T3 Suppression Research Articles

Endocrine, Biochemical, and Morphlogical Studies of a Pituitary Adenoma Secreting Growth Hormone, Thyrotropin (TSH), and α-Subunit: Evidence for Secretion of TSH with Increased Bioactivity*

A 40-yr-old man who had acromegaly and hyperthyroidism due to a GH/TSH-secreting pituitary adenoma is described. Serum free T4 was 2.8 ng/dl, free T3 was 1.1 ng/dl, and TSH was 1.2-1.5 microU/ml; the latter was measured in an immunoradiometric assay with a sensitivity of 0.07 microU/ml. Serum TSH was immunologically identical to standard TSH and did not decrease during a T3 suppression test. Serum free alpha-subunit and the molar alpha-subunit to TSH ratio were high (6.1 ng/ml and 31.2, respectively). TRH administration induced significant increases in both GH (+129%) and alpha-subunit (+156%) levels. Conversely, dopamine infusion resulted in a decrease in serum GH (-66%) and alpha-subunit (-43%) levels, and subsequent administration of the dopamine antagonist sulpiride induced significant increases in both GH and alpha-subunit (+393% and +106%, respectively). Similarly, somatostatin infusion inhibited GH (-43%) and alpha-subunit (-61%) secretion. Serum TSH levels were not affected by TRH, dopamine, or somatostatin. The biological to immunological activity ratio of serum TSH purified by immunoaffinity chromatography and measured in an adenylate cyclase assay was significantly increased compared to that in serum from hypothyroid or euthyroid subjects [biological to immunological activity ratio, 6.9 +/- 0.2 (+/- SD) vs. 4.4 +/- 1.1; P less than 0.001]. In gel chromatography, the apparent mol wt of the patient's TSH was smaller than that of the controls. After adenomectomy, all of the altered parameters of pituitary function became normal. Double gold particle immunostaining of the adenomatous tissue showed that all of the cells contained secretory granules positive for GH and alpha-subunit, while very few cells were positive for TSH beta as well as GH and alpha-subunit. These data indicate that in this patient serum TSH had an apparent mol wt smaller than that of normal TSH and an increased biological activity which, along with the autonomous TSH secretion, account for hyperthyroidism in the presence of low normal TSH levels; alpha-subunit originated from the same adenomatous cells that secreted GH but not TSH, thus explaining the in vivo observation that alpha-subunit responses to several agents were dissociated from TSH responses and parallel to GH responses; and TSH and GH were colocalized in a minority of the neoplastic cells.

Regulation of thyrotropin secretion by the central epinephrine system. Studies in the chronically cannulated rat.

In the present investigation CNS epinephrine (EPI) biosynthesis was selectively interrupted with specific norepinephrine N-methyltransferase (NMT) inhibitors, SK&F 64139 (Smith, Kline & French Laboratories) and LY 78335 (Eli Lilly & Co. Research Laboratories), to determine the effects of central EPI depletion on basal and cold, thyrotropin-releasing hormone, and hypothalamic somatostatin antiserum induced thyrotropin (TSH) secretion in chronically cannulated rats. Because these NMT inhibitors also are alpha 2-adrenergic receptor blockers, the effects of alpha 2- and alpha 1-adrenergic blockade and alpha 2-activation on plasma TSH were assessed with rauwolscine and corynanthine and B-HT 933, respectively. Serum T4 and plasma corticosterone were also measured. Blockade of CNS EPI synthesis resulted in inhibition of basal and cold and thyrotropin-releasing hormone induced TSH release, suppression of serum T4, and increased corticosterone release. The stimulatory effect of SRIF antiserum on plasma TSH was not altered by SK&F 64139. alpha 2-adrenergic blockade suppressed plasma TSH levels, but not to the same degree as the NMT inhibitors; activation of alpha 2-receptors enhanced TSH secretion. Thus, it is possible that part of the effect of the NMT inhibitors on TSH was due to alpha 2-blockade. alpha 1-adrenergic blockade also lowered plasma TSH. These results indicate that central EPI systems have a stimulatory role in TSH regulation, possibly mediated by alpha 2-adrenergic receptors, cold-induced TSH release is mediated, in part, by EPI, and central EPI systems exert an inhibitory effect on the hypothalamic-pituitary-adrenal axis.

