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I J Chopra

Publications and source records attributed to I J Chopra.

At least 19 recordsLinked to original sources
PubMed1992

Analysis of nuclear 3,3',5-triiodothyronine receptor in the brown adipose tissue (BAT) of the postnatal lamb.

Postnatal thermogenesis in sheep is associated with increased sympathoadrenal activities, a T3 surge and an enhanced brown adipose tissue (BAT) type II 5'-monodeiodinating (5'-MDI) activity. The latter peaks 3-4 days after birth and is known to be important in generating intracellular T3 for nuclear receptor binding. In order to further investigate the mechanism(s) responsible for neonatal thermogenesis, thyroid hormone nuclear receptor (T3NR) binding characteristics were quantified in lamb BAT from newborn (NB) to 30d of postnatal age. Maximal binding capacities (MBC, mean +/- SEM fmoles T3/mg DNA) in BAT showed a decrease as studied by ANOVA during the first 11 days (NB to 1d, 148 +/- 24 [N = 5, p < 0.01, cf. 3-5d group]; 3-5 d, 61 +/- 5.5 [N = 5]; 10-11d, 72 +/- 9.1 [N = 4]). Afterwards, MBC increased at 30d (196 +/- 32, N = 4, p less than 0.01, cf. 3-5d group). BAT T3NR binding affinities (10(9) M-1) were comparable in all age groups studied (NB-1d, 2.8 +/- 0.3; 3-5d, 3.4 +/- 0.3; 10-11d, 4.0 +/- 1.1; 30d, 2.4 +/- 0.4). The data suggest that the postnatal surge in T3 and type II 5'-MDI is accompanied with a concurrent decrease in MBC of BAT T3NR. The latter may represent a down-regulation of T3NR presumably in an attempt to regulate the overall effect of thyroid hormone in neonatal thermogenesis.

Adipose Tissue, Brown↗
PubMed1992

Metabolism of 3,5,3'-triiodothyronine sulfate by tissues of the fetal rat: a consideration of the role of desulfation of 3,5,3'-triiodothyronine sulfate as a source of T3.

We have recently demonstrated that serum concentration of 3,5,3'-triiodothyronine sulfate (T3S) is markedly elevated in the human newborn at a time when serum 3,5,3'-triiodothyronine (T3) is very low. The present study explores the ability of maternal (19-21 d pregnant) and near-term fetal Sprague-Dawley rat tissues to 1) monodeiodinate T3S and T3 in both the outer and the inner ring and 2) desulfate T3S to T3. Maternal liver microsomes metabolized T3S exceedingly efficiently (compare fetus p less than 0.05). Eighty percent or more of T3S was consumed during its incubation with 360 micrograms/mL microsomes for 2 h. The majority of the consumption of T3S by adult liver microsomes occurred by its 5'-monodeiodination to I-; little inner-ring monodeiodination to 3,3'-diiodothyronine was demonstrable. In fetal liver microsomes, however, over 75% of the substrate T3S remained unchanged after a 2-h incubation. T3 was metabolized similarly moderately by fetal and maternal liver microsomes. Brain microsomes metabolized T3S poorly in both the mother and the fetus. Over 90% of substrate T3S remained unchanged after a 2-h incubation in each case. Interestingly, brain microsomes metabolized T3 more rapidly than T3S (p less than 0.05). In the fetus, desulfation of T3S to T3 was clearly evident only in microsomes from the liver and the brain; in the adult, it was plentiful in many tissues. Fetal liver and brain tissues metabolize T3S poorly, and both actively desulfate T3S to T3. These data and those indicating high serum T3S in the fetus suggest that T3S is a local source of T3 in critical tissues in the fetus and possibly in adults with the low T3 syndrome.

Animals↗
PubMed1992

A study of the characteristics of the rat placental iodothyronine 5-monodeiodinase: evidence that it is distinct from the rat hepatic iodothyronine 5'-monodeiodinase.

