Clinical implications of imprecise sampling time for 10- and 30-min thyrotropin-releasing hormone stimulation tests in horses

BACKGROUND

The thyrotropin-releasing hormone (TRH) stimulation test is used to diagnose pituitary pars intermedia dysfunction (PPID) using 10- or 30-min protocols. Imprecise sampling time for the 10-min protocol can lead to misdiagnoses.

OBJECTIVES

To determine the effect of imprecise sampling time for the 30-min protocol of the TRH stimulation test.

STUDY DESIGN

In vivo experiment.

METHODS

Plasma immunoreactive adrenocorticotropin (ACTH) concentrations were measured 9, 10, 11, 29, 30 and 31 min after intravenous administration of 1 mg of TRH in 15 control and 12 PPID horses. Differences in ACTH concentrations between sampling times, variability in ACTH concentrations between protocols, and diagnostic classification of PPID were assessed using Friedman's test, Bland-Altman plots, and Fisher's exact test, respectively, with 95% confidence intervals reported and significance set at p < 0.05.

RESULTS

Imprecise sampling time resulted in variable ACTH concentrations, but significant differences in absolute ACTH concentrations were not detected for imprecise sampling within each protocol or between protocols. Imprecise sampling changed PPID diagnostic classification for 3/27 (11 [4-28] %) horses for both protocols. Using the 30-min protocol as a reference, 1/12 (8 [1-35] %) horses returned a negative test result and 5/12 (42 [19-68] %) horses returned equivocal test results that would be considered positive in practice due to the presence of supportive clinical signs.

MAIN LIMITATIONS

Limited sample size and inter-horse variability reduced the ability to detect small but potentially relevant differences.

CONCLUSIONS

Overall, the impact of imprecise sampling was not significantly different between the 10- and 30-min TRH stimulation test protocols. However, diagnostic classification for PPID would have varied between the 10- and 30-min protocols in this population, if clinical signs had been ignored. Precise timing during TRH stimulation tests and contextual interpretation of ACTH concentrations remain fundamental for the diagnosis of PPID.

Unique tRNA Fragment Upregulation with SARS-CoV-2 but Not with SARS-CoV Infection

Unlike other coronaviruses, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly infected the global population, with some suffering long-term effects. Thanks to extensive data on SARS-CoV-2 made available through global, multi-level collaborative research, investigators are getting closer to understanding the mechanisms of SARS-CoV-2 infection. Here, using publicly available total and small RNAseq data of Calu3 cell lines, we conducted a comparative analysis of the changes in tRNA fragments (tRFs; regulatory small noncoding RNAs) in the context of severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2 infections. We found extensive upregulation of multiple tRFs in SARS-CoV-2 infection that was not present in SARS-CoV or other virus infections our group has studied. By comparing the total RNA changes in matching samples, we identified significant downregulation of TRDMT1 (tRNA methyltransferase), only in SARS-CoV-2 infection, a potential upstream event. We further found enriched neural functions among downregulated genes with SARS-CoV-2 infection. Interestingly, theoretically predicted targets of the upregulated tRFs without considering mRNA expression data are also enriched in neural functions such as axon guidance. Based on a combination of expression data and theoretical calculations, we propose potential targets for tRFs. For example, among the mRNAs downregulated with SARS-CoV-2 infection (but not with SARS-CoV infection), SEMA3C is a theoretically calculated target of multiple upregulated tRFs and a ligand of NRP1, a SARS-CoV-2 receptor. Our analysis suggests that tRFs contribute to distinct neurological features seen in SARS-CoV-2.

Diagnosis of equine pituitary pars intermedia dysfunction

Equine pituitary pars intermedia dysfunction (PPID) is common in aged horses. The majority of horses respond well to treatment, but treatment is lifelong, meaning accurate diagnosis of PPID is important. Similar to any condition, there is no perfect laboratory test to diagnose PPID and accuracy is affected by the characteristics of the population in which the test is being evaluated. This review details the importance of consideration of clinical factors and diagnostic test accuracy. Basal adrenocorticotrophic hormone (ACTH) concentration is used most frequently in practice and has very good diagnostic accuracy when used in combination with clinical judgement and the correct application of diagnostic thresholds. The thyrotropin-releasing hormone stimulation test can be used in horses with equivocal test results following basal ACTH testing, or to evaluate subtle cases due to its improved accuracy.

Effects of Intermittent Fasting on Hypothalamus-Pituitary-Thyroid Axis, Palatable Food Intake, and Body Weight in Stressed Rats

Dietary regimens that are focused on diminishing total caloric intake and restricting palatable food ingestion are the most common strategies for weight control. However, restrictive diet therapies have low adherence rates in obese patients, particularly in stressed individuals. Moreover, food restriction downregulates the hypothalamic-pituitary-thyroid axis (HPT) function, hindering weight loss. Intermittent fasting (IF) has emerged as an option to treat obesity. We compared the effects of IF to an all-day feeding schedule on palatable diet (PD)-stress (S)-induced hyperphagia, HPT axis function, accumbal thyrotropin-releasing hormone (TRH), and dopamine D2 receptor expression in association with adipocyte size and PPARƔ coactivator 1α (PGC1α) and uncoupling protein 1 (UCP1) expression in stressed vs. non-stressed rats. After 5 weeks, S-PD rats showed an increased energy intake and adipocyte size, fewer beige cells, and HPT axis deceleration-associated low PGC1α and UCP1 expression, as well as decreased accumbal TRH and D2 expression. Interestingly, IF reversed those parameters to control values and increased the number of beige adipocytes, UCP1, and PGC1α mRNAs, which may favor a greater energy expenditure and a reduced body weight, even in stressed rats. Our results showed that IF modulated the limbic dopaminergic and TRHergic systems that regulate feeding and HPT axis function, which controls the metabolic rate, supporting this regimen as a suitable non-pharmacologic strategy to treat obesity, even in stressed individuals.

