Peripheral resistance to thyroid hormone in an infant

Peripheral resistance to thyroid hormone, a syndrome characterized by elevated serum total and free thyroid hormone levels and abnormal TSH suppression without manifestations of hyperthyroidism, was studied in a clinically euthyroid 6-month-old infant. Initial serum concentrations of T4, T3, and TSH were 22.1 micrograms/dl, 334 ng/dl, and 7.6 microunits/ml, respectively; infusion of synthetic TRH increased the serum TSH to 47.4 microunits/ml, an exaggerated response. Pituitary insensitivity to T3 was investigated by measuring these parameters in response to consecutive 7-day courses of increasing doses of T3. Four times the calculated replacement dose of T3 (40 micrograms/day) was required to normalize the serum T4 and the serum TSH response to TRH. After administration of 80 micrograms/day T3, the serum TSH response to TRH was virtually abolished, but no clinical signs of thyroid hormone excess were observed. High doses of T4 blunted the serum TSH response to TRH in a manner similar to T3. Prednisone also decreased the TSH response to TRH but had no effect on serum thyroid hormone concentrations. In an attempt to determine the mechanism of thyroid hormone resistance, specific nuclear T3 binding was compared in cultured skin fibroblasts from the patient and a normal infant. Normal fibroblast nuclei had a single binding site with a Ka of 3.1 X 10(9) M-1. In contrast, the Scatchard plot of the patient's T3 binding was curvilinear, compatible with a high affinity site that had a Ka (4.2 X 10(9) M-1) similar to that of the normal fibroblasts and a second low affinity site (Ka = 2.7 X 10(8) M-1). Supraphysiological concentrations of T3 elicited a dose-related increase in fibroblast glucose consumption, which was similar in cells from both the patient and from a normal infant. In conclusion, pituitary and peripheral resistance to thyroid hormone has been demonstrated in this infant, but despite the abnormality of nuclear T3 binding, the cellular mechanisms remain unclear.     

RAPID ADAPTATION OF PITUITARY RESPONSIVENESS TO TRH IN THE POST-SURGICAL STATE. THE ROLE OF FREE T3

In eight clinically and biochemically euthyroid patients undergoing routine major non-thyroidal surgery preoperative and daily postoperative serum concentrations of total and free thyroid hormones were measured. Thyrotro-phin-releasing hormone (TRH) tests were performed preoperatively and on the first 3 postoperative days. There was a significant fall in mean serum total and free triiodothyronine (T3) concentrations on the postoperative days and mean reverse T3 concentrations rose reciprocally. There was no significant change in mean basal thyroid-stimulating hormone (TSH) values, but there was a significant increase in the mean TSH response to TRH on the first postoperative day. The mean TSH response then declined sequentially until day 3 while mean free T3 concentrations remained significantly depressed. Mean serum free thyroxine (T4) concentrations remained normal during the study. Intrapituitary conversion of T4 to T3 or other down regulatory mechanisms could explain this rapid adaptation of the pituitary axis.     

THYROID FUNCTION AND THYROID REGULATION IN EUTHYROID MEN WITH CHRONIC LIVER DISEASE: EVIDENCE OF MULTIPLE ABNORMALITIES

Total and free serum thyroxine (T4) and triiodothyronine (T3), basal serum thyrotrophin (TSH) and the serum TSH response to a standard intravenous dose of thyrotrophin releasing hormone (TRH) have been measured in fifteen men with liver cirrhosis and in eight alcoholic men with fatty liver change. All the patients studied were clinically euthyroid. In cirrhotics, total T4 and free T4 (FT4) concentrations were normal as were free T3 (FT3) concentrations but total T3 concentrations were significantly reduced and basal TSH concentrations were significantly higher than normal. Alcoholics with fatty liver change had normal basal TSH concentrations and normal total and free thyroid hormone concentrations apart from reduced FT4. Correlation of thyroid function tests with liver function (serum albumin concentration) showed significant positive correlations for serum albumin with both total T3 and FT3 and significant negative correlations with both FT4 and basal TSH. Nine of fifteen cirrhotics had an abnormal serum TSH response to TRH, the commonest abnormal pattern being a delayed response (seven patients). Three of eight alcoholics with fatty liver change also had an abnormal TSH response to TRH. These findings not only show complex disturbances in hypothalamic-pituitary-thyroid relationships in chronic liver disease but also provide indirect evidence of reduced extra-thyroidal conversion of T4 to T3.     

