-3 weeks of pregnancy and was higher than in maternal tissues. In both tissues examined the inner ring deiodinating activity (IRD) was 5-10 times lower as compared to the outer ring (ORD).

Topics: Animals; Diiodothyronines; Embryonic and Fetal Development; Female; Gestational Age; Kidney; Liver; Pregnancy; Swine; Triiodothyronine; Triiodothyronine, Reverse

In the present study we report that 3,3',5-tri-iodothyronine (T3) as well as two iodothyronines (3,5-di-iodothyronine (3,5-T2) and 3,3'-di-iodothyronine (3,3'-T2)) significantly influence rat liver mitochondrial activity. Liver oxidative capacity (measured as cytochrome oxidase activity/g wet tissue) in hypothyroid compared with normal rats was significantly reduced (21%, P > 0.01) and the administration of T3 and both iodothyronines restored normal values. At the mitochondrial level, treatment with T3 stimulated respiratory activity (state 4 and state 3) and did not influence cytochrome oxidase activity. On the other hand, both the mitochondrial respiratory rate and specific cytochrome oxidase activity significantly increased in hypothyroid animals after treatment with 3,3'-T2 or 3,5-T2 (about 50 and 40% respectively). The actions of both iodothyronines were rapid and evident by 1 h after the injection. The hepatic mitochondrial protein content which decreased in hypothyroid rats (9.6 mg/g liver compared with 14.1 in normal controls, P < 0.05) was restored by T3 injection, while neither T2 was able to restore it. Our results suggest that T3 and both iodothyronines have different mechanisms of action. T3 acts on both mitochondrial mass and activity; the action on mitochondrial activity was not exerted at the cytochrome oxidase complex level. The action of the iodothyronines, on the other hand, is exerted directly on the cytochrome oxidase complex without any noticeable action on the mitochondrial mass.

Topics: Animals; Diiodothyronines; Electron Transport Complex IV; Hypothyroidism; Male; Mitochondria, Liver; Proteins; Rats; Rats, Wistar; Triiodothyronine, Reverse

A simple and rapid method for the estimation of cellular concentration of thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), and 3',5'-diiodothyronine (3',5'-T2) as well as their distribution between cytosol and membranes in human red blood cells (RBC) is presented. Concentrations of iodothyronines in RBC (RBC-T) were calculated by multiplying the total serum concentrations by the ratio of radioactivity in equal volumes of packed RBCs and serum, pre-incubated with 125I-labelled iodothyronines of high specific activity. Plasma and RBC were separated by centrifugation in capillary glass tubes. The separation of membranes and cystosol was performed by hypotone lysis and centrifugation. The median RBC-T of T4, T3, rT3, 3,3'-T2, and 3',5'-T2 from 17 euthyroid subjects were 360 pmol/l, 156 pmol/l, 2.77 pmol/l, 6.81 pmol/l, and 2.17 pmol/l, respectively. The cytosol/cytosol + membrane ration were 66%, 40%, 84%, 77%, and 97%, respectively. The differences in RBC-T were not similar to the differences in free serum concentrations. The ratio of RBC-T to free serum concentration differed considerably between T4 (16.6), T3 (24.4), and 3,3'-T2 (15.5) as compared to rT3 (5.8) and 3',5'-T2 (2.6). Data on three patients with thyroid diseases suggested that RBC-T values were increased in hyperthyroidism and decreased in hypothyroidism, whereas the cytosol/cytosol + membrane-ratio was unaltered.