Recent studies have demonstrated that rat liver type I iodothyronine 5'-monodeiodinase (5'-MD) characteristically contains selenocysteine. The present study was undertaken to characterize rat placental type III iodothyronine 5-MD and to compare it with 5'-MD. Solubilized rat placental microsomes were delipidated by carboxymethyl cellulose-Sephadex chromatography. Phospholipids and proteins were recovered in two distinct peaks, which did not show 5-MD activity. 5-MD activity was recovered fully, however, by combining the two components (phospholipids and protein) and partially after the addition of exogenous phospholipids to protein. Tissue selenoproteins were labeled by injection of radioactive selenium (75Se; 50 microCi, iv; on days 5, 10, and 15 of gestation) to pregnant rats. Subcellular fractions of maternal and fetal tissues were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by autoradiography. No specific seleno-labeled proteins were evident in the microsomes of placenta or maternal or fetal brain. A 27- to 29-kilodalton (kDa) band previously suggested to be 5'-MD was observed, however, in maternal liver and kidney microsomes. Aurothioglucose inhibited rat placental 5-MD, but the dose required for 50% inhibition was over 50-fold greater than that for Se-containing hepatic 5'-MD (430 vs. 8 nM). The mechanism of the inhibition was noncompetitive for 5-MD, whereas it was competitive for 5'-MD. A synthetic peptide of 16 amino acids corresponding to the carboxy-terminal portion of 5'-MD was synthesized, and rabbits were immunized with the peptide-BSA conjugate. Western blots studies using the rabbit antiserum showed one specific 29-kDa band in rat liver microsomes. However, no specific bands were observed in 5-MD-rich placental or fetal brain microsomes. Bromoacetyl T3 (BrAcT3) was a potent inhibitor of rat placental 5-MD. Affinity labeling of solubilized rat placental microsomes with [125I]BrAcT3 showed a predominant band of 31 kDa, distinct from the 27- to 29-kDa band found in liver and kidney. The labeling of the 31-kDa band was enhanced by 10 mM dithiothreitol, inhibited 60% by 150 microM T3, and prevented by 40 microM aurothioglucose. A dominant affinity-labeled 31-kDa band was also observed in fetal brain microsomes. Some tissues without 5-MD activity (testes and spleen) also showed weak binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

A study of the characteristics of hepatic iodothyronine 5'-monodeiodinase in various vertebrate species.

Rat type I iodothyronine 5'-monodeiodinase (5'-MD) has recently been shown to be a selenium-containing enzyme. In the present study we compared the characteristics of the 5'-MD from liver microsomes of rat, mouse, guinea pig, man, beef, pig, sheep, and chicken. Aurothioglucose (ATG), a known potent inhibitor of selenium-containing enzymes, was a consistent, very potent inhibitor of 5'-MD activity in all species studied, with a 50% inhibitory dose in the narrow range of 5.8-12 nM. ATG was also a potent and selective inhibitor of [125I]bromoacetyl T3 affinity labeling of 5'-MD. Thus, in the species studied, only one affinity-labeled band, which was selectively displaced by gold, was identified. The mol wt of the affinity-labeled proteins in various liver microsomal preparations ranged between 28-36 kilodaltons (kDa), and the ATG concentrations necessary for the inhibition of affinity labeling of microsomes with [125I]bromoacetyl T3 were comparable to those required for inhibition of the enzyme activity in all species except the pig. The pig liver microsomes demonstrated a dominant affinity-labeled 36-kDa band, but much higher ATG concentrations (micromolar) were required for inhibition of affinity labeling. In view of the potent inhibition of pig liver 5'-MD activity by ATG, it appears unlikely that this band in the pig corresponds only to the substrate-binding site of 5'-MD, but this issue requires further study. A synthetic peptide of 16 amino acids corresponding to the carboxy-terminal portion of rat 5'-MD was synthesized, and rabbits were immunized with the peptide-BSA conjugate. Western blot studies using the rabbit antiserum showed one specific 29-kDa band in rat liver and kidney microsomes and thyroid homogenate. No specific bands were observed in other adult rat tissues studied or in fetal rat liver. No specific bands were observed when Western blot studies with antibody against the carboxy-terminal portion of rat 5'-MD were performed in liver microsomes from species other than the rat. In conclusion, our studies indicate that selenium is a likely component of type I 5'-MD in all species studied. However, substantial structural differences exist between the rat type I 5'-MD and that in various other species.