Serum thyrotropin and prolactin in the syndrome of generalized resistance to thyroid hormone: responses to thyrotropin-releasing hormone stimulation and short term triiodothyronine suppression

Serum TSH and PRL levels and their response to TRH were measured in 11 patients with generalized resistance to thyroid hormone (GRTH), 6 euthyroid subjects, and 6 patients with primary hypothyroidism. TSH and PRL levels and their response to TRH were also measured after the consecutive administration of 50, 100, and 200 micrograms T3 daily, each for a period of 3 days. Using a sensitive TSH assay, all GRTH patients had TSH values that were elevated or within the normal range. On the basis of a normal or elevated TSH level, GRTH patients were classified as GRTH-N1 TSH (5 patients) or GRTH-Hi TSH (6 patients), respectively. Only GRTH patients with previous thyroid ablative therapy had basal TSH values greater than 20 mU/L. TSH responses, in terms of percent increment above baseline, were appropriate for the basal TSH level in all subjects. No GRTH patient had an elevated basal PRL level. PRL responses to TRH were significantly increased only in the hypothyroid controls compared to values in all other groups. On 50 micrograms T3, 7 of 12 (58%) nonresistant (euthyroid and hypothyroid) and 1 of 11 (9%) resistant subjects had a greater than 75% suppression of the TSH response to TRH. On the same T3 dose, 2 of 12 (17%) nonresistant and 4 of 11 (36%) resistant subjects had a greater than 50% suppression of the PRL response to TRH. On 200 micrograms T3, all subjects, except for 1 with GRTH, had a greater than 75% suppression of the TSH response to TRH. On the same T3 dose, while 11 of 12 (92%) nonresistant subjects had a greater than 50% reduction of the PRL response to TRH, only 3 of 10 (30%) resistant patients showed this degree of suppression (P less than 0.005). Without previous ablative therapy, serum TSH in patients with GRTH is usually normal or mildly elevated. The TSH response to TRH is proportional to the basal TSH level and is suppressed by exogenous T3. However, on 200 micrograms T3 basal TSH was not detectable (less than 0.1 mU/L) in all euthyroid subjects, but it was measurable in three of four GRTH patients with normal TSH levels before T3 treatment. PRL levels in GRTH are normal even when TSH is elevated. The PRL response to TRH is not increased in GRTH. In all subjects, exogenous T3 suppresses the PRL response to TRH to a lesser degree than the TSH response, but this difference is much greater in patients with GRTH.     

Free thyroxine, free triiodothyronine, and thyrotropin concentrations in hypothyroid and thyroid carcinoma patients receiving thyroxine therapy

Free thyroxine (FT4) and free triiodothyronine (FT3) concentrations in serum were measured by direct equilibrium dialysis methods in patients receiving thyroxine replacement or suppression therapy. Four of 50 hypothyroid patients euthyroid on replacement therapy (mean thyroxine dose 120 micrograms/day) had supranormal FT4 concentrations, whereas the FT3 concentrations were normal in all. Forty-one of 56 operated thyroid carcinoma patients on suppressive therapy (mean thyroxine dose 214 micrograms/day) had raised FT4 concentrations, whereas the FT3 concentrations was elevated in only one patient. There was a large difference in mean FT4 values for hypothyroid and thyroid carcinoma patients (17.2 vs 29.5 pmol/l), whereas the difference in mean FT3 values was small (5.0 vs 6.1 pmol/l), suggesting a decreased peripheral conversion of T4 to T3 with increasing concentrations of FT4. Serum TSH concentrations, as determined by an immunoradiometric assay, varied from less than 0.02 to 11.9 mU/l in treated hypothyroid patients; 21 patients (42%) had values outside the reference limits. As a single test, serum TSH is therefore not very useful for the assessment of adequate thyroxine dosage in patients with primary hypothyroidism. In thyroid carcinoma patients, the TSH concentrations were less than 0.18 mU/l; 45 patients had values less than 0.02 mU/l indicating sufficient suppression of TSH secretion in the majority of cases. On the basis of these results we recommend the combination of FT3 and TSH tests for monitoring thyroxine replacement and suppression therapy. FT4 appears less useful than FT3 for this purpose even if special reference values values were adopted for each patient group.     