Bexarotene-induced central hypothyroidism assessed by TRH stimulation test in cutaneous T-cell lymphoma patients

Bexarotene-induced central hypothyroidism (CH), for which levothyroxine (LT4) replacement is recommended, has been shown to be caused by pituitary but not hypothalamic disorder experimentally, though the underlying mechanism in humans remains unclear. Here, the pathophysiology of bexarotene-induced CH was examined using a TRH stimulation test in cutaneous T-cell lymphoma (CTCL) patients. In this retrospective longitudinal observational study, serum TSH and free T4 (F-T4) levels were measured in 10 euthyroid patients with CTCL during 24 weeks of bexarotene treatment. TRH stimulation testing was performed following CH diagnosis, with LT4 replacement dosage adjusted to maintain F-T4 at the pre-treatment level. After one week of bexarotene administration, all 10 patients developed CH, based on combined findings of low or low-normal F-T4 with low or normal TSH levels. TSH peak response after a stimulation test at one week was reached at 30 minutes. However, that was <4 μIU/mL in all patients, indicating a blunted though not exaggerated and delayed TSH response. In eight who continued bexarotene for 24 weeks, median LT4 replacement dosage was 125 (range, 75-150) μg/day. TSH level at 30 as well as 15, 60, 90, and 120 minutes after TRH stimulation was significantly correlated with LT4 replacement dosage (ρ = -0.913, p = 0.002), whereas TSH and F-T4 basal levels at one week were not. These results suggest that pituitary hypothyroidism is responsible for bexarotene-induced CH, while TSH levels after TRH stimulation precisely reflect residual pituitary-thyroid function in patients receiving bexarotene.

Enhancing the Natural Biological Control in the Thyroid Hormone Homeostasis As a First-Order Control System

This study explores the natural control system that exists within the pituitary gland. More specifically, this study investigates the regulation of the thyroid stimulating hormone (TSH), released by the anterior pituitary, with regards to the thyroid releasing hormone (TRH), which is released by the hypothalamus. Using appropriate assumptions on the behavior of the hormones, along with relevant boundary conditions, we modeled an output of TSH using constant TRH input over the course of a six-hour period. Other relevant hormones such as thyroxine (T4), triiodothyronine (T3), and their relevant intermediaries were also modeled as a means to complete the natural feedback found physiologically. Due to our boundary conditions, we do not consider the consumption or final function of these hormones since they leave the pituitary gland, our control system; instead, we consider a constant TRH since it is produced by the hypothalamus. Finally, we explore the results of reducing the TRH input while observing the TSH response. We append a short loop controller feedback that uses the TSH output to regulate a TRH input to remedy the reduction of TRH. The open-loop transfer function derived presented three poles at the clearance exponents for T4, TSH, and central T3, with a phase margin of 74.1°, characterizing a stable but slow system that can be improved with a simple proportional control.

Evolution of thyrotropin-releasing factor extracellular communication units

Thyroid hormones (THs) are ancient signaling molecules that contribute to the regulation of metabolism, energy homeostasis and growth. In vertebrates, the hypothalamus-pituitary-thyroid (HPT) axis links the corresponding organs through hormonal signals, including thyrotropin releasing factor (TRF), and thyroid stimulating hormone (TSH) that ultimately activates the synthesis and secretion of THs from the thyroid gland. Although this axis is conserved among most vertebrates, the identity of the hypothalamic TRF that positively regulates TSH synthesis and secretion varies. We review the evolution of the hypothalamic factors that induce TSH secretion, including thyrotropin-releasing hormone (TRH), corticotrophin-releasing hormone (CRH), urotensin-1-3, and sauvagine, and non-mammalian glucagon-like peptide in metazoans. Each of these peptides is part of an extracellular communication unit likely composed of at least 3 elements: the peptide, G-protein coupled receptor and bioavailability regulator, set up on the central neuroendocrine articulation. The bioavailability regulators include a TRH-specific ecto-peptidase, pyroglutamyl peptidase II, and a CRH-binding protein, that together with peptide secretion/transport rate and transduction coupling and efficiency at receptor level shape TRF signal intensity and duration. These vertebrate TRF communication units were coopted from bilaterian ancestors. The bona fide elements appeared early in chordates, and are either used alternatively, in parallel, or sequentially, in different vertebrate classes to control centrally the activity of the HPT axis. Available data also suggest coincidence between apparition of ligand and bioavailability regulator.

Response of preterm infants with transient hypothyroxinaemia of prematurity to the thyrotropin-releasing hormone stimulation test is characterized by a delayed decrease in thyroid-stimulating hormone after the peak

OBJECTIVES

We evaluated the response to the thyrotropin-releasing hormone (TRH) stimulation test in very low-birth weight (VLBW) infants to elucidate the aetiology of transient hypothyroxinaemia of prematurity (THOP).

DESIGN AND METHODS

We performed TRH stimulation tests on 43 VLBW infants. Subjects were divided into two groups; a THOP group (N = 11; basal TSH < 15 mU/L and basal FT4 ≤ 0.8 ng/dL) and a non-THOP group (N = 32; basal TSH < 15 mU/L and basal FT4 > 0.8 ng/dL). Basal FT4 and FT3 were measured before, and TSH (0, 30, 60, 90, 120 and 180 minutes) was measured after, the administration of TRH (7 µg/kg). We calculated the ratio of TSH 180 minutes to THS 0 minute as the primary outcome. We also collected data on T3 and rT3 in this study.

RESULTS

In both groups, TSH 30 minutes values were the highest. However, the ratios of TSH 180 minutes to THS 0 minutes in the non-THOP group and the THOP group were (median [IQR]) 1.3 [1.0-1.7] and 3.0 [1.5-5.3] (P < .01). No significant differences were observed in T3 (1.0 [0.8-1.3] and 0.7 [0.4-0.7] ng/mL, P = .06). However, in the THOP group, rT3 was significantly lower than that of the non-THOP group (168.0 [148.1-197.0] and 92.9 [74.7-101.6] pg/mL, P < .01).