Affinity Labels↗
PubMed1992

A study of metabolism of deaminated and sulfoconjugated iodothyronines by rat placental iodothyronine 5-monodeiodinase.

The interaction of the rat placental type III iodothyronine 5-monodeiodinase (5-MD) with acetic acid (AA), propionic acid (PA), and sulfoconjugate (SA) derivatives of thyroid hormones has been investigated in comparison with hepatic iodothyronine type I MD. PA and AA derivatives of both T3 and T4 were potent inhibitors of 5-monodeiodination of [125I]T3 by rat placental microsomes. 3,5,3'-Triiodothyroacetic acid (T3AA) and 3,5,3'-triiodothyropropionic acid (T3PA) were comparable to T3 in their ability to inhibit 5-monodeiodination of [125I]T3, whereas T4AA and T4PA were more potent than T4. 3,5,3'-triiodothyrosulfonic acid (T3SA), T4SA, and rT3SA caused little or no inhibition of placental 5-MD activity. Among various analogs of T3 or T4, the order of relative potency of inhibition of hepatic 5'-MD was PA > AA > SA > parent iodothyronine. The metabolism of T3 and its derivatives by rat placental microsomes was studied by determining the rates of disappearance of the various substrates and the production of the metabolites generated by inner ring monodeiodination of the substrate. T3AA and T3PA were metabolized at a rate comparable to that of T3. Under the same conditions, essentially 100% of T3SA remained intact. Kinetic studies of placental inner ring monodeiodination of T3, T3AA, and T3PA demonstrated comparable values for Km (1.3, 1.8, and 2.3 nM, respectively) and maximum velocity (44, 57, and 74 fmol/micrograms.h, respectively). All derivatives of T3 studied were deiodinated by hepatic type I MD more avidly than the parent iodothyronine. Our data suggest that 1) deamination does not appreciably influence, while sulfoconjugation markedly inhibits type III 5-monodeiodination of T3; and 2) deamination may be even more conducive to degradation of thyroid hormone than sulfoconjugation.

Animals↗
PubMed1992

A radioimmunoassay of rat type I iodothyronine 5'-monodeiodinase.

A highly sensitive, specific, and reproducible RIA has been developed to measure rat type I iodothyronine 5'-monodeiodinase (5'-MD). A 16-amino acid peptide (LAP-744) corresponding to a portion of the carboxy-terminal region of the rat liver 5'-MD, as predicted from its cDNA, was synthesized, and rabbits were immunized with the peptide-BSA conjugate. In a final dilution of 1:15,000, our anti-5'-MD antibody bound about 30-35% of a tracer amount of [125I]LAP-744. The detection threshold of the RIA approximated 0.08 pmol LAP-744 or an equivalent amount of 0.08 pmol 5'-MD. Rat liver and kidney microsomes produced dose-response curves that were essentially parallel to that of LAP-744. No inhibition of binding of [125I]LAP-744 to antibody was produced by 0.3 mg or less rat microsomal proteins from testes, heart, brain, muscle, spleen, intestine, lung, placenta, or fetal liver. Recovery of nonradioactive LAP-744 added to spleen microsomes averaged 103%. The coefficient of variation averaged 4% within an assay and 11% between assays. In 16 normal rats studied, the mean (+/- SD) 5'-MD content was 2.4 +/- 0.22 pmol/mg protein in liver microsomes and 2.5 +/- 0.27 pmol/mg protein in kidney microsomes. Fasting of the rat for 2-4 days was associated with a significant reduction in both the activity and the content of the 5'-MD in liver and kidney. Hypothyroidism was also associated with a significant decrease in the activity and content of 5'-MD in both tissues. Significant opposite changes were observed in these parameters in hyperthyroidism. Treatment of the rat with sodium ipodate for 3 days was associated with a significant decrease in both the activity and the content of 5'-MD in liver and kidney. A similar treatment of the rat with propylthiouracil induced a clear reduction in the activity of 5'-MD in liver and kidney, but the content of the enzyme was significantly increased in both tissues. Rats treated with aurothioglucose for 3 days exhibited a significant decrease in 5'-MD activity in liver and kidney microsomes, whereas the tissue content of 5'-MD was not affected. A similar treatment of the rat with methimazole had no significant effect on either the activity or the content of 5'-MD.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1992

Evidence that the human placental 5-monodeiodinase is a phospholipid-requiring enzyme.

