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At least 127 records · Page 7Linked to original sources
PubMed1993

X-ray crystal structure of the Ala-109-->Thr variant of human transthyretin which produces euthyroid hyperthyroxinemia.

The structure of the Ala-109-->Thr mutation of human transthyretin, a nonamyloidogenic variant with enhanced thyroxine binding, has been determined by x-ray diffraction to a resolution of 1.7 A. The model, including 175 solvent water molecules, has been refined by constrained least squares to an R-value of 0.157. The standard deviations for protein geometry are 0.016 A for bond distances, 0.5 degree for bond angles, 0.031 A for 1-4 distances, and 0.005 A for deviations of planar groups from their least squares plane. The estimated error in protein atomic coordinates is 0.12 A. Residue 109 extends inward between the two beta sheets which form the major component of the monomer, as does the side chain of residue 30 in the amyloidogenic Met-30 variant. Comparison of the Thr-109 structure with that of the normal shows that the extra atoms of the threonine fit into empty space between sheets and make no extensive changes to the molecular conformation. The substitution at 109 causes small local changes in the secondary structure of the A, G, and H strands resulting in a shift of residues 15-17, 108-110, and 117 in each monomer. The thyroxine-binding sites of the Thr-109 and Met-30 variants and of the normal protein are compared, and the results suggest that the variation in affinity for thyroxine between the three proteins may arise from differences in the size of the binding pocket.

Binding Sites↗
PubMed1982

Hyperthyroxinemia in patients with acute psychiatric disorders.

Thyroid function tests were measured in 645 patients admitted to an acute psychiatric disorders unit. Thirty-three percent had elevated serum thyroxine (T4), and 18 percent had an elevated free T4 index (FTI). Serum triiodothyronine (T3) was low, normal, or minimally elevated in 77 patients, with a high initial free T4 index. Twenty-two patients with an initial elevation of their free T4 index were serially followed (study group). Serum T4, free T4 index, and free T4 fell in every patient: serum T4 from 13.95 +/- 1.93 micrograms/dl (mean +/- standard deviation: SD) to 9.33 +/- 2.4 micrograms/dl (p less than 0.001); free T4 index, from 6.15 +/- 0.83 to 3.79 +/- 1.1 (p less than 0.001); free T4, from 2.43 +/- 0.65 mg/dl to 1.38 +/- 0.35 ng/dl (p less than 0.001). Serum T3 was initially normal or low, and then fell in 17 patients, and rose in five. Serial testing of thyrotropin-releasing hormone (TRH) demonstrated both flat and normal responses in patients with a variety of psychiatric diagnoses and at varying stages of thyroid disease activity.

Acute Disease↗
PubMed1985

[Post-traumatic hyperthyroxinemia or hyperthyroidism].

A fifteen year-old girl presented with several fractures after a road traffic accident. Five days later, fat embolism occurred, complicated by adult respiratory distress syndrome (ARDS) and disseminated coagulation (DIC). She was successfully managed in the intensive therapy unit, and was transferred to a general surgery after five weeks. Tachycardia and fever persisted without any other sign of infection. Clinical examination showed exophthalmos and a thyroid murmur. The venous concentration of T4 was increased: 204 nmol . 1(-1) (N: 70-150), whereas that of T3 was normal: 2.3 nmol . 1(-1) (N: 1-1.25). No other investigations were performed. The regression of clinical symptoms and a normalization of T4 were seen after treatment (carbimazole and acebutolol). Post-traumatic hyperthyroidism is discussed. Although classical, this syndrome was not well documented, as was shown in the literature survey. After trauma or an acute illness, an early fall in thyroid hormone concentrations was usually seen; a late increase in T4 was a rare occurrence.

Adolescent↗
PubMedDate not supplied

Hyperthyroxinemia and hypotriiodothyroninemia with clinical euthyroidism.

A clinically euthyroid woman had substernal goiter and thrombocytopenia. There was a striking elevation in serum thyroxine (T4) level when the level of triiodothyronine (T3) ws low, reverse T3 (rT3) was normal I131 uptake was suppressed, and thyroid stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) was blunted. The elevation of T4 was transient and required no treatment. Postmortem examination revealed a thyroid gland that showed only multinodular goiter. Multiple factors contributed to the dissociation between T4 and T3 levels. There was a lack of clinical symptoms in the face of high T4 and normal T3. The report stresses the need for thorough evaluation of thyroid function in such cases before instituting treatment.

Aged↗
PubMed1988

Suckling, but not formula feeding, induces a transient hyperthyroxinemia in rat pups.

To assess the effect of breast feeding on circulating thyroid hormone levels in the suckling neonate, we examined serum concentrations of T4, T3, and rT3 by RIA in 12- and 15-day-old rat pups fasted for 3 or 6 h before, at, and hourly for 3 or 4 h after suckling. In both age groups, serum T4 levels decreased significantly in response to the 6-h fast; no significant differences were observed after 3 h. T3 levels in 15-day-old (but not 12-day-old) rats were likewise significantly depressed, and rT3 levels were higher relative to those in the prefast group. After a 90-min suckling period, serum total and free T4 concentrations of 12-day-old pups increased 1 h postsuckling to levels significantly higher than those in the fasted animals; maximum levels were achieved at 2 h. T3 levels were unchanged over this period. In contrast, elevated total and free T4 and T3 levels and a reciprocal decrease in rT3 concentration, were evident immediately after the 90-min suckling period (0 h) in 15-day-old rat pups and increased through 1 h to levels significantly higher than those in the prefast group. After refeeding (0 h) of 3-h fasted pups, serum T4 levels increased significantly over fasted levels in suckled 12- and 15-day-old rats, as did T3 levels in 15-day-old pups, through 2 h postsuckling. In contrast, thyroid hormone levels of pups gavage-fed a commercial formula preparation at no time exceeded those of the prefast groups at either age, despite highly comparable stomach weights for both formula-fed and suckled pups at the time of refeeding. We conclude that 1) rat pups between the ages of 12 and 15 days postpartum become hypothyroxinemic between 3 and 6 h of milk deprivation, and 2) this condition is reversed by significant increases in T4 and T3, rendering the animal transiently hyperthyroxinemic after suckling, but not in response to formula feeding. Our data further demonstrate the critical nature of study designs involving fasts (either planned or incidental) of suckling rats in light of the observed pronounced variations in their thyroid hormone status relative to time postsuckling.

Animal Feed↗
PubMed1981

Hyperthyroxinemia with bradycardia and normal thyrotropin secretion after chronic amiodarone administration.

Pituitary-thyroid function was tested in 15 euthyroid patients before, during, and after long term oral treatment with amiodarone (2-n-butyl-3,4'-diethylaminoethoxy-3',5'-diiodobenzoylbenzofurane; 600-1200 mg daily), an iodine-containing potent antiarrhythmic drug. The drug caused increases in serum total T4, free T4, and rT3, with a concomitant decrease in T3. Baseline serum TSH was significantly higher after 1 week of drug treatment and returned to normal levels after 12 weeks of treatment. All patients receiving amiodarone had a slowing of their heart rate (P less than 0.01), and heart rate gradually increased 6 weeks after drug withdrawal, concurrent with the slow fall in T4 and rT3 levels. Amiodarone did not cross-react in the iodothyronine RIAs. The results suggest that amiodarone inhibits the peripheral conversion of T4 to T3 and may block the metabolic action of thyroid hormone in man.

Aged↗