Topics: Adult; Aged; Blood Proteins; Diiodothyronines; Erythrocytes; Female; Humans; Hypothyroidism; Male; Middle Aged; Receptors, Thyroid Hormone; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse; Ultrafiltration

We have studied the kinetics of 3 iodothyronines, 3,3'-diiodothyronine (T2), 3',5'-T2, and 3'-monoiodothyronine (T1), in groups of young adult male rats maintained under normal steady state physiological conditions. We have also performed a comparative analysis of these results, combined with corresponding kinetic indices of T4, T3, and rT3, to obtain a more comprehensive understanding of normal thyroid hormone production, distribution, and metabolism. Tracer doses of 125I-labeled 3,3'-T2, 3',5'-T2, and 3'-T1 were separately injected iv, and blood samples were collected 6-12 times for each iodothyronine in optimized sequential kinetic studies designed to maximize the precision of kinetic parameters. Labeled iodothyronines were separated quantitatively from their metabolites in each plasma sample by Sephadex G-25 column chromatography. Conventional kinetic analysis of the resulting data generated distribution volume, clearance, turnover, and mean residence time indices for each iodothyronine, and concomitant compartmental analysis of the same data provided additional results useful for integration and comparative analysis of the 6 iodothyronines. Kinetic parameters for all but T4 and T3 were similar, suggesting that similar mechanisms are responsible for the transport, metabolism, and distribution of nonhormonal iodothyronines. All but T4 and T3 (and, to a much lesser extent, 3'-T1) were almost completely and irreversibly metabolized, whereas 24-30% of the hormones (and 6% of 3'-T1) were excreted as such in feces only. Three-pool models fitted individual plasma kinetic data sets best in all cases (for all 6 iodothyronines), each with a plasma, a slowly exchanging (slow), and a rapidly exchanging (fast) pool, and kinetic parameters of interest were quantified for each iodothyronine (Ti). Quantitative analysis of an integrated 18-pool model for all 6 Tis revealed several other features of physiological interest. The fractional transport rate of T3 into the fast pool (liver, at least) is about an order of magnitude larger than that for all other Tis, supporting the hypothesis that transport of T3 into fast tissues (e.g. liver cells) is selectively amplified relative to that of the 5 other iodothyronines studied. Simultaneous and direct comparison of the 6 plasma kinetic data sets also supports this result. In addition, composite slow tissue pools, which probably exclude liver and kidney, contained the largest whole body fractions of all Tis (greater than 50%)

Topics: Animals; Diiodothyronines; Iodine Radioisotopes; Kinetics; Male; Rats; Rats, Inbred Strains; Thyronines; Thyroxine; Tissue Distribution; Triiodothyronine; Triiodothyronine, Reverse

The 24-h urinary excretion and renal clearance of thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), and 3',5'-diiodothyronine (3',5'-T2) were measured in 17 healthy subjects. The median urinary excretion was (pmol/24h) T4: 1242, T3: 828, rT3: 12.9, 3,3'-T2: 331, and 3',5'-T2: 5.8. The corresponding renal clearances were in median (ml/min) T4: 31, T3: 133, rT3: 15, 3,3'-T2: 683, and 3',5'-T2: 4.5. The clearances differed mutually (P less than 0.01) as well as from the creatinine clearance (P less than 0.01) which was in median 87 ml/min. Thus, all iodothyronines studied were subject to tubular transport mechanisms besides glomerular filtration. The 3 iodothyronines with 2 iodine atoms in the phenolic ring of the thyronine molecule, T4, rT3 and 3',5'-T2, were mainly tubularly reabsorbed, whereas those with only one iodine atom in the phenolic ring, T3 and 3,3'-T2, were mainly tubularly secreted. It might be hypothesized that the number of iodine atoms in the phenolic ring determines the direction of the tubular transport (presence of 2 iodine atoms is associated with tubular reabsorption, and of one iodine atom with secretion), whereas the rate of tubular transport decreases with decreasing number of iodine atoms in the tyrosylic ring.