Gel filtration (GFI) of the solubilized human placental microsomes (SHPMP) performed in an Ultrogel AcA-34 column in the presence of 1 mM 3-(3-cholamidopropyl)dimethylammonio-1-propane sulfonate (CHAPS) plus 10 mM n-octyl-beta-D-glucopyranoside (beta-OG) demonstrated two main protein peaks. The 5-Monodeiodinase (5-MD) activity measured by the conversion of [125I]T3 to [125I]3,3'-diiodothyronine in a 2- to 18-h incubation at 37 C in the presence of 10 mM dithiothreitol was detected only in the first peak, and the specific activity was increased about 9 times over that of the starting SHPM. The fractions containing most of the 5-MD activity were filtered through a second Ultrogel AcA34 column (GFII) in the presence of 2 mM CHAPS plus 20 mM beta-OG. In these conditions, 5-MD activity was detected in low amounts only in the second peak. Cation exchange chromatography on carboxymethylcellulose-Sephadex with a starting buffer of pH 5 containing 2 mM CHAPS plus 20 mM beta-OG, followed by a pH 8 buffer, showed a very small OD peak at the void volume (P) and a second peak with about 95% of the protein (E). However, no 5-MD activity was detectable in either peak, while a nearly complete restoration of the enzyme was achieved when P and E were mixed. 5-MD was also completely restored by combination of P with the first inactive peak of GFII. When P was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, no distinct protein bands were observed. After ethanol-ether extraction and digestion with H2SO4 and H2O2, inorganic phosphate was detectable only in P, suggesting the presence of phospholipids. We next studied the effect of phosphatidyl serine (PS), phosphatidyl choline (PC), or phosphatidyl ethanolamine (PE) on 5-MD activity of E (5 micrograms protein/mL). The 5-MD activity was recovered in a dose-response manner with all phospholipids studied, but PS was the most effective agent for reconstitution. At 1 microgram/mL, 5-MD activity, expressed as a percentage of the total P plus E activity, was 101% for PS, 35% for PC, and 20% for PE. The addition of rat liver or kidney microsomes (80 micrograms/mL) to E (5 micrograms/mL) provided recoveries of 79% and 48%, respectively, of the total P plus E activity. The following conclusions were reached. 1) Phospholipids are essential for the 5-MD activity of SHPMP. 2) CHAPS and beta-OG may extract phospholipids from the membranes without denaturation of the 5-MD.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholic Acids↗
PubMed1992

A radioimmunoassay for measurement of 3,5,3'-triiodothyronine sulfate: studies in thyroidal and nonthyroidal diseases, pregnancy, and neonatal life.

A highly sensitive, specific, and reproducible RIA has been developed to measure T3 sulfate (T3S). Only T4 sulfate cross-reacted significantly (approximately 3%) in the RIA; rT3 sulfate, T4, T3, rT3, and diiodothyronine cross-reacted less than 0.01%. T3S was bound by thyronine-binding globulin and albumin in serum. The free fraction of T3S in four normal sera averaged 0.25% compared to a value of 0.35% for T3. Therefore, T3S was measured in ethanol extracts of serum. Recovery of the nonradioactive T3S added to serum averaged 92%. The dose-response curves of inhibition of binding of [125I]T3S to anti-T3S antibody by serial dilutions of serum extracts were essentially parallel to the standard curve. The detection threshold of the RIA was 20 pmol/L (1.5 ng/dL). The coefficient of variation averaged 7.8% within an assay and 11% between assays. The serum concentration of T3S was (mean +/- SE) 76 +/- 7.2 pmol/L in normal subjects, 268 +/- 29 in hyperthyroid patients with Graves' disease, 92 +/- 28 in hypothyroid patients, 201 +/- 32 in patients with systemic nonthyroidal illnesses, 40 +/- 6.2 in pregnant women (15-31 weeks gestation), and 429 +/- 39 in cord sera of newborns; the values in hyperthyroidism, nonthyroidal illnesses, and newborns were significantly different from normal (P less than 0.01). The mean concentration of T3S in amniotic fluid samples at 15-31 weeks gestation (90 +/- 1.3 pmol/L) was significantly higher than the corresponding value in maternal serum (P less than 0.05) and significantly lower than the corresponding value in newborn cord blood serum (P less than 0.001). Oral administration of sodium ipodate (Oragrafin; 3 g) to two hyperthyroid patients was associated with a 76-190% increase in serum T3S at 8 h, followed by a gradual decrease to a nadir that was 25-60% of the baseline value 2-3 days after ipodate ingestion. We conclude that 1) T3S is a normal component of human serum, and its levels change substantially in several physiological and pathological conditions; 2) sulfation pathway plays an important role in the metabolism of iodothyronines in man; and 3) high serum T3S levels in newborns and low normal levels in pregnancy despite elevated thyronine-binding globulin levels may signify markedly different metabolism of T3S in the mother and fetus.

