Thyroid hormone action on ACTH secretion

Evaluation of Neuro-Hormonal Dynamics after the Administration of Probiotic Microbial Strains in a Murine Model of Hyperthyroidism

The microbiota-gut-brain axis has received increasing attention in recent years through its bidirectional communication system, governed by the ability of gut microorganisms to generate and regulate a wide range of neurotransmitters in the host body. In this research, we delve into the intricate area of microbial endocrinology by exploring the dynamic oscillations in neurotransmitter levels within plasma and brain samples. Our experimental model involved inducing hyperthyroidism in mice after a "probiotic load" timeframe using two strains of probiotics (Lactobacillus acidophilus, Saccharomyces boulardii, and their combination). These probiotic interventions continued throughout the experiment and were intended to uncover potential modulatory effects on neurotransmitter levels and discern if certain probiotic strains exhibit any protection from hyperthyroidism. Moreover, we aimed to outline the eventual connections between the gut microbiota and the hypothalamus-pituitary-thyroid axis. As our study reveals, there are significant fluctuations in crucial neurotransmitters within the hyperthyroidism model, related to the specific probiotic strain or combination. These findings could support future therapeutic approaches, help healthcare professionals choose between different probiotic therapies, and also allow us proceed with caution when administering such treatments, depending on the health status of hyperthyroid patients.

Perspective: Drawing on Findings From Critical Illness to Explain Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

We propose an initial explanation for how myalgic encephalomyelitis / chronic fatigue syndrome (ME/CFS) could originate and perpetuate by drawing on findings from critical illness research. Specifically, we combine emerging findings regarding (a) hypoperfusion and endotheliopathy, and (b) intestinal injury in these illnesses with our previously published hypothesis about the role of (c) pituitary suppression, and (d) low thyroid hormone function associated with redox imbalance in ME/CFS. Moreover, we describe interlinkages between these pathophysiological mechanisms as well as “vicious cycles” involving cytokines and inflammation that may contribute to explain the chronic nature of these illnesses. This paper summarizes and expands on our previous publications about the relevance of findings from critical illness for ME/CFS. New knowledge on diagnostics, prognostics and treatment strategies could be gained through active collaboration between critical illness and ME/CFS researchers, which could lead to improved outcomes for both conditions.

Theory: Treatments for Prolonged ICU Patients May Provide New Therapeutic Avenues for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

We here provide an overview of treatment trials for prolonged intensive care unit (ICU) patients and theorize about their relevance for potential treatment of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Specifically, these treatment trials generally target: (a) the correction of suppressed endocrine axes, notably through a "reactivation" of the pituitary gland's pulsatile secretion of tropic hormones, or (b) the interruption of the "vicious circle" between inflammation, oxidative and nitrosative stress (O&NS), and low thyroid hormone function. There are significant parallels in the treatment trials for prolonged critical illness and ME/CFS; this is consistent with the hypothesis of an overlap in the mechanisms that prevent recovery in both conditions. Early successes in the simultaneous reactivation of pulsatile pituitary secretions in ICU patients-and the resulting positive metabolic effects-could indicate an avenue for treating ME/CFS. The therapeutic effects of thyroid hormones-including in mitigating O&NS and inflammation and in stimulating the adreno-cortical axis-also merit further studies. Collaborative research projects should further investigate the lessons from treatment trials for prolonged critical illness for solving ME/CFS.

Hypothesis: Mechanisms That Prevent Recovery in Prolonged ICU Patients Also Underlie Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)

Here the hypothesis is advanced that maladaptive mechanisms that prevent recovery in some intensive care unit (ICU) patients may also underlie Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Specifically, these mechanisms are: (a) suppression of the pituitary gland's pulsatile secretion of tropic hormones, and (b) a "vicious circle" between inflammation, oxidative and nitrosative stress (O&NS), and low thyroid hormone function. This hypothesis should be investigated through collaborative research projects.