The comparative effect of T4 and T3 on the TSH response to TRH in young adult men.

The effect of graded increments of chronically administered oral T4 or T3 on the TSH response to TRH was studied in normal young adult men. The TSH response was assessed in the baseline state and after each increment of each hormone (two weeks at each dose level) using both 30 mug and 500 mug doses of TRH. Each thyroid hormone caused a dose-related decrease in the TSH response to TRH; thus the TSH response could be used as a bioassay for the biologic activity of the thyroid hormones in man. The dose of thyroid hormone that caused a 50% suppression of the TSH response, or the SD50, was not different with either 30 mug or 500 mug of TRH indicating that thyroid hormone suppression of the TSH response is not more easily detected with a small dose of TRH. The mean SD50 for T4 was 115 mug/day, for T3 stopped 2 h before testing the mean SD50 was 29 mug/day, and for T3 stopped 24 h before testing it was 45 mug/day. Using the average SD50 for the two T3 regimens (37 mug/day), the calculated relative potency indicates that oral T3 is 3.3 times as potent as oral T4, a value in reasonable agreement with the value previously estimated with a calorigenic end-point. The mean dose of T4 needed to decrease the TSH response to TRH to below the normal range (max delta TSH of 2 muU/ml) was 150 mug/day; this value is probably more appropriate than the SD50 in the treatment of patients with primary hypothyroidism or goiter and was about the same (160 mug/day) using a peak TSH after TRH of 3 muU/ml as an end-point. Estimation of the SD50 in each subject showed a 2- to 3-fold range with all regimens of thyroid hormones; similarly there was a 2-fold in the dose of T4 needed to suppress the TSH response to TRH to below the normal range. Further, the difference in the mean SD50 for the two T3 regimens indicates that a single daily dose of oral T3 does not exert a constant biologic effect throughout the day. Thus, because of individual variation and, in the case of T3, because of changing activity during the day a given dose of thyroid hormone may have a widely varying biologic effect. There was also a 3-fold range in the relative potency of T3 to T4 in the four subjects treated with both hormones. This suggests that the therapeutic administration of a fixed ratio fo T3 to T4 may have a variable effect from patient to patient. Finally, the serum T4 rose while the serum T3 did not at a dose of T4 that abolished the TSH response to TRH, indicating that circulating T4 is a determinant of TSH secretion in normal man.     

TRH test as an index of suppression compared with the thyroid radioiodine uptake in euthyroid goitrous patients treated with thyroxine.

To determine an index of adequate suppression of pituitary TSH secretion in euthyroid goitrous patients treated with sodium levothyroxine (T4), TSH responses to 500 micrograms TRH given iv were compared with thyroid 24-h radioiodine uptakes during therapy with T4 in 12 euthyroid goitrous patients. The patients received sequentially 100, 150, 200, 250, and 300 micrograms T4 with the doses increased at 4-6 week intervals. The mean dose of T4 that reduced the peak TSH response to TSH to the lower limit of normal (TSH = 5 microU/ml) was 130 micrograms; the mean T4 dose that suppressed the TSH response to one-half the lower limit of normal (TSH = 2.5 microU/ml) was 165 micrograms. The mean T4 dose that nearly obliterated the TSH response was 200 micrograms; this degree of suppression occurred with doses of 100-300 micrograms T4 in individual patients. Suppression of thyroid uptake correlated closely with suppression of the TSH response to TRH. The goiter diminished in size significantly in 6 of the 12 patients during the 6 months of observation adn did not enlarge in any patient. The data indicate that suppression of the TSH response to TRH is a convenient technique to assess the adequacy of suppressive therapy of goiter.     