Adolescent↗
PubMed1992

Biochemical studies of the relationship between iodothyronine 5'-monodeiodinase and protein disulphide isomerase in rat liver.

The relationship between type I iodothyronine 5'-monodeiodinase (5'-MD) and protein disulphide isomerase (PDI) was investigated by using a synthetic 18-amino acid peptide (LAP475c), which corresponds to the sequence of amino acids at position 373-390 of PDI including its active site, and anti-LAP475c antibody. Western blot analysis revealed that our anti-LAP475c antibody was highly specific for 57K protein in solubilized rat liver microsomal protein (SRLMP) that corresponded to PDI. Anti-LAP475c IgG (1:100 dilution) precipitated 46% of 5'-MD. These data suggest that PDI may play a regulatory role in the 5'-monodeiodination reaction.

Amino Acid Sequence↗
PubMed1991

Further studies on the long-term treatment of Graves' hyperthyroidism with ipodate: assessment of a minimal effective dose.

We have previously described that sodium ipodate (500 mg/day, p.o.) is effective in normalizing serum T3 and T4 levels in most patients with Graves' hyperthyroidism. In this study, we examined serum T3, T4, and rT3 levels in 14 hyperthyroid patients with Graves' disease during treatment with a lower dose (500 mg, every other day, p.o.) of sodium ipodate for a period of 3-30 weeks (mean 15.5 weeks). Three types of responses were observed. In group I (4 patients), both serum T3 and T4 were in the normal range at the end of treatment [baseline: mean +/- SEM T3, 6.8 +/- 0.96 nmol/L (normal 0.92-3.0)] and T4 [256 +/- 44 nmol/L (normal 62-167); post-ipodate: T3, 2.0 +/- 0.46 nmol/L and T4 107 +/- 28 nmol/L]. In group II (n = 5), either serum T3 (3 patients) or serum T4 (2 patients) did not become normal (baseline: T3 7.7 +/- 1.1 and T4 228 +/- 3.9; post-ipodate: T3 2.9 +/- 0.57 and T4 188 +/- 27 nmol/L). In group III (5 patients), neither serum T3 nor serum T4 returned to normal following ipodate treatment (baseline: T3 11.9 +/- 1.8 and T4 260 +/- 23; post-ipodate: T3 7.5 +/- 0.49 and T4 322 +/- 17 nmol/L). The mean serum rT3 concentration increased during ipodate treatment to a peak value of 100% above baseline and remained elevated (20-75% above baseline) throughout the study. Some improvement in hyperthyroidism was suggested by increase in body weight during ipodate treatment in most cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Thyroid function abnormalities associated with the chronic outpatient administration of recombinant interleukin-2 and recombinant interferon-alpha.