CONCLUSIONS

The delayed decrease in the TSH concentration after the peak for the TRH tests and decreased levels of rT3 suggest that the main aetiology for THOP is suppression at the level of the hypothalamus, but not inactivation of peripheral thyroid hormone metabolism.

Abnormal thyroid hormone response to TRH in a case of macro-TSH and the cut-off value for screening cases of inappropriate TSH elevation

A 74-year-old asymptomatic Japanese man with suspected thyroid dysfunction was referred to our hospital. He had an elevated TSH (53.8 mIU/L; reference interval: 0.5-5.0) despite a free T4 (FT4) level (1.4 ng/dL; reference interval: 0.9-1.6). Further analysis revealed macro-TSH. A notable finding was that a 500-μg TRH stimulation test revealed a blunted free T3 (FT3) response despite a prolonged TSH response. Macro-TSH typically presents with inappropriately marked elevation of serum TSH levels compared with other thyroid hormones, as exhibited in our case. However, the level of TSH elevation that might differentiate macro-TSH from subclinical hypothyroidism is poorly known. We retrospectively analyzed 8,183 concurrent measurements of TSH and FT4 in individuals previously examined in our hospital to define the cut-off value for screening cases of inappropriate TSH elevation. FT4 values were rounded off to one decimal place, and the 97.5th percentile of TSH against each FT4 value was calculated. The data of our patient and that of 30 cases of macro-TSH extracted from the English literature were then assessed. When the approximate curve obtained from the 97.5th percentile of TSH values was defined as the cut-off value [Log₁₀TSH = 0.700 + 1.549/{1 + (FT4/0.844)^6.854}], 25 of the 31 (80.6%) macro-TSH cases were identified. In conclusion, we report for the first time a case of macro-TSH demonstrating an abnormal FT3 response to TRH. A cut-off value of TSH adjusted to the FT4 level may be a good method of screening for inappropriate TSH elevation (or inappropriate hyperthyrotropinemia) including those caused by macro-TSH.

Response to thyrotropin-releasing hormone (TRH) in a horse with hyperthyroidism associated with a functional thyroid adenoma

A 16-year-old American Paint Horse gelding was presented for evaluation of weight loss and high serum thyroid hormone concentrations resulting from a functional thyroid adenoma. The horse showed no response to a thyrotropin-releasing hormone (TRH) stimulation test. Clinical signs resolved following surgical removal of the adenoma.

Variant Prolactin Receptor in Agalactia and Hyperprolactinemia

A loss-of-function variant in the gene encoding the prolactin receptor ( PRLR) was reported previously in a woman with persistent postpartum galactorrhea; however, this paradoxical phenotype is not completely understood. Here we describe a 35-year-old woman who presented with idiopathic hyperprolactinemia that was associated with a complete lack of lactation after each of her two deliveries. She is a compound heterozygote for loss-of-function variants of PRLR. Her unaffected parents are heterozygotes. These findings are consistent with previous work showing that mice deficient in functional Prlr do not lactate.

Evaluation of growth hormone-releasing peptide-2 for diagnosis of thyrotropin-producing pituitary adenomas

Thyrotropin (TSH)-producing adenomas are a rare cause of hyperthyroidism and are a type of functional pituitary adenoma. The diagnosis of TSH-producing adenoma is a challenging problem in clinical endocrinology. Since growth hormone-releasing peptide-2 (GHRP-2) fails to induce TSH secretion in normal subjects, the effect of GHRP-2 on TSH levels was therefore examined in patients with TSH-producing adenomas. A total of 5 patients (4 women and 1 man) referred to our departments for further evaluation of pituitary hormones were followed-up using the GHRP-2, TSH-releasing hormone (TRH), octreotide, and bromocriptine tests to examine and evaluate TSH secretory dynamics in TSH-producing adenomas. Of 5 patients, 2 (40%) showed such a significant response, defined as a >50% increase in serum TSH level above baseline in the GHRP-2 test. Additionally, 1 patient showed a 48% increase in serum TSH level. In 1 patient whose adenoma was completely removed, basal serum concentrations of TSH were sufficiently suppressed after the operation, and serum TSH levels failed to increase in response to GHRP-2 administration. In 4 patients (80%), a poor response of serum TSH levels was observed in the TRH test. In 2 out of 5 patients (40%), serum TSH levels were significantly decreased following octreotide administration. No patient demonstrated a significant response to the bromocriptine test. In addition to TRH test, the GHRP-2 test as a potential diagnostic tool for TSH-producing pituitary adenomas.

Usefulness of the Trh Test in the Management of Patients with Differentiated Thyroid Cancer

Thirty patients thyroidectomized for differentiated thyroid cancer were studied. Serum TSH was assayed in basal conditions and after TRH stimulation, while patients were in suppressive therapy with thyroid hormones. The basal TSH was normal in all the patients and less than 2 μ/ml in 20 patients. The TRH test was negative (no TSH response) in 27 patients and in all the cases with the basal TSH lower than 2 μU/ml.

Serum Prolactin Levels in Women with Gross Cystic Breast Disease

Serum prolactin (PRL) concentrations at baseline and after TRH stimulation were determined in 15 healthy women and in 51 premenopausal patients suffering from Gross Cystic Breast Disease. All women were in the luteal phase of the menstrual cycle and patients were divided into three groups according to cyst type at presentation. Basal hormone levels were within the normal range in the control group and in the three cystic breast disease groups. The maximum PRL response to TRH stimulation was significantly higher (p < 0.001) in patients with type I cysts (low Na+/K+ intracystic ratio and apocrine epithelium) than in patients with type II cysts (high Na+/K+ intracystic ratio and flattened epithelium), type III cysts (intermediate Na+/K+ intracystic ratio and mixed epithelium) and in normal women. Serum PRL concentrations corresponding to samples obtained 60 and 90 minutes after stimulation remained higher in the first group of patients. These results led us to consider the existence of an altered central regulation of PRL secretion in patients with type I cysts at presentation.