Thyroid Function and Histology in Forty-Five Patients with Hyperthyroid Graves' Disease in Clinical Remission More Than Ten Years after Thionamide Drug Treatment

Thyroid function was determined in 45 patients with hyperthyroidism due to Graves' disease who had been diagnosed and treated with thionamide drugs between 1965 and 1971 and had remained clinically euthyroid for greater than 10 yr after discontinuation of therapy. Physical examination revealed that only 2 patients had signs of mild hyperthyroidism; all others were euthyroid. Measurements of serum concentrations of thyroid hormones and TSH revealed elevated free T4 index values and serum T3 in 3 (6.7%), T3 toxicosis in 4 (8.9%), and subclinical hypothyroidism in 2 patients (4.4%). The remaining 36 patients were biochemically euthyroid. TRH tests were performed in these 36 patients, and hyporesponsiveness was found in 3 and hyperresponsiveness in 5 patients. T3 suppression tests were performed in 15 of the 36 patients; 10 were suppressible and 5 were nonsuppressible. All suppressible patients responded to TRH. Large needle biopsies performed in 8 biochemically euthyroid patients and 1 patient with subclinical hypothyroidism revealed chronic lymphocytic thyroiditis in 7 and normal biopsies in 2 patients. Diffuse epithelial hyperplasia was not found in any of the specimens. Antithyroid antibody titers were significantly higher than in 1972 at the time of discontinuation of therapy using the same methods. These results suggest that Graves' disease may evolve into chronic thyroiditis in some patients who are in permanent remission, and some patients in apparent permanent remission have hyperthyroidism and concomitant chronic thyroiditis.

Thyroid-stimulating antibody bioassay using porcine thyroid cells cultured in follicles.

Isolated porcine thyroid cells were cultured in agarose-coated dishes and allowed to reform follicles with normal polarity. The thyroid cells reaggregated into follicles were compared with cells cultured in monolayer for cAMP responsiveness to TSH and thyroid-stimulating antibody (TSAb). The cells in follicles were sensitive to TSH stimulation and responded to the hormone at concentrations as low as 3.3-10 microU/ml with an increase in cAMP production. In contrast, 10-50 microU/ml TSH were required to elicit a cAMP response in cells cultured in monolayer using identical conditions. cAMP responsiveness to TSAb also was greater in the cells organized into follicles. TSAb was detected in serum from 89.4% of 66 untreated patients with hyperthyroid Graves' disease using thyroid follicles, but TSAb was detected in serum from only 60% of the patients when assayed using cells in monolayer. The assay using thyroid follicles was used to measure TSAb in 27 euthyroid patients who were euthyroid while receiving thionamide therapy and compared with 20-min thyroid 131I uptake after T3 suppression. TSAb was present in 11 of 12 nonsuppressible patients and in 5 of 15 suppressible patients. TSAb was positively correlated with 20-min 131I thyroid uptake. We conclude that thyroid cells cultured in follicles are suitable for measuring TSAb.

How to deal with undetectable and low measurable serum thyroglobulin levels in the follow-up of patients with differentiated thyroid carcinoma?

Serum thyroglobulin (Tg) was measured in 52 patients 3 months to 15 years (mean 5.3 years) after thyroidectomy with or without subsequent radioablation for differentiated thyroid carcinoma, before and after the interruption of suppressive thyroxine (T4) replacement therapy for 5 weeks. Whole body scintigraphy was carried out at the end of the T4 withdrawal period. Serum Tg was undetectable (less than 3 micrograms/l) in 38 patients on T4 therapy, in 18 the scintigraphy showed a minimal accumulation in the neck region and in 20 no uptake anywhere after withdrawal of T4. In the former group Tg rose in 10 patients to 4-21 micrograms/l when off T4 which seemed to correspond to the normal tissue left in situ, in the latter group Tg rose only in 2 patients to 5 and 21 micrograms/l, respectively. Two patients out of 14 with detectable Tg on T4 had pulmonary metastases as uncovered by whole body scintigraphy (in one of them Tg rose from 12 micrograms/l on T4 to 1200 micrograms/l off T4) and 6 patients were suspected for having recidual cancer tissue (2 patients had a negative scintigraphy) because the Tg rose (66-215 micrograms/l) over the upper limit of the reference range (less than 50 micrograms/l) after T4 withdrawal. In conclusion, in the follow-up of patients with differentiated thyroid carcinoma no routine scans are needed as long as serum Tg remains undetectable but further examinations are shortly warranted when detectable Tg is obtained during T4 suppression.

Serum thyroid hormone changes during whole body hyperthermia.

