Isolated idiopathic central hypothyroidism in an adult, possibly caused by thyrotropin releasing hormone (TRH) deficiency.

Central hypothyroidism (Central H) is mainly due to acquired lesions, either in the pituitary, the hypothalamus or both, and in such cases it is usually associated with deficient secretion of ther pituitary hormones. Isolated central hypothyroidism (I Central H) remains a very rare disease. By the use of the serum thyroid stimulating hormone (TSH) assay as an initial screening test for thyroid disease, the diagnosis of I, Central H can be missed or delayed, since most of these patients have normal or even slightly high serum TSH concentrations. We present a 54-year-old woman with intense tiredness, in whom hypothyroidism was initially and persistently excluded because of normal TSH levels. Further investigations showed again a normal TSH with slightly low free thyroxine (FT4), and Central H was suspected. A thyrotropin releasing hormone (TRH) stimulation test confirmed the diagnosis. No lesion was found by magnetic resonance imaging (MRI). No other pituitary hormone insufficiency was detected. Finally, after excluding, the intake of any drug affecting the hypothalamo-pituitary-thyroid axis and the presence of critical systemic illness, the unusual diagnosis of idiopathic isolated Central H was made. When suspecting Central H, both FT4 and TSH should be measured and if these values are low, TSH response to TRH is recommended to reach specific diagnosis.

Thyrotropin-releasing hormone (TRH) in the cerebellum.

Thyrotropin-releasing hormone (TRH) was originally isolated from the hypothalamus. Besides controlling the secretion of TSH from the anterior pituitary, this tripeptide is widely distributed in the central nervous system and regarded as a neurotransmitter or modulator of neuronal activities in extrahypothalamic regions, including the cerebellum. TRH has an important role in the regulation of energy homeostasis, feeding behavior, thermogenesis, and autonomic regulation. TRH controls energy homeostasis mainly through its hypophysiotropic actions to regulate circulating thyroid hormone levels. Recent investigations have revealed that TRH production is regulated directly at the transcriptional level by leptin, one of the adipocytokines that plays a critical role in feeding and energy expenditure. The improvement of ataxic gait is one of the important pharmacological properties of TRH. In the cerebellum, cyclic GMP has been shown to be involved in the effects of TRH. TRH knockout mice show characteristic phenotypes of tertiary hypothyroidism, but no morphological changes in their cerebellum. Further analysis of TRH-deficient mice revealed that the expression of PFTAIRE protein kinase1 (PFTK1), a cdc2-related kinase, in the cerebellum was induced by TRH through the NO-cGMP pathway. The antiataxic effect of TRH and TRH analogs has been investigated in rolling mouse Nagoya (RMN) or 3-acetylpyridine treated rats, which are regarded as a model of human cerebellar degenerative disease. TRH and TRH analogs are promising clinical therapeutic agents for inducing arousal effects, amelioration of mental depression, and improvement of cerebellar ataxia.

Sarcoidosis: clinical, hormonal, and magnetic resonance imaging (MRI) manifestations of hypothalamic-pituitary disease in 9 patients and review of the literature.

Hypothalamic-pituitary (HP) sarcoidosis has 2 main endocrine manifestations: diabetes insipidus and hyperprolactinemia. We conducted the current study to investigate pituitary dysfunction and perform imaging of the HP area in patients both immediately following diagnosis and after treatment. The study included 6 men and 3 women, with a mean age of 30 years at the onset of sarcoidosis. All patients had both hormonal and magnetic resonance imaging (MRI) HP disorders. All patients had anterior pituitary dysfunction, 7 of them with associated diabetes insipidus. Nine patients had gonadotropin deficiency and 3 had hyperprolactinemia. MRI revealed infundibulum involvement in 5 patients, pituitary stalk thickness abnormality in 5, and involvement of the pituitary gland in 2, associated with other parenchymal brain or spinal cord lesions in 6 patients. All patients had multiple localizations of sarcoidosis, and 5 had histologically confirmed sinonasal localizations. Mean follow-up of the HP disorder was 7.5 years. All patients received prednisone. There was no correlation between the number of hormonal dysfunctions and the area of the HP axis involved as assessed by MRI. Although corticoid treatment was associated with a reduction of radiologic lesions, only 2 patients had partial recovery of hormonal deficiency. In conclusion, hormonal deficiencies associated with HP sarcoidosis frequently include hypogonadism (all patients) and to a lesser degree diabetes insipidus (7 of 9 patients). MRI abnormalities improved or disappeared in 7 cases under corticosteroid treatment, but most endocrine defects were irreversible despite regression of the granulomatous process. Most cases presented with multivisceral localizations and an abnormally high proportion of sinonasal localizations.

