Inner ring monodeiodination of thyroxine and 3,5,3'-L-triiodothyronine in rat brain.

To elucidate the metabolism of thyroid hormone in the central nervous system (CNS), 5-monodeiodinating activities were studied by incubating T4 or T3 with an aliquot of the P2 fraction of the rat brain in the presence of dithiothreitol and measuring the amounts of rT3 or 3,3'-L-diiodothyronine (3,3'-T2) produced by RIA. The production of rT3 or 3,3'-T2 was dependent upon duration of the incubation, amount of tissue used, temperature, and pH (the optimal pH was 8.0). These findings show that these reactions are enzymic in nature. For the conversion of T4 to rT3, the Km was estimated to be 1.33 microM, and the Vmax was 173 fmol/mg protein . min. For the conversion of T3 to 3,3'-T2, the Km was estimated to be 2.31 microM, and the Vmax was 94 fmol/mg protein . min. Both the conversion of T4 to rT3 and that of T3 to 3,3'-T2 were dependent on the concentration of dithiothreitol, but were not inhibited by propylthiouracil, the well known inhibitor of 5'-deiodinating activity. Both activities were mainly found in the synaptosomal fractions. The P2 fraction from fetal and neonatal rat brains had significantly higher activity than that from the adult brain. These findings demonstrate the presence of 5-monodeiodinating activities in the rat brain.

High affinity 3,5,3'-L-triiodothyronine binding to synaptosomes in rat cerebral cortex.

Studies were undertaken to define the existence of specific T3-binding sites in the synaptosomal fraction of rat cerebral cortex. Development-related changes of the synaptosomal T3-binding sites were compared with those of nuclear T3 receptors in rat cerebral cortex. Scatchard analysis was compatible with the existence of two sets of high affinity T3-binding sites: K1, with a mean (+/- SE) apparent dissociation constant (Kd) of 3.22 +/- 0.63 x 10(-11) M and a mean (+/- SE) maximum binding capacity (MBC) of 3.2 +/- 0.3 pg T3/mg protein, and K2, with a K4 of 2.64 +/- 0.15 x 10(-9) M and a MBC of 218.3 +/0 15.0 pg T3/mg protein. When compared to T3, 27-, 135-, 500-, and 1000-fold higher concentrations of T4, 3,5-diiodothyronine (3,5-T2), triiodothyroacetic acid, and rT3, respectively, were needed to obtain 50% depression of the synaptosomal T3 binding. Tetraiodothyroacetic acid, 3,3'-T2, 3'5'-T2, 3-monoiodothyronine (3-T1), 3'-T1, and thyronine had little effect. The MBC of T3 nuclear receptors was the highest at 2 days of age and significantly decreased thereafter, although an almost constant K4 was observed in all age groups studied. On the contrary, the MBC of the higher affinity synaptosomal T3-binding sites was low in 2-day-old rats (20.3 +/- 1.2 pg T3/g tissue) and increased thereafter to the level in young adult ras (50.4 +/- 2.2 pg T3/g tissue). However, the Kd of synaptosomal T3-binding sites was also unchanged in all age groups studied. These findings clearly indicate that there exist specific T3-binding sites in synaptosomes from rat cerebral cortex.

Triiodothyronine generation from thyroxine in human thyroid: enhanced conversion in Graves' thyroid tissue.

Conversion of T4 to T3 was studied in normal, Graves', and neoplastic thyroid tissues obtained at surgery. Homogenates of human thyroid follicular adenoma and carcinomas were incubated with [125I]T4 and dithiothreitol (DTT) at 37 C for 60 min under N2 gas. T3 formation was assessed by measuring [125I]T3 formed, using paper chromatography. In the second series of experiments, the suspensions of the 100,000 X g pellet of normal thyroid tissues adjacent to the tumor and Graves' thyroid tissues were incubated with unlabeled T4 and DTT at 37 C for 60 min under N2 gas. T3 generated was measured by RIA. T3 generation in the thyroid tissue was dependent on incubation time, amount of the tissue used, concentration of DTT, temperature, and pH. Propylthioracil inhibited T3 formation, while methimazole had no effect. A kinetic study with the homogenate of a thyroid adenoma and 100,000 X g pellet suspensions of two normal and three Graves' thyroids gave apparent Km values of 2.7, 4.9, and 4.1 microM for T4, respectively, and Vmax values of 0.8, 3.0, and 10.9 pmol T3/mg protein.min, respectively. Conversion of T4 to T3 was observed in two of three tumor tissues studied and was markedly enhanced in Graves' thyroid tissues (mean +/- SE, 11.9 +/- 2.0 pmol/mg protein.min) compared to that of normal thyroid tissues (3.2 +/- 0.6 pmol/mg protein.min; P less than 0.01). It is concluded that T4 is enzymatically converted to T3 in normal and Graves' thyroids and differentiated thyroid neoplasms. Moreover, enhanced conversion of T4 to T3 was found in Graves' thyroid tissue.