In order to elucidate changes in thyroid hormone metabolism during acute heat stress, we measured sequentially serum thyroxine (T4), triiothyronine (T3), and reverse T3 (rT3) levels in 5 patients with neoplasia during treatment with whole body hyperthermia. The core temperature was raised from 37.0 degrees C to 42.0 degrees C over a 2-hour period, maintained at 42.0 degrees C for 2 hours, and then cooled to 37.0 degrees C over 2 hours. This short period of severe hyperthermia produced a fivefold rise in rT3 and a fall in T3 levels to one half of baseline levels. T4 and free T4 levels increased slightly, but thyrotropin (measured in two patients) did not change. These changes in T3 and rT3 levels were detectable at the fourth hour after onset of hyperthermia, were maximal at 24 and 48 hours, and in one patient were uncorrected after 4 days. We conclude that this reciprocal change in T3 and rT3 levels is a response to stress and may represent in part adaptation to a high environmental temperature by the suppression of theromengic T3. Whole body hyperthermia of short duration for cancer therapy produces profound changes in the peripheral degradation of thyroxine, which last for several days. This must be considered in the management of patients receiving hyperthermia, and the technique itself may prove to be a useful model for the study of adaptation to heat stress.

The differential diagnostic problems in unilateral euthyroid Graves' ophthalmopathy.

Nine consecutive patients with unilateral ophthalmopathy with suspected endocrine pathogenesis were investigated with a TRH test, a T3 suppression-test, thyroid autoantibodies and a subsequent computerized tomography (CT)-scan. All patients were clinically and biochemically euthyroid. Seven of 9 patients had a normal TRH test and 6 of 7 had a normal T3 suppression test. Slightly to moderately elevated microsomal and thyroglobulin (determined with radioimmunoassay) autoantibodies were found in 5 of 8 patients and in 1 patient thyroid stimulating immunoglobulins (TSI) were found. Three of the patients had normal thyroid function tests and no detectable thyroid autoantibodies. The subsequent CT-scan revealed that one of these had a maxillary tumour protruding into the orbita. The remaining 8 patients had enlargement of one (3 patients) or more (5 patients) eye muscles. Two of the 8 patients had bilaterally enlarged eye muscles, one of which was the patient with positive TSI. The remaining 6 patients had unilateral extraocular muscle enlargement. Thus, 2 of 9 patients had ophthalmopathy without thyroid dysfunction so-called isolated autoimmune ophthalmopathy or Graves' ophthalmopathy. Thyroid function tests seem to be of limited value in the diagnosis between endocrine and non-endocrine eye disease, and we recommend the use of diagnostic imaging (e.g. CT-scan) in patients with unilateral exophthalmus in order to diagnose malignant processes.

Serum thyroglobulin levels as a good indicator of t3 suppressibility

Serum thyroglobulin levels as a good indicator of t3 suppressibility

Reappraisal of the 3,5,3'-triiodothyronine-suppression test in the prediction of long term outcome of antithyroid drug therapy in patients with hyperthyroid Graves' disease.

Thyroidal suppressibility by exogenous T3 in terms of both radioiodine uptake (RAIU) and serum T4 was evaluated in 115 hyperthyroid patients treated with methimazole for 2 yr and followed for an additional 2 yr to study the rate of recurrence. Various other serum parameters including serum thyroglobulin concentrations, thyroid autoantibody, and TSH receptor antibody titers, and thyroidal responses to TRH-induced TSH elevation were also determined. After 2 yr of methimazole therapy, thyroidal RAIU was not suppressible (RAIU less than 12%/4 h was defined as suppressible) in 50 of 115 patients (group I). Of 65 patients with suppressible thyroid RAIU, serum T4 was significantly reduced (less than 60% of pre-T3 level) by T3 administration in only 43 patients (group III) but not in the remainder (group II). Antithyroid drug therapy was discontinued in the group II and III patients, and 7 of the patients had recurrence of hyperthyroidism within 2 yr of follow-up. All of them were from group II. The thyroidal response to TSH was greater in group III patients than in group II patients. During antithyroid drug therapy, decrease of microsomal antibody titer was more likely to occur in group III patients than in those of group II. Serum thyroglobulin concentrations were uniformly normal in treated patients irrespective of T3 suppressibility. TSH receptor antibody was positive in all 13 untreated patients with Graves' disease but was negative in treated patients regardless of their T3 suppressibility. Measurement of both thyroidal RAIU and serum T4 after administration of T3 improves the reliability of T3-suppression testing as a predictor of the remission of Graves' disease.