Clinical and genetic characteristics of a large monocentric series of patients affected by thyroid hormone (Th) resistance and suggestions for differential diagnosis in patients without mutation of Th receptor β

OBJECTIVE

The syndrome of resistance to thyroid hormone (RTH) is caused by a mutation of TH receptor β (TRβ) in 80% of cases. Patients without mutation (non-TR-RTH) may have a biochemical pattern that is difficult to differentiate from that of pituitary TSH-secreting adenoma (TSHoma). Herein, we report a large monocentric series of RTH focusing on patients with non-TR-RTH, to evaluate possible clinical or biochemical parameters able to distinguish them from TSHoma.

DESIGN AND PATIENTS

We retrospectively reviewed the data of 99 consecutive patients with inappropriate TSH secretion (IST) syndrome referred to our Department between 1983 and 2011, identifying 68 patients with RTH and 31 patients with TSHomas.

MEASUREMENTS

Patient records were reviewed for the main clinical, biochemical and imaging characteristics.

RESULTS

Of our 68 patients with RTH, 16 (23·5%) did not show a TRβ mutation and did not have affected family members. Of these 16 patients, three developed a TSHoma, during follow-up. To distinguish non-TR-RTH from TSHoma, we identified appropriate cut-off values for the main biochemical parameters that demonstrated the greatest sensitivity and specificity (T3 suppression test, α-subunit/TSH molar ratio, α-subunit assay and TRH test) and we calculated the probability for each patient to develop a TSHoma.

CONCLUSIONS

The application of the identified cut-offs could become a very useful tool in the challenging differential diagnosis between sporadic non-TR-RTH and TSHoma. It would then be possible to select the patients at higher risk of developing a TSHoma and therefore needing a closer follow-up.

Coordination of hypothalamic and pituitary T3 production regulates TSH expression

Type II deiodinase (D2) activates thyroid hormone by converting thyroxine (T4) to 3,5,3'-triiodothyronine (T3). This allows plasma T4 to signal a negative feedback loop that inhibits production of thyrotropin-releasing hormone (TRH) in the mediobasal hypothalamus (MBH) and thyroid-stimulating hormone (TSH) in the pituitary. To determine the relative contributions of these D2 pathways in the feedback loop, we developed 2 mouse strains with pituitary- and astrocyte-specific D2 knockdown (pit-D2 KO and astro-D2 KO mice, respectively). The pit-D2 KO mice had normal serum T3 and were systemically euthyroid, but exhibited an approximately 3-fold elevation in serum TSH levels and a 40% reduction in biological activity. This was the result of elevated serum T4 that increased D2-mediated T3 production in the MBH, thus decreasing Trh mRNA. That tanycytes, not astrocytes, are the cells within the MBH that mediate T4-to-T3 conversion was defined by studies using the astro-D2 KO mice. Despite near-complete loss of brain D2, tanycyte D2 was preserved in astro-D2 KO mice at levels that were sufficient to maintain both the T4-dependent negative feedback loop and thyroid economy. Taken together, these data demonstrated that the hypothalamic-thyroid axis is wired to maintain normal plasma T3 levels, which is achieved through coordination of T4-to-T3 conversion between thyrotrophs and tanycytes.

The thyrotropin-releasing hormone test may predict recurrence of clinical depression within ten years after discharge

OBJECTIVES

The underlying pathogenic mechanisms and predictors of recurrence in major depressive disorder are still largely unknown. Hypothalamic-pituitary-thyroid (HPT) axis and hypothalamus-pituitary-adrenocortical (HPA) axis dysregulation are thought to be related to the development and course of depression.

DESIGN AND SETTING

Over a ten-year period, we investigated whether the results of thyrotropin-releasing hormone (TRH) testing and combined dexamethasone/corticotropin-releasing hormone (DEX/CRH) testing could be correlated with the recurrence of depression in 25 outpatients with clinically remitted major depression for at least 10 years.

MATERIALS AND METHODS

Twenty-five patients (16 women and 9 men, 48.1 years of age, SD=11.4, range 22-84) with major depressive disorder were available for evaluation during hospitalization. TRH and DEX/CRH tests were administered at admission.

RESULTS

Patients who recurred within ten years after remission exhibited significantly higher thyroid stimulating hormone (TSH) responses to TRH at the time of admission compared to those who did not recur. There was no significant correlation between recurrence and DEX/CRH levels after controlling for age, sex, and body mass index.

CONCLUSION

The findings of this study suggest that the TRH test may predict future recurrence in patients with depression.

A marked difference in the vasopressin responsiveness between the adrenal glands in a patient with adrenocorticotropin-independent macronodular adrenal hyperplasia

We herein present the case of a 53-year-old patient with adrenocorticotropin-independent macronodular adrenocortical hyperplasia (AIMAH), which is a rare form of Cushing syndrome. He had hypercortisolemia and bilateral macronodular adrenal glands with a left side predominance. The administration of vasopressin significantly increased the plasma cortisol level (1.9-fold). Following left adrenalectomy, the patient's hypercortisolemia significantly improved and vasopressin responsiveness was lost, suggesting that the responsiveness originated from the resected left adrenal gland. The marked difference in vasopressin responsiveness between the adrenals corresponded with their asymmetrical size and function. Evaluating the differences in the vasopressin sensitivity may therefore be helpful for understanding the progression of AIMAH.