Age-related changes of serum 3,3'-diiodothyronine, 3',5'-diiodothyronine, and 3,5-diiodothyronine concentrations in man.

To evaluate the effects of aging on T4 metabolism, serum 3,3'diiodothyronine (3,3'-T2), 3',5'-diiodothyronine (3',5'-T2), and 3,5-diiodothyronine (3,5-T2) as well as T4, T3, and rT3 concentrations were determined by RIAs in 81 normal subjects, aged 24-81 yr. 3,3'-T2, 3',5'-T2, and 3,5-T2 antisera were prepared by immunizing rabbits with the protein conjugate of each diiodothyronine. Since the 3',5'-T2 antiserum cross-reacted with rT3 to the extent of 1.8%, correction was made by subtracting 1.8% of the rT3 value from the measured 3',5'-T2 value. The other 2 antisera had no noticeable cross-reactivity with various thyroid hormone derivatives. Although no significant relation existed between T4 levels and age (r = -0.14; P greater than 0.1) serum T3 showed a significant correlation with age (r = -0.28; P less than 0.05). In contrast, no significant correlation was observed between rT3 and age (r = 0.12; P greater than 0.1). Serum 3,3'-T2, 3',5'-Tw, and 3,5-T2 values (nanograms per dl) all had significant inverse correlations with age, the coefficients of correlation being -0.38 for 3,3'-T2 (P less than 0.01), -0.58 for 3',5'-Tw (P less than 0.01), and -0.47 for 3,5-T2 (P less than 0.01). These findings suggest that sequential monodeiodinating activities in T4 metabolism decrease with increasing age.

Induction of outer and inner ring monodeiodinases in human thyroid gland by thyrotropin.

The effects of TSH on iodothyronine 5- and 5'-deiodinations were investigated using cultured thyroid tissues from patients with Graves' disease. The addition of TSH to the culture medium stimulated all of the iodothyronine-deiodinating activities of thyroid tissues cultured for more than 4 days. Peak TSH-induced activities were found on the fifth day of culture, and increased activities were found up to 9 days. On the fifth day of culture, TSH enhanced both outer and inner ring monodeiodinations in a dose-responsive manner between 62.5 and 250 microU/ml. This stimulation by TSH was blocked by the addition of actinomycin D or propylthiouracil. Incubation of thyroid tissues with (Bu)2cAMP mimicked the action of TSH, and theophylline potentiated the action of TSH. These results suggest that TSH, in an action probably mediated by cAMP, induces synthesis of iodothyronine deiodinases in the thyroid gland.

3,3',5'-triiodothyronine (reverse T3) in human cerebrospinal fluid.

To examine the metabolic products of thyroid hormones in the central nervous system, total and free rT3 as well as T4 in human cerebrospinal fluid (CSF) were determined in 41 patients. Total T4, T3, and rT3 concentrations in CSF were determined by RIA, and free T4, T3, and rT3 fractions were analyzed by the magnesium precipitation method. The mean (+/- SE) total T4 and T3 concentrations in CSF were 166 +/- 24 and 2.6 +/- 1.5 ng/dl, respectively; the values were approximatey 2% of those in normal control pooled sera. Total rT3 concentrations in CSF from 29 clinically euthyroid patients who were apparently in a normal nutritional state ranged from 5.2-23 ng/dl (mean +/- SE, 11.2 +/- 0.9 ng/dl); the value was approximately 40% of that in sera. A patient with primary hypothyroidism had a markedly diminished CSF rT3 concentration (1.1 ng/dl), and the remaining 11 patients, suffering from severe diseases such as meningitis and cerebrovascular accident, had significantly higher CSF rT3 concentrations (37.5 +/- 6.6 ng/dl) than the clinically euthyroid patients. Although free T4 and T3 concentrations in CSF (5.9 +/- 1.1 and 0.16 +/- 0.05 ng/dl, respectively) were similar to those in serum (2.1 +/- 0.2 and 0.22 +/- 0.01 ng/dl, respectively), the free rT3 concentration in CSF (0.70 +/- 0.12 ng/dl) was approximately 20 times higher than that (0.044 +/- 0.016 ng/dl) in serum. Furthermore, the reciprocal relationship was observed between CSF total rT3 concentrations and free rT3 percentages in CSF. These data suggest the possibility that rT3 may be produced from T4 in human brain and that there may be a transport mechanism regulating free rT3 in CSF.