Factors affecting suppression of endogenous thyrotropin secretion by thyroxine treatment: retrospective analysis in athyreotic and goitrous patients

Factors affecting TSH suppression by L-T4 administration were retrospectively evaluated in 452 patients: 180 who were athyreotic after total thyroidectomy and remnant radioiodine ablation for differentiated thyroid carcinoma and 272 with nontoxic diffuse or nodular goiter. All patients were considered clinically euthyroid. TSH secretion was assessed by iv TRH stimulation testing. The T4 dose associated with an undetectable basal serum TSH level and no increase in serum TSH after TRH administration (suppressive dose) averaged 2.7 +/- 0.4 (SD) micrograms/kg body weight (BW)/day in athyreotic patients and 2.1 +/- 0.3 micrograms/kg BW/day in goitrous patients (P less than 0.001). The 25th-75th percentile intervals were 2.5-2.9 micrograms/kg BW/day for athyreotic patients and 1.9-2.3 micrograms/kg BW/day for goitrous patients. The suppressive dose of T4 was dependent in both groups on patient age, younger patients needing higher doses than older patients. The duration of treatment also proved to be an important parameter, since in both groups the percentage of patients with suppressed TSH secretion increased if TRH testing was carried out after at least 6 months after the initiation of therapy. Serum total T4, total T3, free T3 (FT3), free T4 (FT4) index, and FT3 index values did not differ in the two groups and were significantly higher (P less than 0.001) than in normal subjects. Mean serum FT4 was significantly higher in athyreotic patients than in goitrous patients with suppressed TSH secretion. Among athyreotic patients with suppressed TSH secretion, 24% had elevated serum FT4 and FT3, and 47% had elevated serum FT4 alone. Of goitrous patients with suppressed TSH secretion, 20% had elevated serum FT4 and FT3, and 27% had elevated serum FT4 alone. On the other hand, 35% of athyreotic patients and 14% of goitrous patients whose TSH secretion was not suppressed had elevated serum FT4. Serum sex hormone-binding globulin concentrations were measured in 3 groups of goitrous women. Values above normal limits were found in 13/26 patients (50%) with high serum FT4 and FT3, in 4/30 patients (13%) with elevated serum FT4 alone, and in 1/25 patients (4%) with normal FT4 and FT3. In conclusion: TSH suppression requires daily doses of T4 between 2.5 and 2.9 micrograms/kg BW in athyreotic patients and between 1.9 and 2.3 micrograms/kg BW in goitrous patients, with appropriate adjustments in relation to the age of the patient; Assessment of the adequacy of treatment should not be carried out before 6 months after the institution of therapy.     

重组人生长激素治疗对生长激素缺乏症患者甲状腺功能的影响

为探讨生长激素治疗对甲状腺功能的影响及其机制，给１９例特发性生长激素缺乏症患者每日皮下注射重组人生长激素（ｒｈＧＨ）Ｇｅｎｏｔｒｏｐｉｎ０．１ＩＵ／ｋｇ体重，治疗１年，观察治疗前后甲状腺功能及血促甲状腺激素（ＴＳＨ）对静脉推注促甲状腺素释放激素（ＴＲＨ）的反应。经Ｇｅｎｏｔｒｏｐｉｎ治疗后，患者血清Ｔ４及ＦＴ４水平较治疗前明显下降（Ｐ＜０．０１）；治疗半年后，血清ＦＴ３水平亦较治疗前下降（Ｐ＜０．０５）；而血清Ｔ３、３，３′，５′－三碘甲状腺原氨酸及ＴＳＨ水平无明显变化（０．２＜Ｐ＜０．３）。治疗１年后，８例患者血清ＦＴ４水平降至正常范围以下，依此将患者分为治疗后甲状腺功能正常组及降低组，结果证实甲状腺功能降低组在治疗前或治疗后ＴＳＨ对ＴＲＨ兴奋的反应均较甲状腺功能正常组高（Ｐ＜０．０５）。血清ＴＳＨ对ＴＲＨ的反应增强提示患者治疗前就已有潜在的ＴＲＨ缺乏，后者可能是ｒｈＧＨ治疗过程中ＦＴ４及Ｔ４水平下降的潜在基础。因此在ｒｈＧＨ治疗过程中需监测特发性生长激素缺乏症患者的甲状腺功能，以及时给予替代治疗。     