Prolactin secretion in mice with thyrotropin-releasing hormone deficiency.

The physiological roles of TRH in pituitary lactotrophs, particularly during lactation, remain unclear. We studied the prolactin (PRL) status, including serum PRL and PRL mRNA levels in the pituitary, in nonlactating and lactating TRH-deficient (TRH(-/-)) mice with a rescue study with thyroid hormone and TRH. We found that, as reported previously for male TRH(-/-) mice, neither the morphology of the lactotrophs, PRL content in the pituitary, nor the serum PRL concentration was changed in nonlactating female TRH(-/-) mice. However, concurrent hypothyroidism induced a mild decrease in the PRL mRNA level. In contrast, during lactation, the serum PRL level in TRH(-/-) mice was significantly reduced to about 60% of the level in wild-type mice, and this was reversed by prolonged TRH administration, but not by thyroid hormone replacement. The PRL content and PRL mRNA level in the mutant pituitary during lactation were significantly lower than those in wild-type mice, and these reductions were reversed completely by TRH administration, but only partially by thyroid hormone replacement. Despite the low PRL levels, TRH(-/-) dams were fertile, and the nourished pups exhibited normal growth. Furthermore, the morphology of the pituitary was normal, and high performance gel filtration chromatography analysis of the PRL molecule revealed no apparent changes. We concluded that 1) TRH is not essential for pregnancy and lactation, but is required for full function of the lactotrophs, particularly during lactation; and 2) the PRL mRNA level in the pituitary is regulated by TRH, both directly and indirectly via thyroid hormone.

Deletion of the Nhlh2 transcription factor decreases the levels of the anorexigenic peptides alpha melanocyte-stimulating hormone and thyrotropin-releasing hormone and implicates prohormone convertases I and II in obesity.

Body weight is controlled by the activation of signal transduction pathways in both the brain and peripheral tissues. Interestingly, although many hypothalamic neuropeptides and receptors have been implicated in the regulation of body weight, the transcriptional and posttranscriptional mechanisms through which these genes are expressed in response to changes in energy balance remain unclear. Our laboratory studies a mouse in which targeted deletion of the neuronal basic helix-loop-helix (bHLH) transcription factor, nescient helix-loop-helix 2 protein (Nhlh2), results in adult-onset obesity. The aim of this work was to use the phenotype of the Nhlh2 knockout mouse and the expression pattern of Nhlh2 to identify genes that are regulated by this transcription factor. In this article, we show that Nhlh2 is expressed throughout the adult hypothalamus. Using dual-label in situ hybridization, we demonstrate that, in the arcuate nucleus of the adult hypothalamus (ARC), Nhlh2 expression can be found in rostral proopiomelanocortin (POMC) neurons, whereas in the paraventricular nucleus (PVN), Nhlh2 is expressed in TRH neurons. In addition, we find that hypothalamic POMC-derived alphaMSH in the ARC and TRH in the PVN are regulated posttranscriptionally via Nhlh2-mediated control of prohormone convertase I and II mRNA levels. This is the first report in which regulation of body weight is linked to the action of a neuronal bHLH transcription factor on prohormone convertase mRNA levels. Furthermore, this work supports a direct role for transcriptional control of neuropeptide processing enzymes in the etiology of adult-onset obesity.

Mice lacking the thyrotropin-releasing hormone gene: what do they tell us?

Thyrotropin-releasing hormone (TRH) is localized in the brain hypothalamus and stimulates the secretion and synthesis of pituitary thyrotropin (TSH). Although TRH deficiency caused by artificial hypothalamic destructions has been reported to result in significant decreases in TSH secretion in rodents, clinical observations from the patients with possible TRH deficiency did not entirely agree with these animal results. Because of its ubiquitous distribution throughout the brain and in the peripheral tissues, TRH has been suggested to possess a wide variety of functions in these regions. However, the neurobehavioral and peripheral actions of TRH still remains to be established. It has been, therefore, anticipated that detailed analysis of TRH-knockout mice might provide insight into the physiological significance of endogenous TRH. The present review focuses on the phenotypic findings of mice deficient in TRH.