Sequential deiodination of thyroxine in human thyroid gland.

The inner ring monodeiodination [T4 to rT3, T3 to 3,3'-diiodothyronine(3,3'-T2)] as well as the outer ring monodeiodination (T4 to T3, rT3 to 3,3'-T2) was demonstrated with thyroid tissues obtained from patients with Graves' disease by measuring the products by RIAs. Sequential deiodination of T4 to 3,3'-T2 was also recognized in normal human thyroid glands. These iodothyronine deiodinations were dependent on incubation time, tissue volume, temperature, pH, and concentration of dithiothreitol. The monodeiodination of rT3 to 3,3'-T2 proceeded very rapidly and the maximal production of 3,3'-T2 was obtained at about 5 min. In the other reactions, the products accumulated in an almost linear fashion during the period of 60 min. The optimal pH for 5-monodeiodination was 9.0, while that for 5-monodeiodination was 5.5-6.5. In the absence of dithiothreitol, all of these reactions were abolished. Propylthiouracil and iopanoic acid inhibited the reactions, whereas methimazole and potassium iodide had no effect. Kinetic study revealed that the apparent Km and maximum velocity of the conversion of T3 to 3,3'-T2 were 10.9 microM and 19 pmol 3,3'-T2/mg protein.min, respectively, and that those of rT3 to 3,3'-T2 were 0.37 microM and 80 pmol 3,3'-T2/mg protein.min, respectively. There was a significant difference in the conversion of T4 to rT3 between normal [0.56 +/- 0.04 pmol/mg protein.min (mean +/- SE)] and Graves' thyroids 0.88 +/- 0.06 pmol/mg protein min). Moreover, a significant difference was found between 3,3'-T2 production rate from T3 or rT3 in the Graves' thyroids and that in the normal thyroids. The overall reaction from T4 to 3,3'-T2 in the Graves' thyroids (4.04 +/- 0.70 pmol/mg protein.min) was significantly higher than that in the normal thyroids (0.63 +/- 0.11 pmol/mg protein.min; P less than 0.001). The results indicate the existence of 5-deiodinase that produces rT3 from T4 and 3,3'-T2 from T3, and 5'-deiodinase that produces T3 from T4 and 3,3'-T2 from T3, and 5'-deiodinase that produces T3 from T4 and 3,3'-T2 from rT3 in human thyroids. Accelerated conversion of T4 to 3,3'-T2 via either T3 or rT3 was observed in Graves' thyroid glands.

Graves' hyperthyroidism following transient thyrotoxicosis during interferon therapy for chronic hepatitis type C.

We report a case of Graves' hyperthyroidism induced by long-term interferon (IFN) therapy. A 52-year-old woman suffered from chronic active hepatitis type C and was treated with a total of 456 x 10(6) units of IFN-alpha for 23 weeks. During the 12th week of treatment she showed transient thyrotoxicosis. One week after the termination of IFN therapy, TSH-receptor antibodies became positive and subsequently she showed Graves' hyperthyroidism. This case showed sequential manifestation from transient thyrotoxicosis to the appearance of TSH-receptor autoantibodies, and then the occurrence of Graves' hyperthyroidism during IFN therapy. The course of this case may be useful in the understanding of the pathogenesis of autoimmune hyperthyroidism.

Primary aldosteronism with bilateral multiple aldosterone-producing adrenal adenomas.