Acute posttranscriptional regulation of cerebrocortical and pituitary iodothyronine 5'-deiodinases by thyroid hormone.

Cerebrocortical and pituitary iodothyronine 5'-deiodinases produce 50% or more of the T3 found in these tissues and show rapid 3- to 5-fold changes in response to changes in the thyroid status. Since many T3 responses are initiated in the cell nucleus and require protein synthesis, we studied the influence of cycloheximide and actinomycin D on the acute T3 suppression of cerebrocortical and pituitary 5'-deiodinase activities in hypothyroid rats. Cycloheximide inhibited protein synthesis by more than 95%, but did not prevent the rapid (4-h) T3-mediated decreases in 5'-deiodinase activity. In the presence of cycloheximide, T3 decreased enzyme activity by more than 85%, with a t1/2 of approximately 70 min in the cerebral cortex and about 110 min in the pituitary. In vitro, neither T3 nor cycloheximide in large excess had any effect on enzyme activity. In cycloheximide-treated rats, cerebrocortical 5'-deiodinase activity decreased with a fractional turnover rate (k) of 1.2 h-1 in euthyroid and 0.07 h-1 in hypothyroid rats, respectively, with corresponding steady state enzyme levels of 18 +/- 3 and 145 +/- 9 U/mg protein. The resulting production rates of cerebrocortical 5'-deiodinase were 22 and 10 U/mg protein X h. Actinomycin D failed to alter either the cerebrocortical 5'-deiodinase in euthyroid rats in 4 h or the inhibitory effect of T3, but inhibited RNA synthesis by more than 70%. These data indicate that the T3-dependent fall in cerebrocortical 5'-deiodinase is mediated by a posttranscriptional mechanism that ultimately increases the rate of degradation/inactivation of the enzyme.

Goiter in Children

The diagnostic evaluation of the patient with thyromegaly will be determined by the clinical history and an examination of the thyroid gland (Table 9). In most instances the diagnosis will not be in doubt, and only a few tests will be necessary. For example, the euthyroid adolescent female with an asymmetrically or symmetrically enlarged, firm thyroid gland has a presumptive diagnosis of CLT, and only tests of thyroid function (T4 and TSH) and thyroid antibodies may be needed for confirmation. Similarly, the patient with clinical symptoms and signs of hyperthyroidism, exophthalmus, and a diffusely enlarged, soft thyroid gland has a presumptive diagnosis of Graves disease. The necessary tests include only a measurement of T4, an estimate of free T4, and WBC and differential counts prior to the initiation of antithyroid drug therapy. [See table in the PDF file] In the absence of an obvious diagnosis, the clinician will select the specific diagnostic tests depending upon the examination of the thyroid gland. The cause of smooth, symmetrical, diffuse enlargement of the thyroid gland can be suspected with careful history for familial disease, history of exposure to goitrogens and goitrogenic drugs, and the determination of thyroid antibodies in serum. If the clinical history is suggestive of hyperthyroidism, the tests of thyroid function tests should include determination of serum T3 concentration; if the history is compatible with euthyroidism or hypothyroidism, thyroid function tests should include determination of serum TSH concentration for the presence of compensated primary hypothyroidism. If results of these tests are normal, no additional tests are necessary, and the patient should be reassured and seen again in six months. If the patient has a test that is negative for thyroid antibodies and an elevation of serum TSH concentration, a radioactive [123I]iodide uptake and perchlorate discharge test will be helpful in the diagnosis of familial dyshormonogenesis. The patient with constitutional symptoms of inflammatory disease, history of a recent upper tract respiratory infection, and a tender or nontender enlarged thyroid gland may have subacute thyroiditis; a low or absent uptake of radioiodine with high-normal or elevated T4 and T3 concentrations will be suggestive of that diagnosis. In patients with thyromegaly and mild symptoms of hyperthyroidism, a TRH test will help to discriminate hyperthyroxinemia secondary to increased or abnormal serum thyroxine binding proteins from early Graves disease, factitious hyperthyroidism, toxic thyroiditis, and TSH-mediated hyperthyroidism. The T3 suppression test is a definitive diagnostic test for early, mild Graves disease. The euthyroid patient with mild-to-moderate thyromegaly and tests that are negative for thyroid antibodies usually deserves no further diagnostic evaluation, but should be followed with a presumptive diagnosis of idiopathic goiter or mild CLT. On follow-up evaluation, initially at six-month intervals and subsequently at yearly intervals, the patient should have a clinical and biochemical assessment until thyromegaly regresses and the gland is normal in size and consistency. The patient with a nontender, firm, irregular enlargement of the thyroid gland usually has CLT. If results of thyroid function tests are normal and tests for thyroid antibodies are negative, the patient should be seen again in four to six months and serum thyroid antibody determinations again performed. Another test that may give abnormal results in patients with CLT is the perchlorate discharge test. The approach to the patient with the solitary thyroid nodule differs from that of the previously described clinical presentations. The most important studies for the patient with a thyroid nodule are those designed to determine the structure and consistency of the thyroid gland, namely, ultrasonography to distinguish between solid and cystic lesions, and the radionuclide scan to determine whether the nodule is functioning (hot) or nonfunctioning (cold). To assure that the thyroid nodule is not associated with a nonsurgical lesion such as Hashimoto thyroiditis, serum thyroid antibody determinations are important. As malignancy of the thyroid gland is usually not associated with abnormalities of thyroid function, it is important to perform laboratory tests to exclude hyperthyroidism (a serum T3 determination) and hypothyroidism (a serum TSH determination) at the time of initial evaluation. Additional tests are usually not necessary unless the patient had mild hyperthyroidism with an autonomously functioning nodule, in which case the T3 suppression test and TRH test are often useful; rarely, the TSH stimulation test is helpful in determing whether thyroid tissue throughout the remainder of the gland is suppressed. A solitary, solid, nonfunctioning (cold) nodule requires excisional biopsy.