[Resistance to thyroid hormone and Hashimoto's thyroiditis]

BACKGROUND

Resistance to thyroid hormone (RTH) is a rare condition characterized by elevation of thyroid stimulating hormone (TSH) and thyroid hormones (TH). Its association with Hashimoto's thyroiditis was described in 1993 and occurs in 1 of 1.3 million births.

CLINICAL CASE

We present a female patient with a family history of hypothyroidism. The patient's condition began in 2008 with symptoms of hyperthyroidism, elevated triiodothyronine (T3), thyroxine (T4) and TSH levels. Thyroid scan showed hypermetabolic activity and she was positive for anti-peroxidase antibodies (anti-TPO). After administration of thiamazole, TSH increased. In 2009 she was diagnosed with clinical hypothyroidism, high levels of TSH, and normal T3 and T4 levels. Levothyroxine was prescribed but TSH increased and she presented clinical signs of hyperthyroidism. Patient abandoned treatment after 1 month. Her symptoms fluctuated among hyperthyroidism, euthyroidism and hypothyroidism. In 2010 she presented tachycardia, weight loss, and high T3, T4 and TSH levels. Thyrotropin-secreting adenoma (TSHoma) was suspected and ruled out by magnetic resonance imaging (MRI). Thyrotropin releasing hormone (TRH) test was performed. TSH increased and the α-subunit of pituitary hormones retained low levels.

CONCLUSIONS

RTH diagnosis requires exclusion of a TSHoma because both present a similar pattern according to thyroid tests. The association between Hashimoto's thyroiditis and RTH is not well known. This pathological condition has a mutated TRβ gene in 75% of the cases.

Evaluation of thyroid functions with respect to iodine status and TRH test in chronic autoimmune thyroiditis

OBJECTIVE

Chronic autoimmune thyroiditis (CAT) is the most common form of thyroiditis in childhood and a frequent cause of acquired hypothyroidism. The objective of this study was to evaluate the thyroid status of children and adolescents with CAT with respect to iodine status and diagnostic values of thyrotropin-releasing hormone (TRH) test.

METHODS

Seventy-one children (mean age: 11.6 years) were studied in a retrospective analysis. Free thyroxine (T4), thyrotropin (TSH), TSH response to TRH test, thyroid autoantibodies, thyroid sonography, and urinary iodine excretion (UIE) were evaluated.

RESULTS

At diagnosis, 8.5% of patients had overt hypothyroidisim and 36.6% subclinical hypothyroidism; 5.6% had overt hyperthyroidisim and 8.5% had subclinical hyperthyroidism. Of them, 40.8% were euthyroid. Median UIE was 51 mg/L in overt hypothyroidism and 84 mg/L in subclinical hypothyroidism. The values were 316 mg/L and 221 mg/L in overt and subclinical hyperthyroidism, respectively. Basal TSH showed a strong correlation with peak TSH level on TRH test. Thirty-four percent of patients with normal basal TSH level showed an exaggerated TSH response.

CONCLUSION

Iodine deficiency was seen more in cases with hypothyroidism, while excess of iodine was observed to be more frequent in hyperthyroid patients. Iodine status was a strong predictorof the thyroid status in CAT. TRH test may be helpful in further delineating patients with subclinical hypothyroidism.

The Thr92Ala 5' type 2 deiodinase gene polymorphism is associated with a delayed triiodothyronine secretion in response to the thyrotropin-releasing hormone-stimulation test: a pharmacogenomic study

BACKGROUND

The common Thr92Ala D2 polymorphism has been associated with changes in pituitary-thyroid axis homeostasis, but published results are conflicting. To investigate the effects of the Thr92Ala polymorphism on intrathyroidal thyroxine (T4) to triiodothyronine (T3) conversion, we designed prospective pharmacogenomic intervention aimed to detect differences in T3 levels after thyrotropin (TSH)-releasing hormone (TRH)-mediated TSH stimulation of the thyroid gland.

METHODS

Eighty-three healthy volunteers were screened and genotyped for the Thr92Ala polymorphism. Fifteen volunteers of each genotype (Thr/Thr, Thr/Ala, and Ala/Ala) underwent a 500 mcg intravenous TRH stimulation test with serial measurements of serum total T3 (TT3), free T4, and TSH over 180 minutes.

RESULTS

No differences in baseline thyroid hormone levels were seen among the study groups. Compared to the Thr/Thr group, the Ala/Ala group showed a significantly lower TRH-stimulated increase in serum TT3 at 60 minutes (12.07 ± 2.67 vs. 21.07 ± 2.86 ng/dL, p = 0.029). Thr/Ala subjects showed an intermediate response. Compared to Thr/Thr subjects, the Ala/Ala group showed a blunted rate of rise in serum TT3 as measured by mean time to 50% maximum delta serum TT3 (88.42 ± 6.84 vs. 69.56 ± 6.06 minutes, p = 0.028). Subjects attained similar maximal (180 minutes) TRH-stimulated TT3 levels. TRH-stimulated TSH and free T4 levels were not significantly different among the three genotype groups.

CONCLUSIONS

The commonly occurring Thr92Ala D2 variant is associated with a decreased rate of acute TSH-stimulated T3 release from the thyroid consistent with a decrease in intrathyroidal deiodination. These data provide a proof of concept that the Thr92Ala polymorphism is associated with subtle changes in thyroid hormone homeostasis.