A 41-year-old woman developed primary aldosteronism due to bilateral multiple aldosterone-producing adenomas (APA). She was suspected to have idiopathic hyperaldosteronism (IHA) 7 years previously. Although preoperative data suggest APA and IHA was suspected in a postoperative microscopic specimen, a definite clinical diagnosis could not be made. Cytochrome P-450 and other enzymes involved in aldosterone synthesis were found in the tumor portions but not in the zona glomerulosa of attached adrenals, which histopathologically showed "paradoxical hyperplasia". This was a rare case of bilateral multiple APA, which could be differentiated from IHA by immunohistochemical analysis of adrenal steroidogenic enzymes.

Sex- and age-related changes of exophthalmos in graves' disease.

In order to evaluate the effect of sex and age on the protrusion of the eyes in patients with Graves' disease, exophalmometry was performed on 95 patients, aged 16-73. The mean (+/- SE) protrusion in the 190 eyes was 17.5 +/- 0.2 mm, being significantly higher than those in normal subjects (14.9 +/- 0.2 mm) and patients with Hashimoto's disease (14.3 +/- 0.2 mm). No significant difference existed in the degree of protrusion between thyrotoxic Graves' disease patients and those maintained in an euthyroid state during treatment with antithyroid drugs. When compared in terms of the duration of the treatment, the protrusion became prominent with the increased duration of the treatment, especially in male patients, although statistically not significant. The protrusion in male patients tended to increase, though not significantly, with increasing age, whereas it decreased significantly with increasing age in female patients.

Modulation of T4 5'-monodeiodination in rat anterior pituitary and liver homogenates by thyroid states and fasting.

In order to clarify the role of the pituitary conversion of L-thyroxine (T4) to 3, 5, 3'-L-triiodothyronine (T3) in regulating thyrotropin (TSH) secretion, the effect of altered thyroid states and fasting on intrapituitary T3 generation was investigated by a paperchromatographic procedure using the anterior pituitary homogenates. Hepatic T3 generation was also studied for comparison. The rate of pituitary and hepatic T3 generation in normal rats averaged 25.2 +/- 12.4 (mean +/- SE) fmoles T3/mg protein/min and 33.8 +/- 12.7 fmoles T3/mg protein/min, respectively. T4 treatment raised the hepatic T3 generation from T4 (46.7 +/- 3.1 fmoles T3/mg protein/min) and lowered the intrapituitary T3 generation (4.5 +/- 0.2 fmoles T3/mg protein/min). On the contrary, thyroidectomy slowed the hepatic T4 5'-deiodination (11.0 +/- 2.8 fmoles T3/mg protein/min), and accelerated the pituitary T4 5'-deiodination (64.3 +/- 1.4 fmoles T3/mg protein/min). In 48 h fasted rats, serum T4, T3 and TSH concentrations were all lower than those in fed rats, and both pituitary and hepatic T3 generations were also suppressed. Thus, altered thyroid states cause an opposite effect on pituitary and liver 5'-monodeiodination, whereas fasting causes similar changes. The findings suggest the existence of an autoregulatory mechanism for thyroid hormone activation within the target tissues.

Reciprocal relation between serum thyrotropin levels and intrapituitary 3,5,3'L-triiodothyronine generating activity from thyroxine in perinatal rats.

Thyroxine (T4) 5'-monodeiodinating activity in rat pituitary was studied, using paper chromatography. Rat anterior pituitary homogenates were incubated with 125I-T4, dithiothreitol and unlabeled L-T4 at 37 degrees C. The incubation mixture was extracted by ethanol and the extracts were subjected to descending paper chromatography. The conversion ratio of T4 to 3, 5, 3'L-triodothyronine (T3) was calculated from the radioactivity of T3 spot to total radioactivity on the paper strip. The T3 amount generated was estimated from the T4 concentration in the incubation mixture and the conversion ratio. The T3 generating activity from T4 increased as the amount of tissue increased. It was temperature-and pH-dependent, and thiol sensitive. These results suggest the enzymatic nature of T4 5'-monodeiodinating activity of the anterior pituitary. A kinetic study revealed low Km for T4 (7.9 +/- 1.6 nM, Mean +/- SE), with Vmax of 68.0 +/- 12.7 fmoles T3/mg protein/min. T4 monodeiodinating activity was consistently, though minimally, detected in fetal rat pituitaries and increased after birth, reaching the maximum at 22 days. It declined thereafter to the young adult level. Serum TSH levels were markedly elevated in fetus. They decreased after birth, reaching the nadir at 22 days, and then increased to young adult levels. Serum T4 and T3 levels were markedly diminished in fetus and gradually increased after birth, reaching the young adult levels at 17 days. Thus, a reciprocal relationship was observed between intrapituitary T3 generating activity from T4 and serum TSH levels in developing rats. It suggests that the conversion of T4 to T3 in the pituitary plays a role in regulating TSH secretion.