We prospectively examined thyroid function during and following chronic, outpatient therapy with recombinant interleukin-2 (rIL-2) and Roferon-A (rIFN-alpha 2a). Twenty-two of 30 patients with advanced renal cell carcinoma treated on a phase II open pilot study of concomitant rIL-2 and rIFN-alpha 2a were included. Serum levels of thyroxine, triiodothyronine, free thyroxine index, thyrotropin, antithyroid antibodies, and thyrotropin (TSH) receptor binding antibodies were measured before therapy and after every other cycle. Selected patients underwent studies after every cycle and following completion of therapy. Twenty patients (91%) developed laboratory evidence of thyroid dysfunction, 11 (50%) developed hypothyroidism, five (23%) had a biphasic pattern, and four (18%) had hyperthyroidism. The incidence of thyroid dysfunction increased with increased number of treatment cycles. Transient hyperthyroidism was noted in six of the 11 patients studied after the first cycle and persisted after cycle three in only two patients. Hypothyroidism was not observed after cycle 1, but became increasingly frequent between cycles 2 (56%) and 6 (90%). Thyroid function normalized following therapy in nine of 12 patients tested. Antithyroid antibodies were identified pretherapy in five patients (23%) and de novo in none; TSH receptor binding antibodies were not detected. This study demonstrates a remarkably high frequency of reversible thyroid dysfunction in patients with advanced renal cell carcinoma treated with repeated cycles of rIL-2 plus rIFN-alpha 2a. We conclude that chronic therapy with rIL-2 and rIFN-alpha 2a produces thyroid dysfunction in virtually all patients most likely secondary to a nonspecific, nonautoimmune, toxic manifestation of prolonged treatment. IL-2 therapy may, therefore, produce thyroid dysfunction by more than one mechanism.

Adult↗
PubMed1991

Postnatal changes in lambs of two pathways for thyroxine 5'-monodeiodination in brown adipose tissue.

We have recently shown that ovine fetal brown adipose tissue (BAT) contains two distinct iodothyronine 5'-monodeiodinase (5'MDI) activities, one with a high Km (type I) and another with a low Km (type II). Both activities increased to maximum levels near term (150 days gestation). BAT plays a major role in neonatal temperature regulation in lambs, and available evidence suggests that BAT 5'MDI activity is closely linked to thermogenic capacity. To better characterize the changes in 5'MDI after birth, we studied both type I and type II 5'MDI in lamb BAT from the time of birth to 30 days of postnatal age. Type I 5'MDI activity [pmol 3,5,3'-triiodothyronine (T3).mg protein-1.h-1] showed no significant changes during the first 11 days after birth [newborn (NB), 95 +/- 16; 1 day, 83 +/- 20; 3-4 days, 80 +/- 11; 10-11 days, 92 +/- 28]. Activity decreased significantly at 30 days (24 +/- 8.9, P less than 0.05). On the other hand, the type II 5'MDI activity (fmol I- released.mg protein-1.h-1) increased significantly (P less than 0.01) during the first 4 days, (NB, 348 +/- 23; 1 day, 679 +/- 37; 3-4 days, 785 +/- 199), decreased toward NB values (401 +/- 87) at 10-11 days of age, and fell to 66 +/- 31 at 30 days (P less than 0.05 vs. NB). Kinetic analysis of BAT type II thyroxine 5'MDI revealed a rise in maximum velocity from NB to 1 and 3-4 days of age without a change in the enzymatic activity Km.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗
PubMed1991

A study of the serum concentration of tumor necrosis factor-alpha in thyroidal and nonthyroidal illnesses.

We have studied serum concentrations of immunoassayable tumor necrosis factor-alpha (TNF alpha) and iodothyronines (T4, T3, and rT3) in normal subjects (n = 16) and patients with nonthyroidal illnesses (NTI; n = 13), hyperthyroidism (n = 10), and hypothyroidism (n = 9). The mean (+/- SEM; femtomoles per mL) serum concentration of TNF alpha was 45 +/- 4.3 in normal subjects, 84 +/- 38 in NTI, 54 +/- 6.0 in hyperthyroidism, and 50 +/- 10 in hypothyroidism; the various values did not differ significantly from one another. Serum TNF alpha was well within the normal range in all NTI patients, except one patient with a brain glioma and infection in whom it was elevated (540 fmol/mL). There was no significant correlation between serum TNF alpha and serum T4, T3, or rT3 levels in NTI patients. Similarly, there was no correlation between serum TNF alpha and serum thyroid hormone (T3 or T4) levels when data in normal subjects were combined with those in NTI patients. The dialyzable fraction of T3 and the free T3 concentration did not correlate with serum TNF alpha levels. However, there was a tendency toward a positive correlation between dialyzable fraction of T4 and the serum concentration of TNF alpha in NTI (r = 0.54; n = 11; 0.05 greater than P less than 0.1). The relationship between these two parameters became more clear when data in normal subjects and NTI patients were combined for statistical analysis (r = 0.59; n = 22; P less than 0.005). The free T4 concentration correlated positively with serum TNF alpha levels whether the data in NTI patients were analyzed alone (r = 0.93; P less than 0.001) or in combination with data from normal subjects (r = 0.85; P less than 0.001). Our data suggest that circulating TNF alpha may contribute to elevated free T4 in NTI. However, it is not a universal or common factor in the pathogenesis of other alterations in serum thyroid hormone levels in NTI (euthyroid sickness syndrome).