Gender differences in serum GH and IGF-I levels and the GH response to dynamic tests in patients with acromegaly

Gender affects the GH secretory pattern both in normal subjects and in patients with acromegaly by an uncertain mechanism. Here, we report the influence of gender on the relationship between serum GH and IGF-I levels and the GH response to dynamic tests in patients with acromegaly. Seventy-four patients with untreated acromegaly (M/F 27/47, age range 22-86 yr.) were studied. The serum GH levels did not differ between male and female (6.1 vs. 8.7 ng/ml; p=0.26), while serum IGF-I levels, IGF-I SDS and the IGF-I/GH ratio were lower in female than those in male (679 vs. 769 ng/ml; p<0.02, 7.3 vs. 9.2 SDS; p<0.02 and 79.6 vs. 141.5; p<0.05). When the subjects were divided into two groups: age <or=50 yr, and age >50 yr, serum IGF-I levels and IGF-I/GH ratios were lower in female than those in male in patients <or=50 yrs (650 vs. 1002 ng/ml; p<0.05 and 59.8 vs. 142.9; p<0.05), but not in patients >50 yrs (684 vs. 680 ng/ml; p=0.39 and 98.7 vs. 118.4; p=0.40). The GH responses to OGTT, TRH, octreotide, and bromocriptine tests were similar in male and female. In conclusion, IGF-I/GH ratio was significantly lower in female than that in male particularly in younger patients with acromegaly. These data suggest that gender, presumably sex steroids in female, may partially modulate the relationship between circulating IGF-I and GH levels in patients with acromegaly.

Is there an undiscovered neurocircuit for regulating GH secretion? -Pitfalls of GHRP-2 and ITT as GH provocative tests-

GH secretion is mainly regulated at the hypothalamus by a dual interplay between growth hormone releasing hormone (GHRH) and somatostatin, which are modulated by various factors. We examined the regulatory mechanism of GH secretion in an apparently healthy young man without decreased IGF-1 concentration and nocturnal GH secretion, but who showed low responses to insulin tolerance (ITT) and to GHRP-2 tests. The patient also had no GH response to acute aerobic exercise. However, he had normal secretion of pituitary hormone based on hypothalamic releasing hormone tests combined with CRH, GRH as GHRH, LH-RH and TRH. In addition, he had a GH response without paradoxical secretion to TRH stimulation as well as an ACTH response to subcutaneous glucagon stimulation, and AVP secretion responded to 5% hypertonic saline infusion, though it was not adequately stimulated by ITT. MRI showed no structural abnormalities in the hypothalamus-pituitary gland. These findings indicate that this subject may have an undiscovered neurocircuit for regulating GH secretion, as well as other neurohormones, to maintain homeostasis, even though there were low responses of the hormones to ITT and GHRP-2 stimuli, probably via altered secretion of hypothalamic hormones.

Reference intervals for serum thyrotropin: dependence on the population investigated

In order to elucidate possible differences of reference intervals in various populations, serum basal thyrotropin (TSH) was measured in euthyroid healthy volunteers (N = 170), in thyroid out-patients (N = 215), in geriatric (N = 354) and in seriously ill (N = 32) patients. The results, except in the healthy control subjects, were compared to the TSH responses (delta TSH) in the Thyrotropin Releasing Hormone test. Normal ranges calculated from the basal TSH of the euthyroid groups of different age were similar. There was a significant positive correlation of basal to delta TSH in all groups but the regression equations expressing the qualitative connection of basal and delta TSH were rather different. The basal TSH cut off point predicting a positive TRH-test (i.e. euthyroidism) with more than 95% probability was higher in the geriatric groups (greater than 0.7 mU/l versus greater than 0.4 mU/l in the other groups). In thyroid out-patients and geriatric patients a measurable (greater than 0.1 mU/l) basal TSH indicated measurable delta TSH (thus excluding clinical hyperthyroidism), while in seriously ill patients only a basal TSH greater than 0.2 mU/l was reliably predictive in this respect. Thus, various populations have different reference intervals for TSH. This fact must be considered when the sensitive TSH is used in different populations as the primary screening parameter for thyroid dysfunctions.

Naloxone influence on the growth hormone, prolactin and thyrotropin response to thyrotropin releasing hormone in acromegalic patients

In order to gain insight into the neuroendocrine mechanism underlying the paradoxical GH response to TRH in acromegalic patients, we have investigated the effect of an infusion of Naloxone (Nal, 1.6 mg/hr for two hours), on a TRH test performed both in responder (n = 9) and non-responder (n = 5) acromegalic patients. The response of GH, PRL and TSH to TRH injection were evaluated. NAL did not exert significant variations in the GH response, even if different patterns of GH response during NAL were observed in the group of TRH-responder patients. Similarly, TRH-induced PRL response was not significantly affected by the infusion of an opiate antagonist. On the contrary, a significant inhibition of the TSH response was observed in the group of TRH-responder patients (delta TSH after TRH 4.76 +/- 1.11 microU/ml, after NAL + TRH 2.81 +/- 0.99 microU/ml, p < 0.05). No significant effects were observed in the TRH non-responder patients (delta TSH after TRH 4.58 +/- 1.44 microU/ml, after NAL + TRH 6.26 +/- 3.27 microU/ml). The differences observed in the two groups of patients could be ascribed to a different endogenous somatostatinergic tone and could furnish a prognostic indication in acromegalic patients.

TSH response pattern to TRH test and optimum time of blood sampling in sporadic euthyroid goitre

Attempts were made to estimate the response pattern of thyrotrophin (TSH) to thyrotrophin-releasing hormone (TRH) and the optimum time of blood sampling in patients with sporadic euthyroid goitre. Of the 65 subjects studied, 21 served as a reference group and 44 were patients with sporadic euthyroid goitres, divided into diagnostic subgroups according to type of goitre. Patients with a single autonomous thyroid adenoma were excluded. The classification of goitre was based on clinical features, thyroid function tests, thyroid imaging studies using 99mTc pertechnetate uptake, and examination of thyroid specimens originating from selective goitre resection carried out after the laboratory investigations. A standardized i.v. TRH test was performed in all probands and the TSH response was followed for 60 min postinjection. There was a definite trend towards lack of response with increasing nodularity of the thyroid gland. Moreover, no further information concerning the TSH response pattern was achieved by extending the blood sampling period beyond the +20 min limit of the time axis. The study lends support to the view that increasing functional autonomy is a general trend in goitre evolution.