Treatment of hyperthyroidism with a small single daily dose of methimazole.

A prospective randomized trial with the conventional divided doses (10 mg 3 times daily, N = 29) and a small single daily dose (15 mg once daily, N = 25) of methimazole for the treatment of Graves' hyperthyroidism was performed. Within 8 weeks, almost 80% of the patients in both groups became euthyroid. The mean time required to achieve the euthyroid state was 6.0 +/- 2.8 and 6.0 +/- 3.8 weeks, respectively. TSH binding inhibitor immunoglobulin was found in about 90% of the patients in both groups before methimazole treatment. However, a gradual fall of its levels was observed in nearly all patients after treatment. There was no difference in the mean levels of TSH binding inhibitor immunoglobulin between the two groups during therapy. We conclude that the single daily dose regimen of 15 mg of methimazole will control Graves' hyperthyroidism in most patients, and TSH binding inhibitor immunoglobulin levels decrease in this regimen in the same way as with the conventional divided dose regimen (10 mg 3 times daily).

Serum concentrations of 3, 3'-diiodothyronine, 3', 5'-diiodothyronine, and 3, 5-diiodothyronine in altered thyroid states.

To investigate the thyroid hormone metabolism in altered states of thyroid function, serum concentrations of 3, 3'-diiodothyronine (3, 3'-T2), 3', 5'-T2 and 3, 5-T2 as well as T4, T3 and rT3 were determined by specific radioimmunoassays in 17 hyperthyroid and 10 hypothyroid patients, before and during the treatment. Serum T4, T3, rT3, 3, 3'-T2 and 3', 5'-T2 concentrations were all higher in the hyperthyroid patients than in age-matched controls and decreased to the normal ranges within 3 to 4 months following treatment with antithyroid drugs. In the hypothyroid patients, these iodothyronine concentrations were lower than in age-matched controls and returned to the normal ranges after 2 to 3 months treatment with T4. In contrast, serum 3, 5-T2 concentrations in hyperthyroid patients (mean +/- SE : 4.0 +/- 0.5 ng/dl) were not significantly different from those in controls (3.9 +/ 0.4 ng/dl), although they tended to decrease in 3 of 6 patients after the antithyroid drug therapy. Serum 3, 5-T2 levels in the hypothyroid patients (3.8 +/- 0.6 ng/dl) were also within the normal range and showed no significant change following the T4 replacement therapy. However, serum 3, 5-T2 as well as 3, 3'T2 concentrations rose significantly with a marked rise in serum T3 following T3 administration, 75 micrograms/day for 7 days, in Graves' patients in euthyroid state.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of rT3 5'-monodeiodination in rat brain: comparison with T4 and T3 5-monodeiodinations.

The present study revealed the existence and some characteristics of rT3 5'-deiodinase in rat brain by measuring the production of 3,3'-T2 from rT3 by radioimmunoassay. The conversion of rT3 to 3,3'-T2 was dependent on the duration of the incubation, tissue amount, temperature and pH (the optimal pH was 8.0), suggesting its enzymatic nature. Apparent Km was estimated to be 0.16 microM and the Vmax was 139.3 fmol/mg protein/min. The converting activity was dependent on the concentration of dithiothreitol (DTT). In contrast to T4 or T3 5-deiodinase, rT3 5'-deiodinase activity in the rat brain was the highest in cerebellum and the activity was low in the neonatal rat brain. Moreover, the 5'-deiodinase activity was inhibited by propylthiouracil (PTU). These differences between rT3 5'-deiodinase and T4 or T3 5-deiodinase suggest that different deiodinases are present in rat brain, and the local conversion of thyroid hormone is important for its action in the central nervous system.

Cushing's syndrome associated with corticogenic hypothyroidism: a case study.