Goiter in Children

The diagnostic evaluation of the patient with thyromegaly will be determined by the clinical history and an examination of the thyroid gland (Table 9). In most instances the diagnosis will not be in doubt, and only a few tests will be necessary. For example, the euthyroid adolescent female with an asymmetrically or symmetrically enlarged, firm thyroid gland has a presumptive diagnosis of CLT, and only tests of thyroid function (T4 and TSH) and thyroid antibodies may be needed for confirmation. Similarly, the patient with clinical symptoms and signs of hyperthyroidism, exophthalmus, and a diffusely enlarged, soft thyroid gland has a presumptive diagnosis of Graves disease. The necessary tests include only a measurement of T4, an estimate of free T4, and WBC and differential counts prior to the initiation of antithyroid drug therapy. [See table in the PDF file] In the absence of an obvious diagnosis, the clinician will select the specific diagnostic tests depending upon the examination of the thyroid gland. The cause of smooth, symmetrical, diffuse enlargement of the thyroid gland can be suspected with careful history for familial disease, history of exposure to goitrogens and goitrogenic drugs, and the determination of thyroid antibodies in serum. If the clinical history is suggestive of hyperthyroidism, the tests of thyroid function tests should include determination of serum T3 concentration; if the history is compatible with euthyroidism or hypothyroidism, thyroid function tests should include determination of serum TSH concentration for the presence of compensated primary hypothyroidism. If results of these tests are normal, no additional tests are necessary, and the patient should be reassured and seen again in six months. If the patient has a test that is negative for thyroid antibodies and an elevation of serum TSH concentration, a radioactive [123I]iodide uptake and perchlorate discharge test will be helpful in the diagnosis of familial dyshormonogenesis. The patient with constitutional symptoms of inflammatory disease, history of a recent upper tract respiratory infection, and a tender or nontender enlarged thyroid gland may have subacute thyroiditis; a low or absent uptake of radioiodine with high-normal or elevated T4 and T3 concentrations will be suggestive of that diagnosis. In patients with thyromegaly and mild symptoms of hyperthyroidism, a TRH test will help to discriminate hyperthyroxinemia secondary to increased or abnormal serum thyroxine binding proteins from early Graves disease, factitious hyperthyroidism, toxic thyroiditis, and TSH-mediated hyperthyroidism. The T3 suppression test is a definitive diagnostic test for early, mild Graves disease. The euthyroid patient with mild-to-moderate thyromegaly and tests that are negative for thyroid antibodies usually deserves no further diagnostic evaluation, but should be followed with a presumptive diagnosis of idiopathic goiter or mild CLT. On follow-up evaluation, initially at six-month intervals and subsequently at yearly intervals, the patient should have a clinical and biochemical assessment until thyromegaly regresses and the gland is normal in size and consistency. The patient with a nontender, firm, irregular enlargement of the thyroid gland usually has CLT. If results of thyroid function tests are normal and tests for thyroid antibodies are negative, the patient should be seen again in four to six months and serum thyroid antibody determinations again performed. Another test that may give abnormal results in patients with CLT is the perchlorate discharge test. The approach to the patient with the solitary thyroid nodule differs from that of the previously described clinical presentations. The most important studies for the patient with a thyroid nodule are those designed to determine the structure and consistency of the thyroid gland, namely, ultrasonography to distinguish between solid and cystic lesions, and the radionuclide scan to determine whether the nodule is functioning (hot) or nonfunctioning (cold). To assure that the thyroid nodule is not associated with a nonsurgical lesion such as Hashimoto thyroiditis, serum thyroid antibody determinations are important. As malignancy of the thyroid gland is usually not associated with abnormalities of thyroid function, it is important to perform laboratory tests to exclude hyperthyroidism (a serum T3 determination) and hypothyroidism (a serum TSH determination) at the time of initial evaluation. Additional tests are usually not necessary unless the patient had mild hyperthyroidism with an autonomously functioning nodule, in which case the T3 suppression test and TRH test are often useful; rarely, the TSH stimulation test is helpful in determing whether thyroid tissue throughout the remainder of the gland is suppressed. A solitary, solid, nonfunctioning (cold) nodule requires excisional biopsy.