Adolescent↗
PubMed1990

American Thyroid Association guidelines for use of laboratory tests in thyroid disorders.

Selection of appropriate laboratory determinations will enable the clinician to diagnose thyroid dysfunction readily in the majority of patients. At the present time, estimation of free thyroxine and a "sensitive" thyrotropin assay are recommended as the principal laboratory tests for thyroid disease. A decrease in serum free thyroxine estimate and a raised level of serum thyrotropin confirm the diagnosis of hypothyroidism caused by thyroid gland failure. An increase in free thyroxine estimate combined with a serum sensitive thyrotropin level suppressed to less than 0.1 mU/L establishes the diagnosis of thyrotoxicosis. In sick patients, a normal or raised serum free thyroxine estimate together with a normal level of serum thyrotropin suggests that the patient has neither hypothyroidism nor thyrotoxicosis. Patients with severe illnesses, generally in the intensive care unit, and those treated with certain drugs, as well as individuals with unusual thyroid disorders, may present with confusing laboratory findings. An understanding of the regulation of the thyroid hormone system and/or judicious consultation with an endocrinologist should enable the clinician to diagnose thyroid disease, if present, in such patients.

Female↗
PubMed1990

Serum thyrotropin in hospitalized psychiatric patients: evidence for hyperthyrotropinemia as measured by an ultrasensitive thyrotropin assay.

In order to gather further insight into the basis for high serum T4 and/or T3 of psychiatric illnesses, we studied thyroid function in 84 consecutive newly hospitalized psychiatric patients (HPP) in a 12-week period. Serum T4 and T3 were measured by immunoassay and thyrotropin (thyroid-stimulating hormone [TSH]) by an ultrasensitive immunoradiometric assay. Serum T4 was in the normal range in 64 (76%) and elevated in 20 (24%); free T4 index was elevated in 13 of 75 (16%), total T3 in 12 of 60 (20%), free T3 index in seven of 56 (13%), and TSH in 14 of 84 (17%) cases so studied. Serum TSH was subnormal in only one case (1%). Among the 14 patients with elevated serum TSH, serum free T4 index was normal in 12 and elevated in two. High serum T4 (or free T4 index) and high serum TSH were not correlated significantly by chi 2 analysis. None of the patients with elevated TSH demonstrated goiter or antithyroglobulin or antimicrosomal antibodies. On repeat testing 7 to 21 days after admission, serum TSH (and/or T4) normalized in the three of five patients studied. Serum TSH response to 500 micrograms intravenous (IV) thyrotropin-releasing hormone (TRH) was normal (serum TSH post-TRH, 8 to 28 microU/mL) in two patients with elevated TSH and T4, one patient with normal TSH and high T4, and one patient with normal TSH and T4. One patient with suppressed serum TSH (0.1 microU/mL) had elevated serum T4 (16.9 micrograms/dL, normal 4.8 to 11.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Isolation of a hepatic iodothyronine 5'-monodeiodinase by nondenaturing agarose gel electrophoresis.