Maternal predator odour exposure programs metabolic responses in adult offspring

A cardinal feature of the reaction to stress is the promotion of energy mobilization, enabling appropriate behavioural responses. Predator odours are naturalistic and ecologically relevant stressors present over evolutionary timescales. In this study, we asked whether maternal predator odour exposure could program long-term energy mobilization in C57BL/6 mice offspring. To test this hypothesis, we measured rates of oxygen consumption in prenatally predator odour exposed mice in adulthood while controlling for levels of locomotor activity at baseline and under stress. Circulating thyroid hormone levels and the transcript abundance of key regulators of the hypothalamic-pituitary-thyroid axis within the periventricular nucleus (PVN) of the hypothalamus and in the liver, including carriers and receptors and thyrotropin-releasing hormone, were measured as endocrine mediators facilitating energy availability. Prenatally predator odour exposed mice of both sexes mobilized more energy during lower energy demand periods of the day and under stressful conditions. Further, prenatally predator odour exposed mice displayed modifications of their hypothalamic-pituitary-thyroid axis through increased circulating thyroxine and thyroid hormone receptor α within the PVN and decreased transthyretin in the liver. Overall, these results suggest that maternal exposure to predator odour is sufficient to increase long-term energy mobilization in adult offspring.

Modulation of central glucocorticoid receptors in short- and long-term experimental hyperthyroidism

Hyperthyroidism is associated with a significant increase in circulating glucocorticoid levels and hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. The aim of this study was to examine whether the HPA axis hyperactivity observed in hyperthyroidism may be explained by a disturbed feedback inhibition of endogenous glucocorticoids through two specific intracellular receptors in the brain: the high affinity mineralocorticoid receptor (MR) and the lower affinity glucocorticoid receptor (GR). Cytosolic receptor binding and gene expression was assessed in rats with short (7 days) and long standing (60 days) eu- and hyperthyroidism. Glucocorticoid receptor number and binding affinity (Kd) in the hippocampus were measured using [(3)H2]-dexamethasone radioreceptor assay. In situ hybridization was employed to examine the effects of hyperthyroidism on the GR and MR mRNA levels in the hippocampus and the pituitary. Both short- and long-term hyperthyroid rats showed pronounced reduction in the concentration of cytosolic GR in the hippocampus, without changes in binding affinity or changes in GR expression. In contrast, GR mRNA in the pituitary increased after 7 days and decreased after 60 days of thyroxin treatment. MR mRNA was moderately affected. Hyperthyroidism is associated with significant decreases in hippocampal GR levels supporting the hypothesis that hyperactivity of the HPA axis observed in experimentally induced hyperthyroidism may be attributed, at least in part, to decreased negative feedback at the level of the hippocampus. These findings further support the notion that a central locus is principally responsible for the hyperactivity of the HPA axis observed in hyperthyroidism.

Adrenal function in cats with hyperthyroidism

Adrenal function may be altered in animals with hyperthyroidism. The aim of the study was to assess adrenal function of hyperthyroid cats (n = 17) compared to healthy cats (n = 18) and cats with chronic diseases (n = 18). Adrenal function was evaluated by adrenocorticotropic hormone (ACTH) stimulation test and the urinary cortisol to creatinine ratio (UCCR) was determined. Length and width of both adrenal glands were measured via ultrasound. Hyperthyroid cats had significantly higher cortisol levels before and after stimulation with ACTH than the other groups. However, the UCCR was not elevated in hyperthyroid cats. The size of the adrenal glands of hyperthyroid cats was not significantly different from the size of those of healthy cats. The results indicate that cats with hyperthyroidism have a higher cortisol secretory capacity in a hospital setting. The normal size of the adrenal glands suggests that cortisol levels may not be increased permanently.

Adult-onset hypothyroidism enhances fear memory and upregulates mineralocorticoid and glucocorticoid receptors in the amygdala

Hypothyroidism is the most common hormonal disease in adults, which is frequently accompanied by learning and memory impairments and emotional disorders. However, the deleterious effects of thyroid hormones deficiency on emotional memory are poorly understood and often underestimated. To evaluate the consequences of hypothyroidism on emotional learning and memory, we have performed a classical Pavlovian fear conditioning paradigm in euthyroid and adult-thyroidectomized Wistar rats. In this experimental model, learning acquisition was not impaired, fear memory was enhanced, memory extinction was delayed and spontaneous recovery of fear memory was exacerbated in hypothyroid rats. The potentiation of emotional memory under hypothyroidism was associated with an increase of corticosterone release after fear conditioning and with higher expression of glucocorticoid and mineralocorticoid receptors in the lateral and basolateral nuclei of the amygdala, nuclei that are critically involved in the circuitry of fear memory. Our results demonstrate for the first time that adult-onset hypothyroidism potentiates fear memory and also increases vulnerability to develop emotional memories. Furthermore, our findings suggest that enhanced corticosterone signaling in the amygdala is involved in the pathophysiological mechanisms of fear memory potentiation. Therefore, we recommend evaluating whether inappropriate regulation of fear in patients with post-traumatic stress and other mental disorders is associated with abnormal levels of thyroid hormones, especially those patients refractory to treatment.