The effect of long-term cimetidine treatment on PRL and TSH response capacity to TRH in male patients with duodenal ulcer

The effect of long-term cimetidine treatment for 6 months on basal and thyrotropin-releasing hormone (TRH)-stimulated prolactin (PRL) and thyroid-stimulating hormone (TSH) secretion was studied in eight male patients with duodenal ulcer. They received 1,000 mg cimetidine orally per day until ulcer healing and thereafter 400 mg daily for the remaining period. TRH perturbation tests were performed before and after the 6 months of treatment. A significant reduction in the pituitary TSH response capacity was found. No significant changes in basal and TRH-stimulated PRL, basal TSH, thyroxine and triiodothyronine were found. It is uncertain if the reduction in pituitary TSH response capacity has any clinical implications in euthyroid patients.

Thyroid function in malignant lymphoma

Thyroid function was studied in 36 patients with various stages of malignant lymphoma. Stage IVB patients exhibited characteristic changes in thyroid biochemistry in the form of lowered triiodothyronine (T3) and elevated free thyroxine (FT4), but normal thyroxine. Moreover, the concentration of thyroxine-binding prealbumin and albumin was lowered, whereas thyroxine-binding globulin was normal. Thyroid-stimulating hormone was slightly elevated but showed a normal increase after administration of thyrotrophin-releasing hormone. Patients with less extensive disease differed only slightly from the controls. The results agree with previous studies of patients suffering from other chronic diseases. The mechanisms underlying the hormonal changes have been only partially elucidated. When investigating patients with disseminated malignant disease for thyroid disease, the above mentioned changes in thyroid biochemistry must be borne in mind. Single analyses of FT4 and T3 may give rise to a false assumption of hyper- or hypothyroid states in patients who are in fact euthyroid.

Assessment of thyroid function in chronic alcoholics

The clinical manifestations in chronic alcoholics may sometimes mimic those of hyperthyroidism. However, diagnostic aids are somewhat contradictory in many cases. Ten chronic alcoholics with symptoms from the sympathoadrenal system were investigated. A significant increase (p less than 0.01) of T3 at 120 min after TRH stimulation was found despite a blunted TSH response (increment less than 3 mU/l) in some cases. This increase in T3 indicates a preserved thyroid function in chronic alcoholics despite generally low basal T3 levels. It is concluded that T3 determinations at 120 min in connection with TRH test may be an essential parameter in evaluating euthyroid function in chronic alcoholics.

Normal growth hormone secretion is rare after microsurgical normalization of growth hormone levels in acromegaly

The effect of microsurgery on growth hormone (GH) secretion was studied in 34 patients with acromegaly. All patients showed enlarged sella volumes according to encephalography and macroadenomas at surgery. Preoperative GH levels were elevated in all 34 patients and 14 had concomitant hyperprolactinemia. There was a correlation between basal GH levels and sella size. Visual field defects, suprasellar extension, long duration of the disease, hyperprolactinemia and aneuploidy were noted in patients with low as well as high levels of GH preoperatively. The average reduction of GH levels in the total series was 71 +/- 21% (mean +/- SD). A notably similar reduction of GH levels was seen regardless of preoperative GH levels, concomitant hyperprolactinemia, visual field defects, size of the adenoma, invasive growth or increasing experience of the surgeon. Therefore, normal GH levels after surgery were reached mainly in patients with moderate GH increments preoperatively. GH levels were normalized by surgery in 15 patients but only four of these showed normal GH response to TRH and iota-dopa tests. Thus, only four patients (12%) fulfilled these criteria for cure of GH homeostasis.

Prolactin secretion in the empty sella syndrome, in prolactinomas and in acromegaly

Prolactin (PRL) secretion was studied in 47 patients with empty sella syndrome. Hyperprolactinemia (39-123 micrograms/l) was found in six of them. Intermittent increases in PRL were noted in another seven patients. In most subjects with empty sella syndrome and hyperprolactinemia, diurnal PRL variation was altered or impaired whereas the PRL response to TRH and L-dopa was normal. Low doses of bromocriptine (3.75-5 mg/day) normalized PRL. In patients with prolactinoma and acromegaly who had prolactin levels of 30-165 micrograms/l the diurnal PRL variation and PRL response to TRH were impaired. Patients with prolactinoma failed to suppress PRL during L-dopa test. The dose of bromocriptine required to normalize PRL ranged between 7.5 and 15 mg/day. It is concluded that in subjects with sellar changes and intrasellar cisternal herniation ("empty sella"), and with moderate increases in PRL, the responses to TRH and L-dopa and to bromocriptine may help to differentiate between the empty sella syndrome and a coexisting pituitary tumour.

T4, T3 and reverse-T3 determinations in connection with the TRH test in the evaluation of possible hyperthyroidism

One disadvantage of the TRH test is that an absent or blunted TSH response is seen not only in hyperthyroid patients but also in some normal subjects. The aim of the present study was to elucidate whether the discriminatory power between eu- and hyperthyroidism could be increased by determining the T3 and T4 levels before and after the TRH administration. The study population consists of 30 patients referred for evaluation of suspected hyperthyroidism. The results show that all but one of the patients (n=20) who had T3 levels within the normal reference limits increased these levels after TRH administration, whether their TSH response was normal or blunted. One patient's T3 levels decreased after TRH. All the patients (n=10) who had T3 levels within the hyperthyroid range showed a decrease after TRH. The decrease was significantly correlated (r=0.90) to the magnitude of the increase. No consistent T4 and no change in reverse-T3 response was obtained. The addition of T3, T4 or reverse-T3 determinations in connection with the TRH test does not seem to increase the discriminatory power of the test.