EFFECTS OF LOW DOSE ORAL IODIDE SUPPLEMENTATION ON THYROID FUNCTION IN NORMAL MEN

Previous studies have demonstrated that short-term oral iodide administration, in doses ranging from 1500 micrograms to 250 mg/day, has an inhibitory effect on thyroid hormone secretion in normal men. As iodide intake in the USA may be as high as 800 micrograms/d, we investigated the effects of very low dose iodide supplementation on thyroid function. Thirty normal men aged 22-40 years were randomly assigned to receive 500, 1500, and 4500 micrograms iodide/day for 2 weeks. Blood was obtained on days 1 and 15 for measurement of serum T4, T3, T3-charcoal uptake, TSH, protein-bound iodide (PBI) and total iodide, and 24 h urine samples were collected on these days for measurement of urinary iodide excretion. TRH tests were performed before and at the end of the period of iodide administration. Serum inorganic iodide was calculated by subtracting the PBI from the serum total iodide. We found significant dose-related increases in serum total and inorganic iodide concentrations, as well as urinary iodide excretion. The mean serum T4 concentration and free T4 index values decreased significantly at the 1500 micrograms/day and 4500 micrograms/day doses. No changes in T3-charcoal uptake or serum T3 concentration occurred at any dose. Administration of 500 micrograms iodide/day resulted in a significant increase (P less than 0.005) in the serum TSH response to TRH, and the two larger iodide doses resulted in increases in both basal and TRH-stimulated serum TSH concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

SERUM THYROGLOBULIN IN PATIENTS WITH AUTONOMOUS THYROID NODULES

To investigate further the relationship between thyroid hormones and thyroglobulin (TG) secretion, total and free thyroid hormone levels, TSH and its response to TRH and serum TG concentrations were determined in 61 patients with solitary autonomous thyroid nodules. Thyroid function varied widely from euthyroidism to clearcut thyrotoxicosis. Serum TG levels were significantly higher in patients than in normal controls. Individually they were above the normal range (greater than 50 ng/ml) in 95% of the patients, as well as in those with normal total and/or free thyroid hormone levels. Patients with high total and/or free thyroid hormone levels had higher TG concentrations than euthyroid patients. TG concentrations were significantly correlated with FT3 values. They were higher in patients in whom TSH was unresponsive to TRH than in the responsive groups. TG was also slightly higher in patients with hot nodules than in those with warm nodules. These data seem to indicate that TG is secreted along with thyroid hormones in the absence of any stimulatory action. It also is a sensitive index of thyroid hyperfunction. Twenty patients were controlled 6 months after nodulectomy. TG levels, though significantly lower than in the preoperative state, were still higher than in normal subjects. This increase was attributed to persistent hyperthyroidism in two patients only. The observation that the increase in TSH after TRH stimulation in post-operative patients was greater than that found in normal controls led us to believe that in most cases the high TG levels after surgery are due to stimulation of the normal thyroid tissue by rebound TSH secretion.     

Serum free thyroxine in patients with T3-toxicosis

The serum free thyroxine concentration was measured by direct radioimmunoassay in 38 untreated T3-thyrotoxic patients with elevated serum total and free triiodothyronine, normal serum thyroxine and free thyroxine index, no TSH response to TRH, and with clinical evidence of hyperthyroidism. An elevation of circulating free thyroxine values was observed in 58% of the patients, whereas total serum thyroxine concentration was within the normal range. It is suggested, therefore, that T3-thyrotoxicosis should be reserved for patients with elevated serum total T3 and free T3 concentrations and normal serum total T4 and free T4 concentrations. Serum thyroxine-binding globulin concentrations were significantly lower (P less than 0.025) in patients with an elevated serum free thyroxine (18.7 +/- 3.6 micrograms/ml: mean +/- SD) as compared with those in patients with a normal free thyroxine concentration (23.4 +/- 2.6 micrograms/ml). In addition, no daily fluctuations in total and free thyroxine concentration were observed in 6 patients over a 4-8 day period.     