A novel TRH-PFTAIRE protein kinase 1 pathway in the cerebellum: subtractive hybridization analysis of TRH-deficient mice.

TRH has been reported to possess several neurophysiological actions in the brain. To gain insights into the molecular mechanisms underlying these effects, particularly in the cerebellum, we attempted to clone a cDNA that was regulated by TRH using TRH knockout mice and subtractive cDNA analysis. Over 100 clones obtained by subtractive hybridization analysis between the wild-type and TRH-1-cerebellum were analyzed. Four clones among them were identical and cdc2-related kinase (PFTAIRE protein kinase 1 (PFTK1)) cDNA, which was previously reported to be expressed only in the brain and testis. PFTK1 mRNA levels in the euthyroid TRH-1- cerebellum supplemented with thyroid hormone were significantly decreased compared with those in the wild-type. Induction of PFTK1 mRNA by TRH was also observed in a time- and dose-dependent manner in human medulloblastoma-derived HTB-185 cells that expressed TRH receptor subtype I mRNA. In addition, treatment of 8-Br-cGMP significantly increased PFTK1 mRNA levels, and a specific inhibitor of cGMP production, ODQ, completely blocked TRH-induced expression of PFTK1 mRNA. Furthermore, induction of PFrK1 mRNA by TRH was significantly inhibited by a NOS specific inhibitor, L-NAME, but not by a MEK inhibitor, PD98059 or a calcium channel inhibitor, nimodipine. These findings demonstrated, for the first time, a novel pathway between a neuropeptide and a cell cycle related peptide in the brain, and PFTK1 may be a key regulator for TRH action in t he cerebellum through t he NO-cGMP pathway.

Abundance of cyclo (His-Pro)-like immunoreactivity in the brain of TRH-deficient mice.

Cyclo(His-Pro) or CHP was initially discovered as a metabolite of thyrotropin-releasing hormone (TRH) resulting from the action of the enzyme Pyroglutamyl aminopeptidase. Physiologic and pharmacologic studies that followed this initial discovery provided indirect evidence that all CHP may not be derived from TRH. However, the recent availability of a TRH-deficient mouse has made it possible to reinvestigate whether CHP is derived from TRH. In the present study, we examined distribution of CHP and TRH in TRH-deficient mice. Northern blot analysis confirmed the absence of preproTRH mRNA in both the hypothalamus and the cortex of TRH-deficient mice. Brains from the wild-type and TRH-deficient mice were dissected into 7 regions, and TRH and CHP concentrations were determined by specific radioimmunoassay (RIA) in each region. Whereas TRH was identified in all regions of the wild-type brain, with the highest concentration in the hypothalamus, no detectable TRH was observed in any region in the TRH-deficient mice. While CHP-like immunoreactivity (CHP-LI) was present in all regions in the wild-type brain, its concentration was reduced by approximately 50% in the hypothalamus and cerebral cortex of TRH-deficient mice, with no change in other brain regions. Furthermore, the CHP-LI present in the brain of TRH-deficient mice was immunologically and chromatographically identical to synthetic CHP. These findings strongly suggest that a portion of the CHP in the brain is derived from sources other than TRH.

Tertiary hypothyroidism and hyperglycemia in mice with targeted disruption of the thyrotropin-releasing hormone gene.

Thyrotropin-releasing hormone (TRH) is a brain hypothalamic hormone that regulates thyrotropin (TSH) secretion from the anterior pituitary and is ubiquitously distributed throughout the brain and other tissues including pancreas. To facilitate studies into the role of endogenous TRH, we have used homologous recombination to generate mice that lack TRH. These TRH-/- mice are viable, fertile, and exhibit normal development. However, they showed obvious hypothyroidism with characteristic elevation of serum TSH level and diminished TSH biological activity. Their anterior pituitaries exhibited an apparent decrease in TSH immunopositive cells that was not due to hypothyroidism. Furthermore, this decrease could be reversed by TRH, but not thyroid hormone replacement, suggesting a direct involvement of TRH in the regulation of thyrotrophs. The TRH-/- mice also exhibited hyperglycemia, which was accompanied by impaired insulin secretion in response to glucose. These findings indicate that TRH-/- mice provide a model of exploiting tertiary hypothyroidism, and that TRH gene abnormalities cause disturbance of insulin secretion resulting in marked hyperglycemia.