Topics: Adult; Aged; Creatinine; Diiodothyronines; Female; Humans; Kidney; Male; Middle Aged; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

Cholecystographic radiocontrast agents interfere with thyroid hormones in several ways. In the present study 1 mM ipodate induced a rapid sustained and reversible inhibition of the secretion of T4, T3, rT3, 3,3'-diiodothyronine, and 3',5'-diiodothyronine from perfused dog thyroid lobes. This effect was not reproduced by infusion of 3 mM iodide and not affected by 2 mM methimazol or 2 mM perchlorate. One millimolar of ipodate inhibited secretion of T4 to 23.7 +/- 2.8% of control (+/- SE, n = 6), 0.3 mM ipodate to 59.6 +/- 3.01 (n = 4), and 0.1 mM ipodate to 80.4 +/- 5.7% of control (n = 4). In search of the site of action in the thyroid of this inhibitory compound it was found that 1 mM ipodate inhibited TSH-induced increase in thyroidal cAMP, cAMP-induced generation of intracellular colloid droplets, and liberation of T4 and T3 from thyroglobulin by acid proteases and peptidases. These processes are those thought to be inhibited during iodide inhibition of thyroid secretion, via gradual formation of an unknown iodine-containing organic intermediate. It is suggested that the inhibition of thyroid secretion observed in the present study is due to structural similarities between ipodate and this putative iodine-containing mediator of the iodide-induced inhibition of thyroid secretion.

Topics: Animals; Cyclic AMP; Diiodothyronines; Dogs; Iodine; Ipodate; Perfusion; Thyroglobulin; Thyroid Gland; Thyronines; Thyrotropin; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

1H NMR data of a series of thyroid hormone analogues, e.g., thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), 3,5-diiodothyronine (3,5-T2), 3',5'-diiodothyronine (3',5'-T2), 3-monoidothyronine (3-T1), 3'-monoiodothyronine (3'-T1), and thyronine (TO) in dimethylsulfoxide (DMSO) have been obtained on a 300 MHz spectrometer. The chemical shift and coupling constant are determined and tabulated for each aromatic proton. The inner tyrosyl ring protons in T4, T3, and 3,5-T2 have downfield chemical shifts with respect to those of the outer phenolic ring protons. Four-bond cross-ring coupling has been observed in all the monoiodinated rings. However, this long-range coupling does not exist in T4, diiodinated on both rings, and T0, containing no iodines on the rings. There is no evidence that at 30 degrees C these iodothyronines have any motional constraint in DMSO solution. In addition to identification of the hormones, the potential use of some characteristic peaks as probes in binding studies is discussed.

Topics: Diiodothyronines; Magnetic Resonance Spectroscopy; Thyroid Hormones; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

The extrathyroidal metabolism of T4, T3, rT3, and 3',5'-diiodothyronine (3',5'-T2) was studied before and after treatment with 350 mg phenytoin (DPH) daily for 14 days in six hypothyroid patients receiving constant L-T4 replacement. The total and free serum concentrations of the four iodothyronines were reduced by approximately 30% during DPH treatment, whereas the free fractions in serum were unaltered. Concomitantly, serum TSH increased 137% (P less than 0.02). The production rate (PR) of T4 decreased 16% (P less than 0.005), indicating decreased intestinal absorption (bioavailability) of oral L-T4 during DPH treatment. The fractional rate of 5'-deiodination of T4 to T3 increased from 27% to 31% (P less than 0.05), whereas the rate of 5-deiodination of T4 to rT3 decreased from 45% to 25% (P less than 0.05). The urinary excretion of free and conjugated T4 was 2.3% of the T4 PR and was unaffected by DPH. Thus, the amount of T4 metabolized through nondeiodinative pathways apart from urinary excretion increased from 25% to 44% (P less than 0.05). The apparent distribution volume (Vd) of T4 increased (P less than 0.05), whereas the pool size was unchanged. The PR of T3 did not change during DPH treatment, nor did the mean transit time or the cellular clearance. The rT3 PR was reduced by 54% (P less than 0.02) during DPH treatment. Concomitantly, the transit time increased 10-fold (P less than 0.05), whereas Vd and pool size increased 5-fold (P less than 0.01 and P less than 0.05, respectively). The turnover of 3',5'-T2, in contrast to that of the other iodothyronines, did not change significantly during DPH treatment. T3 formation from T4 was measured in liver microsomal fractions from rats treated for 8 days with DPH and was almost identical to that in untreated animals. The data demonstrate that DPH in therapeutic concentrations did not affect serum protein binding of the iodothyronines. DPH reduced the intestinal absorption of T4 and increased the nondeiodinative metabolism of T4. The resulting decrease in total and free serum T4 and T3 was associated with an increase in serum TSH, demonstrating reduced negative feedback on the pituitary. Our data do not support the assumption that DPH induces increased hepatic deiodinating enzyme activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: Aged; Animals; Biotransformation; Diiodothyronines; Female; Humans; Hypothyroidism; In Vitro Techniques; Kinetics; Male; Microsomes, Liver; Middle Aged; Phenytoin; Rats; Rats, Inbred Strains; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse

A simple and accurate method for estimation of the free fractions (FFT) of T4, T3, rT3, 3,3'-diiodothyronine (3,3'-T2) and 3',5'-diiodothyronine (3',5'-T2) in serum is presented. The method is based on ultrafiltration of serum pre-incubated with tracers of high specific activity, followed by purification of the ultrafiltrate on small Sephadex columns. The addition of tracer only dilutes serum negligible (about 5%) and the ultrafiltration procedure only removes about 7% of the volume of serum, thus probably not disturbing the equilibrium between the free and protein bound fraction of iodothyronine. Progressive reduction of tracer to less than 10% of the amount usually used did not reduce the FFT of any of the iodothyronines. In contrast, addition of T4 to serum led to an increase of all FFTs except that of 3',5'-T2. These data suggest that FFT of T4, T3, rT3 and 3,3'-T2 primarily is determined by the amount of T4 present in serum and that significant amounts of these iodothyronines are bound to TBG, whereas 3',5'-T2 possibly primarily is bound to albumin. The median FFT of T4, T3, rT3, 3,3'-T2 and 3',5'-T2 in serum from euthyroid subjects (n = 38) was: 0.030, 0.29, 0.14, 1.10 and 1.07%, respectively. The corresponding median free concentrations in pmol/l were: 30, 4.79, 0.59, 0.44 and 0.77, respectively. Pregnant women in 3rd trimester had normal levels of free T4, free T3 and free rT3, whereas the median free 3,3'-T2 was reduced in contrast to elevated median free 3',5'-T2.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adult; Aged; Diiodothyronines; Female; Humans; Hyperthyroidism; Kidney Failure, Chronic; Liver Cirrhosis, Alcoholic; Male; Middle Aged; Pregnancy; Thyronines; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse; Ultrafiltration