Alteration of thyroid function in the early stage of subacute thyroiditis

Measurement of serum triiodothyronine (T3), thyroxine (T4), free triiodothyronine (FT3), free thyroxine (FT4), thyroxine-binding-globulin (TGB), antithyroglobulin antibodies (anti-hTg), thyroid 131I uptake and scanning was performed on 12 patients during the early phase of subacute thyroiditis. Serum thyrotropin (TSH) was measured during baseline conditions and following administration of synthetic thyrotropin-releasing-hormone (TRH). The stimulation with exogenous TSH was performed on 7 subjects. 131I uptake was depressed in all patients including those with solitary nodules. Free and total hormone concentrations were elevated in the three cases with diffuse gland involvement, whereas an increase of T3 alone was present in 3 patients with unilobar involvement. In the latter group and in the 2 patients with a nodular form T4, FT3 and FT4 levels were within normal limits. Interruption of the pituitary-thyroid feed-back mechanism with absence of thyrotropin response to TRH occurred in 11 patients, independent of whether thyroid hormone concentrations were elevated or normal. In one patient only with unilateral involvement, TSH responsiveness to TRH was normal while 131I uptake was not raised by exogenous TSH, indicating diffuse cellular damage. The normal values of FT3 and FT4 found in patients with normal T3 and T4 levels seem to exclude the possibility that the free hormones are responsible for the interrupted feed-back which represents the main cause of suppressed iodine uptake. However, it is possible that the pituitary-thyroid axis is responding to transient or light increases of free and total T3 and T4 still within their 'normal range'.     

TRIAC (3,5,3''-triiodothyroacetic acid) has parallel effects at the pituitary and peripheral tissue levels in thyroid cancer patients treated with l-thyroxine

OBJECTIVE: To investigate whether the addition of 3,5,3'-triiodothyroacetic acid (TRIAC) to thyroxine (T4) treatment can suppress TSH secretion without inducing thyrotoxicosis at the periphery. DESIGN: Thyroid cancer patients were studied with different treatment modalities: T4 at supraphysiologic dose (2.5 +/- 0.3 micrograms/kg/day) and after reduction to a physiologic dose (1.8 +/- 0.3 micrograms/kg/day); then with the addition of TRIAC 500 or 1000 micrograms/day to the physiologic T4 treatment dose. PATIENTS: Twenty-two patients who had total thyroid ablation for differentiated thyroid carcinoma. MEASUREMENTS: Clinical and biological parameters of thyroid hormone action studied included heart rate, serum creatine phosphokinase, testosterone-oestradiol binding globulin, procollagen III and osteocalcin levels. RESULTS: The addition of TRIAC induced a significant and dose-dependent decrease in serum TSH levels and parallel effects on peripheral tissues. Compared to the suppressive T4 treatment dose, the addition of TRIAC to the physiologic T4 dose resulted in greater inhibition of TSH secretion in only 50% of the patients. The effects at the periphery of both treatment modalities were similar for a comparable level of TSH suppression. CONCLUSIONS: Even at low dose and when combined with T4, TRIAC has parallel effects on the pituitary and peripheral tissues. There is no justification for the use of TRIAC as suppressive treatment in thyroid cancer patients.     

A case of cushing syndrome with both secondary hypothyroidism and hypercalcemia due to postoperative adrenal insufficiency

A 48-year-old woman was referred to our hospital because of secondary hypothyroidism. Upon admission a left adrenal tumor was also detected using computed tomography. Laboratory data and adrenal scintigraphy were compatible with Cushing syndrome due to the left adrenocortical adenoma, although she showed no response to the TRH stimulation test. Hypercortisolism resulting in secondary hypothyroidism was diagnosed. After a left adrenalectomy, hydrocortisone administration was begun and the dose was reduced gradually. After discharge on the 23rd postoperative day, she began to suffer from anorexia. ACTH level remained low, and serum cortisol, free thyroxine and TSH levels were within the normal range. Since her condition became worse, she was re-admitted on the 107th postoperative day at which time serum calcium level was high (15.6 mg/dl). Both ACTH response to the CRH stimulation test and TSH response to the TRH stimulation test were restored to almost normal levels, but there was no response of cortisol to CRH stimulation test. We diagnosed that the hypercalcemia was due to adrenal insufficiency. Although the serum calcium level decreased to normal after hydrocortisone was increased (35 mg/day), secondary hypothyroidism recurred. It was suggested that sufficient glucocorticoids suppressed TSH secretion mainly at the pituitary level, which resulted in secondary (corticogenic) hypothyroidism. However, both postoperative glucocorticoid deficiency and adequate amounts of thyroxine due to the elimination of inhibition of TSH secretion by glucocorticoids might cause hypercalcemia possibly through increased bone reabsorption of calcium.     