Comparison between serum thyroxine and triiodothyronine estimation and the TRH test in the routine diagnosis of hyperthyroidism

Serum T3 and T4 levels have been determined by a radioimmunoassay technique and the TRH test has been performed in 50 patients in whom hyperthyroidism could not be ruled out by the first clinical examination alone. Each patient was then further evaluated in order to establish the state of the thyroid function. The extent to which the determination of T3 or T4 could replace the TRH test in the routine diagnosis of hyperthyroisism was evaluated. The results showed that 26 of the 50 patients had normal thyroid function and 24 had hyperthyroidism. No patient in the normal groups and all but one in the hyperthyroid group had T3 levels above the upper normal limit (2 S.D.). Two of the patients in the normal group and 19 in the hyperthyroid group had T4 levels above the upper normal limit (2 S.D.). Twenty of the patients in the normal group showed a normal TSH response to TRH (increment is greater than 3.0 micronU/ml); the remaining 6 showed an impaired or absent response. Twenty of the hyperthyroid patients had no response and four had a slightly positive response to TRH. No hyperthyroid patient had a TSH response exceeding 3.0 micronU/ml. It is concluded that the determination of T3 is superior to both the determination of T4 and the TRH test for the laboratory discrimination between eu- and hyperthyroidism.

Serum prolactin and thyrotropin responses to thyrotropin-releasing hormone in men with alcoholic cirrhosis

The serum concentrations of prolactin (PRL) and thyrotropin (TSH) in 12 males with alcoholic cirrhosis during basal condition and after stimulation with thyrotropin-releasing hormone (TRH) were compared with the concentrations in ten thiazide-treated hypertensive and nine normal men. The basal as well as the TRH-stimulated increase in serum PRL was significantly elevated in the cirrhotic males, while the increase in serum TSH was unchanged, compared with hypertensive and normal men. No correlation between clinical or laboratory parameters and serum PRL was found. Serum estradiol was equal in cirrhotic and control subjects and no correlation was found between serum PRL and serum estradiol. These findings favour the concept that raised serum PRL in cirrhotic patients might be caused by a diminished dopaminergic neurotransmission.

Pituitary fuction during X-ray treatment of the hypothalamic-pituitary region as evaluated by the TRH test response

The effect of conventional radiotherapy on the TRH response was studied in fourteen patients, all but one previously surgically treated for pituitary tumors. No change in the TSH response to TRH could be observed either during or after a four week treatment period, thus demonstrating relative resistance of the pituitary gland against irradiation in these patients. We also conclude that the diagnostic value of the TRH test remains unhampered during and in the immediate period after irradiation.

Serum thyroid-stimulating hormone in cerebrovascular disease

A thyrotropin-releasing hormone (TRH) test with serum thyroid-stimulating hormone (TSH) assays was performed in 22 euthyroid stroke patients without thyroid disease and the results were compared with those in 17 age-matched euthyroid controls. Basal and maximum TSH levels after TRH injection were significantly lower in the stroke group without elevation of basal serum thyroid hormone levels. There was a tendency towards an inverse relationship between TSH levels and the degree of pareses of the extremities. The test was repeated in 7 stroke patients 3-4 months after the onset of stroke with essentially the same results. The abnormal TSH parameters in stroke patients seem to be the result of the brain lesion per se.

Symmetrical features in polypeptide hormone-receptor interactions

Symmetrical features were observed in the amino acid sequences of some biologically active peptides. It is suggested that this approximate symmetry is reflected in the conformations of the peptides at their respective biological receptors, and has arisen by natural selection as both peptides and receptors evolved to optimise their mutual fit. It follows that the binding site for each peptide at its receptor would share the same symmetry element. This would arise if the peptide binds to two symmetrically related similar or identical submits in the receptor.

A case of hypothalamic panhypopituitarism with empty sella syndrome: case report and review of the literature

Empty sella syndrome is frequently accompanied with pituitary dysfunction. Most of the patients with empty sella syndrome demonstrate primary pituitary or stalk dysfunction and few cases show hypothalamic dysfunction. A 71-year-old man manifested appetite loss, nausea and vomiting with hyponatremia and adrenal insufficiency. Hormonal evaluation and cranial MRI revealed a panhypopituitarism with empty sella. Intriguingly, while the response of ACTH to CRH administration was exaggerated, the response to insulin hypoglycemia was blunted. Serum PRL levels were normal. Further, decreased level of fT4, slightly elevated basal levels of TSH, and delayed response of TSH to TRH administration were observed. These findings strongly suggest that the panhypopituitarism is caused by hypothalamic dysfunction. The presence of autoantibodies to pituitary and cerebrum in the patient's serum implies an autoimmune mechanism as a pathogenesis.

Mutation of a gene for thyroid transcription factor-1 (TITF1) in a patient with clinical features of resistance to thyrotropin

Resistance to TSH (RTSH [MIM 275200]) is a heterogeneous condition defined by variable degree of insensitivity to biologically active TSH. While this condition is classically caused by loss-of-function mutations of the TSH receptor gene (TSHR), several patients have exhibited RTSH-like phenotype in the apparent absence of TSHR mutations, and some of them have mutations of PAX8 or GNAS1. We identified a Japanese boy with congenital hypothyroidism who suffered from recurrent lower respiratory infection during infancy and choreoathetosis at a later age. At 14 years of age, he was diagnosed as having RTSH, on the basis of compensated hypothyroidism (TSH, 30.2 mU/L; FT4, 1.2 ng/dl), disproportionate increments of thyroid hormones and TSH during a TRH test (DeltaFT3, 0.4 pg/ml; DeltaT3, 13 ng/dl; and DeltaTSH, 88.3 mU/L), and normal ultrasound thyroid image and radioactive iodine uptakes. Molecular analysis for TITF1 revealed a novel de novo heterozygous deletion/insertion mutation (c.470_479delinsGCG,) that is predicted to lose the entire homeodomain and the NK2-specific domain. We suggest that a heterozygous loss-of-function TITF1 mutation can also cause RTSH-compatible phenotype.