Central hypothyroidism due to isolated TRH deficiency in a depressive man.

A depressive man was evaluated for developing chronic fatigue and cold intolerance, in whom laboratory findings showed decreased thyroid hormone levels (T4, 2.7 micrograms dl-1; T3, 0.76 ng ml-1) with normal blood levels of TSH. A single bolus injection of TRH (500 micrograms) significantly stimulated prolactin secretion, but did not cause an increase in blood TSH levels (basal level, 1.2 microU ml-1 vs. 1.3 microU ml-1 30 min after injection). By contrast, TRH-induced TSH stimulation occurred after repeated injection of TRH for 4 consecutive days (basal level, 1.5 microU ml-1 vs. 5.6 microU ml-1 30 min after injection). Blood thyroid hormone concentrations were restored to normal levels after long-term administration of TRH. Other pituitary functions remained unchanged. A diagnosis of central hypothyroidism due to isolated TRH deficiency was made in this case, and the data presented here indicate that partial resistance of pituitary thyrotrophs to TRH may be associated with depression.

Spinal cord TRH deficiency is associated with incomplete recovery of denervated muscle in the rat.

The raphe-spinal pathway, which contains co-localized serotonin (5-HT), thyrotropin-releasing hormone (TRH), and several TRH-prohormone-derived non-TRH peptides, projects to the ventral horn of the spinal cord. Pharmacologic ablation of this pathway with the 5-HT neurotoxin, 5,7-dihydroxytryptamine, in neonatal rats resulted in deficient recovery of plantar foot muscles, functionally denervated with botulinum toxin type A. Failure of reinnervation was suggested by slower and incomplete recovery of the plantar foot compound muscle action potential amplitude and by a reduced mean diameter of plantar foot muscle fibers in ablated rats. These findings indicate that deprivation of alpha motor neurons from descending raphe-spinal input interferes with their ability to respond to muscle-derived signals for reinnervation.

Primary idiopathic hypothalamic hypothyroidism. Report of four cases.

One man and three women with hypothalamic hypothyroidism are described; they had isolated thyrotropin-releasing hormone deficiency, otherwise normal pituitary function, and no identifiable central nervous system anatomic abnormality. Serum thyrotropin levels were low and thyrotropic response to thyrotropin-releasing hormone was uniformly present, consistent with a hypothalamic cause of hypothyroidism. In two patients, hypothyroidism was transient and spontaneously resolved; in one of them, it was recurrent. Because hypothalamic hypothyroidism is mild and potentially reversible, it is suggested that such patients have follow-up evaluation before therapy is initiated in order to avoid unnecessary treatment.

Growth hormone deficiency in adults--an indication for therapy?

Case studies are presented for two patients, one with isolated hGH deficiency and one with multiple hormone deficiencies. The patients were studied 3 months before, and 3 and 9 months after discontinuing hGH therapy, at 19 and 18 years of age, respectively. Strength in the quadriceps femoris, cross-sectional area of the quadriceps muscles and cross-sectional muscle fibre area were measured. In the patient with multiple hormone deficiencies, clear decreases in all three parameters were evident after discontinuing hGH treatment. There were no significant changes in the other patient. Reasons for these differences are discussed.

Hypothalamic hypothyroidism due to isolated thyrotropin-releasing hormone (TRH) deficiency.

Cold intolerance and secondary amenorrhea developed in a patient who had meningoencephalitis 4 yr prior to study. A clinical diagnosis of hypothalamic hypothyroidism was made on the basis of low serum thyroxine and triiodothyronine levels, and low plasma thyrotropin concentrations, which were responsive to thyrotropin-releasing hormone (TRH). The secretion of the remaining pituitary hormones (growth hormone, prolactin, adrenocorticotropin and gonadotropins) was intact. Not only was thyroid function normalized by oral administration of TRH, but also menses resumed after adequate replacement therapy with thyroid hormone. These results imply that hypothyroidism in this patient was due to isolated dysfunction of hypothalamic TRH release.