Response to thyrotropin releasing hormone: an objective criterion for the adequacy of thyrotropin suppression therapy.

Most serum thyrotropin (TSH) assays do not adequately discriminate between normal values and absent TSH. We therefore evaluated the TSH response to thyrotropin releasing hormone (TRH) as a criterion for the adequacy of TSH suppression therapy. Twenty-six outpatients with various thyroid disorders (cancer, 10; nodules, 9; miscellaneous, 4; hypothyroidism after 131I therapy for Graves' disease, 3) were studied. Using the frequent sampling technique (samples every 20 min) in two normal volunteers and one untreated patient who was TRH-responsive, we first confirmed the observation that TSH secretion occurred episodically throughout the 24-h period. In contrast, serum TSH was undetectable (less than 0.6 micronU/ml) throughout the 24-h period in 5 patients on TSH suppression therapy who were TRH-unresponsive and one who had a minimal response to TRH. Thus, TRH-unresponsive patients did not secrete measurable amounts of TSH throughout the 24-h period. To suppress TSH secretion, all patients were treated with L-thyroxine (T4) at doses which resulted in undetectable TSH values in random plasma samples. TRH tests were carried out only when random TSH concentrations were less than 0.6 micronU/ml. Seven of the twenty-six patients (27%) including two with thyroid cancer were TRH-responsive indicating a potential for TSH secretion. In these seven, the T4 dose was adjusted until they were TRH-unresponsive. The mean change in T4 dose of these 7 patients was 20+/-10 (SD) microng/day and this resulted in a mean increase of 1.5+/-1.1 microng/dl for T4 and 20+/-20 ng/dl for T3. For all patients, the mean T4 dose required for TSH suppression was 172+/-53 microng/day or 2.6+/-0.8 microng per day per kg body weight. Twenty-three of 26 patients required between 100-200 microng/day and the remaining 3, 250-300 microng/day. The T4 dose required to suppress TSH resulted in normal serum concentrations of T4. 9.1+/-2.0 MICRONG/DL, AND T3, 136.7+/-33.6 NG/DL. These T4 doses did not produce a rapid heart rate, either awake or asleep, arrhythmias, or electrocardiographic abnormalties as assessed by 24-h Holter monitor tracings in 11 patients. Our results thus show that the T4 dose which results in an unresponsive TRH test ensures that serum TSH will remain undetectable (less than 0.6 micronU/ml) throughout the 24-h period. An unresponsive TRH test, therefore, appears to be a very useful and reliable index of TSH suppression.     

Effect of clomifene on thyroid function in normal men.

To study the effect on thyroid function 100 mg of clomifene citrate was given once a day to two groups of healthy male volunteers for 5 and 12 consecutive days, respectively. In both groups serum concentrations of TSH, thyroxine, triiodothyronine, T3 resin uptake test and thyroid hormone binding proteins were measured before, during and after oral administration of clomifene. The effect of clomifene treatment was evaluated in Group 1 by means of serum FSH and LH measurements. Further in Group 2 the serum TSH response to iv TRH (200 microgram) was also investigated. The mean per cent elevations in serum concentrations of FSH and LH were 145 and 200, respectively. In Group 1 a small but statistically significant decrease within reference limits in triiodothyronine (P less than 0.01) and free thyroxine index (P less than 0.02) was found on day 4 of clomifene. On day 5 a slight increase in TSH was observed (P less than 0.05). In Group 2 the response of TSH to TRH showed a non-significant increase after 5 days and a significant increase (P less than 0.01) after 12 days of clomifene. Eight days after discontinuation of the drug the response was restored to normal. No changes in the thyroid hormone binding proteins in serum could be demonstrated. Though the observed changes were slight, they indicate that clomifene exerts an influence directly on the thyroid function.     