Natural and synthetic analogues of melatonin and related compounds. II. Effects on plasma thyroid hormones and cholesterol levels in male Syrian hamsters.

Synthetic or natural analogues of the pineal indole, melatonin, were injected separately every evening (1700 hours) for 7 (Exp. 1) or 10 (Exp. 2) weeks into adult male Syrian hamsters maintained in 14 hours of light and 10 hours of darkness each day. Plasma thyroxine (T4) levels were significantly depressed by 25 micrograms/day of melatonin (aMT) in both experiments. Injecting 25 micrograms/day either of acetyl methoxytryptophol or of synthetic analogues (hexanoyl methoxytryptamine, propionyl methoxytryptophol, or 6-chloro-melatonin) in Exp. 1 or of a natural analogue (N-acetylserotonin, 6-hydroxy-melatonin, hydroxytryptophol, or methoxytryptophol) in Exp. 2 had no effect on the circulating T4 levels. Plasma levels of triiodothyronine (T3) and thyrotropin (TSH) were unaffected in either experiment. Since none of the tested melatonin analogues is capable of suppressing circulating T4 concentration when given in a dose at which melatonin is reproducibly effective, the pineal-induced suppression of T4 is most likely mediated by melatonin. Plasma cholesterol levels were elevated only in hamsters receiving 6-chloromelatonin injections. However, plasma triglyceride levels were significantly higher than the diluent treated controls in Exp. 1 after injections of melatonin, acetyl methoxytryptophol, propionyl methoxytryptophol and 6-chloromelatonin. Interscapular brown adipose tissue was significantly heavier in melatonin treated animals.

Outcome of patients with Graves' disease after long-term medical treatment guided by triiodothyronine (T3) suppression test.

The value of the T3 suppressed 20-min uptake test for the prediction of post-treatment outcome was studied in 193 unselected patients with Graves' disease treated with thionamide drugs and T3. One hundred and twenty-nine of 193 patients were studied previously and followed thereafter (Group A). Sixty-four were newly treated patients: thirty-three (Group B) were treated at the same hospital as Group A; thirty-one (Group C) were treated at another hospital. In total 126 patients out of 193 satisfied our criteria for suppression (total suppression rate, 65%). The suppression rate for new patients (55% in Group B, 52% in Group C) was similar to that for Group A in 1977 (49%) after comparable duration of treatment. The suppression rate for Group A increased with prolongation of the treatment period (49% in 1977 and 71% in 1981). As to the time course of suppression, it was observed that about two-thirds of the suppressed patients satisfied the criteria for suppression within 3 years of starting treatment. The number of suppressed patients per year decreased thereafter as the treatment periods increased. However, the yearly suppression rate did not decrease with time. The time course of suppression in each patient could not be predicted from the results of initial thyroid function tests. The overall remission rate among the 120 suppressed patients followed for 1-13 (mean, 4) years was 96%, which was almost equal to the value obtained in Group A in 1977 (95%) with the average follow-up period of 2 years. Among the 46 patients in Group A followed for 5-13 (mean, 7) years, no increase in relapse was observed with prolonged follow-up periods. Examination on the relationship between the duration of treatment and the post-treatment outcome revealed that, as a whole, the duration of treatment for the patients with relapse were rather short as compared with those for the patients in remission. These results confirm the usefulness of our T3 suppression test for predicting sustained remission of Graves' disease after treatment, and clearly indicate that long-term medical therapy could increase the number of remissions in patients with Graves' disease.