We have examined the application of nondenaturing agarose gel electrophoresis for isolation of the catalytically active iodothyronine 5'-monodeiodinase (5'-MD) in rat liver microsomes. Preliminary studies showed that most ingredients of conventional sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, including acrylamide, SDS, and bromophenol blue, markedly inhibited 5'-MD activity in solubilized rat liver microsomal proteins (SRLMP). We replaced these inhibitory components with those that had little or no inhibitory effect on the 5'-MD and devised conditions for nondenaturing agarose gel electrophoresis for isolation of a 5'-MD protein. SRLMP (up to 120 micrograms protein/well), prepared by preincubation with 5 mM 3-[(3-cholamidopropyl)dimethylammonio 1-propanesulfonate] (CHAPS) and 1% 2-mercaptoethanol, were subjected to electrophoresis in 0.35% agarose gel in 20 mM Tris-HCl, 10 mM EDTA, pH 6.6 buffer containing 2 mM CHAPS and 1 mM thioglycolic acid. Electrophoresis was carried out for 14 h at 4 C using 2.5 V/cm. After phoresis, the gel was sliced into 16 fractions, and homogenates of each fraction were tested for 5'-MD activity by incubation with 0.6 nM [125I]rT3 for 30 min at 37 C in the presence of 10 mM dithiothreitol. The peak 5'-MD activity was detected in fraction 6 (Rf, 0.375). This fraction accounted for about 30% of total 5'-MD activity and only 6% of protein in the gel. The gel slice containing the peak 5'-MD activity was next subjected to a second electrophoresis at pH 7.6 for 4 h in a 90 degrees different direction. The most 5'-MD activity was demonstrated in the third of 8 gel fractions. SDS-polyacrylamide gel electrophoresis of this fraction demonstrated only one 55 K protein in most experiments and occasionally an additional 35 K protein. The specific activity of 5'-MD in this fraction of greater than 11 pmol I-/mg protein.h was at least 2.3-fold that in SRLMP. Rabbits were immunized with agarose gel containing the peak 5'-MD activity. Immunized rabbit immunoglobulin G bound up to 70% of 5'-MD activity in SRLMP, and the binding effect varied in a dose-dependent manner. Western blot analysis revealed that the anti-5'-MD antibody bound only one 55 K protein among innumerable proteins in SRLMP. A specific antiprotein disulfide isomerase antibody bound a slightly larger, 57 K protein in SRLMP.(ABSTRACT TRUNCATED AT 400 WORDS)

Acrylamide↗
PubMed1990

Effect of amiodarone on non-deiodinative pathway of thyroid hormone metabolism.

Amiodarone, an iodine containing anti-arrhythmic drug, causes a significant decrease in molar ratio of daily production rates of T3 and T4 from 0.75 in controls to 0.36 in amiodarone-treated rabbits. A model was constructed from the above data which showed that metabolism of T4 via non-deiodinative pathways (e.g. tetraiodothyroacetic acid and/or conjugates) increased from 29% in untreated controls to 66% in amiodarone-treated rabbits. In this study, we have examined the metabolic clearance rate of tetraiodothyroacetic acid in rabbits given amiodarone (20 mg.kg-1.day-1 ip for 3 weeks) or saline (controls). Serum amiodarone and desethylamiodarone levels under the above experimental conditions were 0.20 +/- 0.067 and 0.17 +/- 0.058 mg/l, respectively, which were in the near-therapeutic range observed in humans. Control and amiodarone-treated rabbits were administered [125I]-tetraiodothyroacetic acid (10 muCi/rabbit) iv and blood was collected at 0.5, 1, 2, 4, 6, 10, 32 and 48 h. Serum tetraiodothyroacetic acid radioactivity was determined by trichloroacetic acid precipitation and ethanol extraction and metabolic clearance rates were calculated from the area under the curve of computer fits to tetraiodothyroacetic acid radioactivity data. Amiodarone treatment decreased metabolic clearance rates significantly from 0.107 +/- 0.008 in controls to 0.074 +/- 0.009 l/day in amiodarone-treated rabbits (p less than 0.05). However, when expressed per unit body weight (1.day-1.kg-1), the metabolic clearance rates were not significantly different between the controls and amiodarone-treated rabbits. The terminal serum elimination half-life in the two groups were similar (32.0 +/- 6.7 h in controls vs 49.2 +/- 12.4 h in amiodarone-treated).(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone↗