SPORADIC NON-TOXIC GOITRE: AN INVESTIGATION OF THE HYPOTHALAMIC–PITUITARY–THYROID AXIS

Thyrotrophin releasing hormone (TRH) tests have been carried out on sixty-two patients with sporadic non-toxic nodular goitre. 61% gave a subnormal thyroid stimulating hormone (TSH) response but had normal plasma thyroxine (T4) and triiodothyronine (T3) levels. T3 administration suppressed 131I uptake by the thyroid adequately in 74% of these and there was normal stimulation of thyroid uptake by exogenous TSH. Prolactin (PRL) rose normally after TRH in all the TRH non-responders. Normal TSH response to TRH was restored by partial thyroidectomy and in some cases by propyl thiouracil administration. Possible reasons for these findings are discussed. It is concluded that these cases were truly euthyroid.     

A new case of familial partial generalized resistance to thyroid hormones: study of 3,5,3'-triiodothyronine (T3) binding to lymphocyte and skin fibroblast nuclei and in vivo conversion of thyroxine to T3

A clinically euthyroid 30-yr-old man with high serum levels of both total (T4, 14.5 micrograms/dl; T3, 272 ng/dl) and free (FT4, 33 pg/ml; FT3, 9.7 pg/ml) thyroid hormones and inappropriately normal TSH levels, both basally and after TRH stimulation, is described. Peripheral indices of thyroid hormone action and the patient's clinical status were not modified by the prolonged administration of supraphysiological doses of both T4 (up to 900 micrograms/day) and T3 (up to 80 micrograms/day), which decreased but did not completely abolish the TSH response to TRH. However, the TSH response to TRH was normally blunted by dexamethasone administration, which also reduced serum T4 and T3 levels to normal. T3 binding to nuclei of mononuclear leukocytes and cultured skin fibroblasts was normal. The overall pattern demonstrates that the patient was affected by partial peripheral resistance to thyroid hormone action. Study of the patient's family revealed the same hormone pattern in the patient's father, suggesting an autosomal dominant mode of inheritance. An in vivo study performed after the iv injection of tracer doses of [125I]T4 and [131I]T3, demonstrated increased production rates (PR) of both T4 [PR, 113.0 micrograms/day X m2; normal subjects, 55.4 +/- 12.3 (mean +/- SD); n = 13] and T3 (PR, 41.1 micrograms/day X m2; normal subjects, 16.3 +/- 2.7). In vivo conversion of T4 to T3 was also evaluated in the patient; a nearly normal T4 to T3 conversion factor was found (0.3108 vs. 0.2576 +/- 0.0422 in normal subjects). In four hyperthyroid patients, the T4 to T3 conversion factors were similar (0.2932 +/- 0.0600), while the PRs of T4 and T3 were increased (PR of T4, 308.6 +/- 85.6; PR of T3, 110.3 +/- 35.0 micrograms/day X m2) compared to those in the normal subjects.     

THE TRIIODOTHYRONINE AND THYROXINE RESPONSE TO THYROTROPHIN-RELEASING HORMONE IN THE ASSESSMENT OF THE PITUITARY-THYROID AXIS

The thyroidal component of the response to thyrotrophin releasing hormone (TRH) has been studied by measurement of serum triiodothyronine (T3) and thyroxine (T4).
In normal subjects a significant increase in serum T3 followed intravenous administration of TRH 200 μg. A less consistent increase was detected in serum T4 concentration.
Oral TRH at a dose of 40 mg caused a significant rise in serum T4 in normal subjects. The increase in T4 at 24 hr was considered to provide a convenient index of pituitary and thyroidal response.
Fourteen patients with pituitary disease, of whom twelve were euthyroid, were investigated by an oral TRH test. The majority of these patients retain a normal pituitary TSH reserve though a small group can be identified in whom it is diminished.
A significant correlation was obtained between the T4 and TSH response to oral TRH. It is suggested that measurement of serum concentration of thyroid hormone is of value in the assessment of the pituitary response to TRH and the integrity of the pituitary-thyroid axis.