Critical role played by thyroid hormone in induction of neoplastic transformation by chemical carcinogens in tissue culture.

Incubation of primary cultures of hamster embryo cells (HEC) or mouse fibroblasts (C3H/10T1/2 cells) in media depleted of thyroid hormones does not alter cell growth or survival but renders the cells resistant to neoplastic transformation by benzo[a]pyrene (B[a]P) or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), carcinogens which yield transformation rates of 10(-4)-10(-2) in media supplemented with triiodothyronine (T3). In C3H/10T1/2 cells, the times of addition or removal of the hormone indicate that T3 exerts maximum effect when added 12 hr prior to treatment with B[a]P and that the progression of transformation from the time of initiation by the carcinogen to full expression and the appearance of transformed foci was independent of the presence or absence of the hormone in the medium. Dependence of transformation on T3 concentration in the medium was observed over the physiological range of 1 pM to 100 nM in C3H/10T1/2 cells treated with B[a]P. These results were similar to our previous findings on the T3 dose-related induction of radiogenic transformation and of Na+,K+-ATPase activity. The latter effect was used as a measure of T3 induction of protein synthesis. A further indication of the potential involvement of protein synthesis in T3 action is the suppression of T3- and B[a]P-dependent transformation by cycloheximide at concentrations that inhibit protein synthesis by approximately equal to 50% in the C3H/10T1/2 cells. We suggest that thyroid hormone induces the synthesis of a host protein that plays a key role in neoplastic transformation by direct-acting chemical carcinogens and by those requiring metabolic activation. In our previous studies, similar T3-dependent mechanisms were implicated in radiogenic transformations.

A study of thyroid function after subtotal thyroidectomy for Graves' disease: particularly on TRH tests, T3 suppression tests and antithyroid antibodies in euthyroid patients.

Of 305 patients who underwent subtotal thyroidectomy for Graves' disease between 1969 and 1975, recurrent hyperthyroidism was found in 31 (10.2%) and hypothyroidism in 18 (5.9%). The remaining 256 patients were clinically euthyroid, but an elevated serum TSH level was found in 104 (34.1%) and an elevated serum T3 level in 19 (6.28%). In 57 of 133 clinically and biochemically euthyroid patients, a TRH test, T3 suppression test and measurement of antithyroid antibodies were performed. Twenty-nine of the 57 patients (50.9%) showed an abnormal response to TRH. Eight of these (14.0%) showed an impaired or absent response. The T3 suppression test showed that 15 of the 57 patients (26.3%) were non-suppressible. Positive antithyroid antibodies, especially antimicrosomal antibodies, were more frequent in non-suppressible and TRH-non-responsive patients than in suppressible and TRH-responsive patients. It is suggested that after operation for Graves' disease: 1) only half of the clinically euthyroid patients were biochemically euthyroid, 2) of the clinically and biochemically euthyroid patients, there were many with abnormalities in TRH responsiveness and T3 suppressibility, and 3) thyroid functional status is unstable and long careful follow-up is important after operation for Graves' disease.

Responses to TRH, T3 suppression tests and histological findings by needle biopsy in patients with simple goitre in Japan.

Studies were performed in 120 patients with simple goitre, defined as relatively soft diffuse goitre. All were clinically and biochemically euthyroid and their antithyroid antibodies were negative. The TRH test was performed in 99 after the TRH test, while satisfactory biopsies of the thyroid were obtained in 37. The results showed that 28 of the 115 cases (24%) had an abnormal response to TRH; 8 (7%) were hyporesponders and 20 (17%) were hyperresponders. The T3 suppression test showed that 3 of 99 cases (3%) were non-suppressible. As determined by histological examination of the needle biopsy specimen, 17 of the 37 cases (46%) had normal follicles without lymphocytic infiltration, 10 (27%) had diffuse chronic thyroiditis, 5 (14%) had focal thyroiditis and 4 (11%) had diffuse epithelial hyperplastic change, and 1 (3%) had an adenomatous goitre. It is suggested that simple goitre defined as above includes various thyroid diseases and that the results of TRH tests, antithyroid antibody estimations and histological findings do not correlate in many patients.

Regulation of thyrotropin-releasing hormone receptors and responses by L-triiodothyronine in dispersed rat pituitary cell cultures.