Described here is a 27-year-old female, who had centripetal obesity, broad reddish-purple striae on the lower abdomen and hypertension. Serum cortisol levels, the results of a dexamethasone suppression test and an adrenal scintigram with 131I-19-iodocholesterol were all compatible with Cushing's syndrome due to an adrenal adenoma that secretes cortisol autonomously. This was confirmed by gross and microscopic examination of the removed adrenal tumor. In addition, the patient had markedly diminished T4 and T3 concentrations in serum. Basal TSH levels were not elevated and did not rise significantly after TRH injection. Serum T4 and T3 concentrations were elevated to the normal range when the hyperadrenocorticism was corrected. The results indicate that the patient had "'corticogenic hypothyroidism."

Treatment of hyperthyroidism with a small single daily dose of methimazole: a prospective long-term follow-up study.

A prospective long-term follow-up study was performed with conventional divided doses (group C: 10 mg 3 times daily, N = 58) and a small single daily dose (group S: 15 mg once daily, N = 54) of methimazole (MMI) for the treatment of Graves' hyperthyroidism. Within 8 weeks, almost 80% of the patients in both groups became euthyroid. The mean time required to achieve a euthyroid state was 5.6 +/- 2.7 weeks in group C and 5.8 +/- 3.1 in group S. TSH binding inhibitor immunoglobulin (TBII) levels before therapy were 44.2 +/- 22.7% and 47.1 +/- 23.9% in group C and group S, respectively. A similar gradual fall in TBII levels was observed in both groups over a two-year period of treatment. MMI doses were gradually reduced to a maintenance dose (5 mg daily) after the patients became euthyroid. The patients were treated for 28 +/- 9 months and were followed up after therapy was stopped (observation period in patients who remained in remission was 12-130 (75 +/- 34) months and the interval to relapse in recurred cases was 1-98 (20 +/- 27) months). The rates of recurrence in group C were 41% at 1 yr, 54% at 2 yrs, 56% at 4 yrs and 61% at 6 yrs. In group S, these were 44%, 53%, 56% and 63%, respectively. No differences between relapse rates were observed with the two different dosage regimens. Adverse effects occurred more frequently in group C patients (24%) than in group S patients (13%). These results show that there is no difference in the clinical and immunological course or in the long-term remission rate of Graves' hyperthyroidism when the treatment is initiated with either a small single daily dose (15 mg) or the conventional regimen (10 mg 3 times daily).

Synaptosomal T3 binding sites in rat brain: their localization on synaptic membrane and regional distribution.

Previous studies have shown the existence of specific high affinity T3 binding sites in rat cerebrocortical synaptosomes. In this study, to define the localization of the binding sites, T3 binding to disrupted synaptic membrane fractions was compared with the binding to intact synaptosomes obtained from the rat cerebral cortex. Scatchard analysis revealed two orders of T3 binding sites with almost identical apparent dissociation constant (Kd) in synaptosomes and synaptic membrane fractions. However, the maximal binding capacity (MBC) of the higher affinity binding sites for synaptic membrane fractions was significantly greater than that for intact synaptosomes (4.2 +/- 0.2 vs 3.0 +/- 0.3 pg T3/mg protein). Regional distribution of the synaptosomal T3 binding sites in various areas of the rat brain was also studied. The Kd values were not significantly different in discrete brain regions. On the other hand, the MBCs of the higher affinity binding sites were greater in the cerebral cortex and hypothalamus (72.8 +/- 1.4 and 64.8 +/- 9.5 pg T3/g tissue) than in the cerebellum (22.1 +/- 1.6 pg T3/g tissue). Similar difference was also observed in the lower affinity sites. These results indicate that the specific T3 binding sites in brain synaptosomes are localized mainly on synaptic membranes and that the MBC is different in discrete brain regions.

Primary aldosteronism associated with a primary double cancer of the thyroid and rectum: report of a case.

A variety of complications are encountered in primary aldosteronism. Among them, less well known is the association of functioning adrenocortical adenoma with neoplasia of other organs. Described here is a patient with primary aldosteronism who had undergone a surgical operation for thyroid cancer and died of meningoencephalitis due to Listeria monocytogenes. Moreover, the autopsy revealed that he had an adenocarcinoma of the rectum. To our knowledge, this is the first documented case of a patient who had both primary aldosteronism and a primary double cancer of the thyroid and rectum.