These studies were performed to evaluate the quantitative role of monodeiodination in the peripheral metabolism of T3 and rT3 in man. As a prerequisite step, the serum concentrations of two diiodothyronines (T2s), 3,5-T2 and 3',5'-T2, were established by specific RIAs. In 20 normal subjects, mean (+/- SEM) serum concentrations of 3,5-T2 and 3',5'-T2 were 0.40 +/- 0.18 and 2.07 +/- 0.13 ng/dl, respectively. The mean concentrations of both T2s were significantly increased in hyperthyroidism. In primary hypothyroidism, the mean 3,5-T2 concentration was not significantly different from normal, but 3',5'-T2 concentrations were undetectable in the majority of subjects. In the first experiments, the MCRs of rT3 and all three T2s were derived by the constant infusion method. Seven normal subjects were infused simultaneously with the three 125I-labeled T2s for 12 h, and in four of the subjects, [131I]rT3 was also administered. The MCRs (liters/day . 70 kg; mean +/- SEM) were: rT3, 130 +/- 17; 3,5-T2, 168 +/- 15; 3,3'-T2, 621 +/- 84; and 3',5'-T2, 305 +/- 45. The daily production rates (PR; micrograms per day/70 kg; mean +/- SEM) were: rT3, 29.1 +/- 1.0; 3,5-T2, 0.6 +/- 0.1; 3,3'-T2, 20.8 +/- 4.1; and 3',5'-T2, 5.7 +/- 2.1. In the four subjects who received [131I]rT3, the serum T2 concentrations and PRs were also derived by turnover rate techniques. At equilibrium, 2.0 +/- 0.7% and 6.0 +/- 1.6% of [131I] rT3 were found as [131I]3,3'-T2 and [131I]3',5'-T2, respectively. The serum T2 concentrations were derived by the product of these percentages and the serum rT3 concentrations and compared with those obtained by T2 RIA. The serum 3',5'-T2 concentration was 1.3 +/- 0.4 ng/dl (tracer), and its PR was 3.4 +/- 1.1 micrograms/day (tracer); these values were closely correlated with those obtained by RIA. Serum 3,3'-T2 concentrations were 0.4 +/- 0.2 ng/dl (tracer) and 2.7 +/- 0.4 ng/dl (RIA), and the PRs were 3.2 +/- 1.6 micrograms/day (tracer) and 20.3 +/- 5.7 micrograms/day (RIA), indicating that rT3 5'-deiodination contributes only a small proportion of serum 3,3'-T2 and its PR. An analysis of the rT3 PR and the 3,3'-T2 and 3',5'-T2 PRs derived from the turnover of rT3 revealed that 28% of the rT3 produced was degraded by monodeiodination. Of this total, 49% of the deiodination occurred at the 5' position and 51% occurred at the 5 position.(ABSTRACT TRUNCATED AT 400 WORDS)

Topics: Chemical Precipitation; Chromatography, Ion Exchange; Chromatography, Paper; Diiodothyronines; Humans; Hypothyroidism; Immunochemistry; Iodine; Metabolic Clearance Rate; Radioimmunoassay; Triiodothyronine; Triiodothyronine, Reverse

A new radioimmunoassay for 3',5'-diiodothyronine (3',5'-T2) is described. The detection limit was 1-2 pmol/l with a sample size of 200 microliters. Cross-reaction with T4, T3, and rT3 was 0.005, 0.003, and 1.3% respectively. The intra- and interassay coefficients of variation were 5.1% and 9.2%. Dilution curves of effluent from perfused thyroid lobes of thyroid hydrolysate were parallel to the standard curve. By addition of 3',5'-T2 or rT3 standards to thyroid effluent sampling tubes or to thyroid homogenate before hydrolysis it was ascertained that no artifactual loss of 3',5'-T2 or generation of 3',5'-T2 from rT3 was taking place during collection and storage of thyroid effluent or during hydrolysis of thyroid homogenate. 3',5'-T2 was measured in effluent from perfused thyroids and in hydrolysate of the thyroids in six mongrel dogs. Only minute amounts of 3',5'-T2 was found: 1.66 +/- 0.41 pmol/mg thyroid wet weight (mean +/- SD) in hydrolysate, around 20 pmol/l in thyroid effluent during control perfusion and around 170 pmol/l during prolonged infusion of 100 micro U/ml bovine TSH. By measuring the apparent 3',5'-T2 concentration in perfusion medium with added T4 and rT3 standard corresponding to the amounts present in thyroid effluent samples, and dilutions of thyroid hydrolysates it was excluded that T4 and rT3 interference could account for more than maximally 20% of the measured 3',5'-T2. Thus 3',5'-T2 is present in the thyroid and secreted from the thyroid, but only in very small amounts.

Topics: Animals; Diiodothyronines; Dogs; In Vitro Techniques; Kinetics; Radioimmunoassay; Thyroid Gland; Thyronines; Thyrotropin; Thyroxine; Triiodothyronine, Reverse