The effects of physiological concentrations of L-T3 (T3) were examined in dispersed cell cultures of pituitaries obtained from 10- to 12-day-old rats. T3 inhibited TSH secretion by 50% and blunted the TSH response to TRH. The PRL response to TRH was also inhibited by T3, and GH secretion was increased 2-fold. These responses were half-maximal at 0.1 nM added T3 in medium supplemented with 10% hypothyroid calf serum, corresponding to a free T3 concentration of 5 pM. In the presence or absence of added T3, TRH effects were half-maximal at 0.5-3 nM, and T3 suppression was not overcome by high concentrations of TRH (up to 1 microM). Maximal inhibition of TSH responses to TRH occurred when cultures were preincubated with thyroid hormone for 24 h; a significant effect was observed after 8 h. The specific binding of [3H]TRH to dispersed rat pituitary cells was decreased 55-70% by T3 in a dose-dependent manner. Inhibition of TSH secretion by T3 was reversible within 24 h, and the fraction of thyrotrophs in the cultures (0.22) was not altered by T3 over the course of the experiments. The results demonstrate that physiological concentrations of T3 regulate TSH and PRL responses to TRH and control TRH receptor levels by a direct action on normal rat pituitary cells.

The prognosis of Graves' disease after antithyroid drug treatment: clinical significance of the T3 suppression test and abnormal thyroid stimulators

The prognostic significance of both the triiodothyronine (T3) suppression test and the detectability of thyroid stimulating immunoglobulins in patients with Graves' disease who had been treated with antithyroid drugs was evaluated. Eighty-three patients underwent a T3 suppression test after having been euthyroid for at least 6 months. In 33 patients, the human thyroid stimulator (HTS) was assayed by measuring cyclic AMP increase in cultured thyroid adenoma cells, and TSH-binding inhibitor immunoglobulins (TBII) were measured by using the radioreceptor assay of TSH. Among 43 patients who had discontinued the drug treatment, 37 patients were under observation for 6-42 months. When a fall in 30-minute thyroid 99mTcO4- uptake of 50% or more after T3 administration was defined as positive suppression, the relapse rate was 30% in non-suppressive cases and 26% in suppressive cases. The relapse rate was lower in cases whose pre-suppression uptake was less than 3.0% (3 out of 17 patients) or in cases whose uptake after T3 administration was less than 0.8% (1 out of 9 patients). Of 15 patients with negative suppression, 5 (33.3%) were positive in HTS and 4 (26.7%) were positive in TBII. On the other hand, two (11.1%) each of 18 patients with positive suppression were positive in HTS and TBII respectively. Neither HTS nor TBII had been detected at the cessation of therapy in any of the 12 patients who remained euthyroid during the follow-up period. On the other hand, four (44.4%) out of 9 patients who relapsed had been positive in either HTS of TBII. Thus the Graves' disease specific immunoglobulins were found to be significantly associated with the relapse of the disease (p less than 0.05). The above data indicates that regardless of the suppressibility of 99mTcO4- uptake after T3 administration, the rate of recurrence is high when the uptake after T3 is more than 0.9% and/or when either HTS or TBII are positive.

Pituitary-thyroid feedback regulation in patients with Graves' disease during antithyroid drug therapy.

In an attempt to study the mode of normalization of thyroid function in patients with Graves' disease, a study was made on 140 patients with Graves' disease who were eumetabolic after appropriate therapy with antithyroid drugs for more than 9 months. T3 administration failed to suppress thyroidal radioiodine uptake and serum T4 in patients with TRH-unresponsive TSH secretion. In addition, exogenous TSH failed to elevate serum levels of T4 and T3. In patients with TRH-responsive pituitaries, T3 administration uniformly made serum TSH undetectable but produced various effects (unsuppressible, partially suppressible, and suppressible) on radioiodine uptake and serum T4. The magnitude of suppression of radioiodine uptake paralleled that of serum T4. In patients with unsuppressible or partially suppressible thyroids, exogenous and endogenous TSH were less effective in elevating serum T4 and T3. In patients with suppressible thyroids, T3 administration depressed radioiodine uptake and serum T4; the magnitudes of depression were comparable to those found in normal subjects. Exogenous and endogenous TSH elevated serum T4 and T3 in patients with suppressible thyroids. Here again, the magnitudes of elevation were comparable to those found in the normal subjects. The serum T3 to T4 ratio was high before treatment, but decreased significantly during antithyroid drug therapy. The magnitude of decrease was roughly proportional to the degree of T3 suppressibility.