Iodothyronine deiodinases and cancer

Thyroid hormones (TH) regulate key cellular processes, including proliferation, differentiation, and apoptosis in virtually all human cells. Disturbances in TH pathway and the resulting deregulation of these processes have been linked with neoplasia. The concentrations of TH in peripheral tissues are regulated via the activity of iodothyronine deiodinases. There are 3 types of these enzymes: type 1 and type 2 deiodinases are involved in TH activation while type 3 deiodinase inactivates TH. Expression and activity of iodothyronine deiodinases are disturbed in different types of neoplasia. According to the limited number of studies in cancer cell lines and mouse models changes in intratumoral and extratumoral T3 concentrations may influence proliferation rate and metastatic progression. Recent findings showing that increased expression of type 3 deiodinases may lead to enhanced tumoral proliferation support the idea that deiodinating enzymes have the potential to influence cancer progression. This review summarizes the observations of impaired expression and activity in different cancer types, published to date, and the mechanisms behind these alterations, including impaired regulation via TH receptors, transforming growth factor-β, and Sonic-hedgehog pathway. Possible roles of deiodinases as cancer markers and potential modulators of tumor progression are also discussed.

Effects of competitive and noncompetitive showjumping on total and free iodothyronines, β-endorphin, ACTH and cortisol levels of horses

REASONS FOR PERFORMING STUDY

Limited knowledge exists about the differentiated effects of competitive and noncompetitive showjumping on thyroid function and relationships with hypothalamic-hypophysis-corticoadrenal hormones.

OBJECTIVES

To obtain preliminary data about differentiated effects of competitive and noncompetitive showjumping on total and free iodothyronines, β-endorphin, ACTH and cortisol of horses.

MATERIAL AND METHODS

Five trained healthy jumper horses were studied during competitive and noncompetitive showjumping, performed in the same circuit design over 10 fences of 1.10 m. Hormone levels before, 5 and 30 min post exercise were recorded. Serum iodothyronines and cortisol concentrations were measured in duplicate utilising EIA kits. Serum ACTH and plasma β-endorphin concentrations were analysed in duplicate utilising RIA kits. Two-way RM ANOVA was applied to test for effects of interaction between different type of session and time. Significant differences between post exercise and basal values were established using Bonferroni's multiple comparison test. A linear correlation analysis (Pearson's method) was performed to analyse the relationships between total and free iodothyronines and between iodothyronines and β-endorphin, ACTH and cortisol.

RESULTS

In sampling times adopted no statistical different effects of type of session were recorded on hormone variables. Sampling time affected ACTH (F = 4.25; P < 0.02) and T(4) (F = 4.43; P < 0.02) post exercise changes. During the noncompetitive session, significant correlations existed between T(4) and β-endorphin (r = -0.56), ACTH (r = -0.65), between β-endorphin and ACTH (r = 0.52) and between T(3) and fT(3) (r = 0.72); during competition between β-endorphin and T(3) (r = -0.67), fT(3) (r = -0.59).

CONCLUSIONS

These preliminary results could demonstrate correlations between thyroid hormones and β-endorphin response to showjumping, although no definitive conclusion can be produced concerning the relationships between HPA and thyroid function during exercise.

Effects of thyroid status on arginine vasotocin receptor VT2R expression and adrenal function in osmotically stimulated domestic fowl

The role of thyroid hormones in the regulation of adrenal function during stress has been documented in mammals, but only limited reports are available in avian species. The present study was undertaken to analyze the effect of hyper- or hypothyroidism on the adrenal activity under control (hydrated) and osmotically stressed (water deprived, WD) conditions, with special emphasis on the expression of arginine vasotocin receptor VT2 (VT2R) in pituitary corticotrophs. Chickens were made hyper- or hypothyroidic by injecting thyroxine (T4) and 2-thiouracil (TU), respectively for 14 days. After 10 days of injections, one sub-group of both, T4- or TU-treated chickens were subjected to osmotic stress by water deprivation. Hyperthyroidism stimulated adrenal steroidogenic activity compared to euthyroid control birds, but no change was observed in the expression of VT2R. On the other hand, TU-induced hypothyroidism however showed no effect on adrenal gland, but a significant increase in the expression of VT2R was observed. Neither hyper- nor hypothyroidism altered pro-opiomelanocortin (POMC) mRNA levels. Following osmotic stress, no effect was observed either on the adrenal gland or on the VT2R expression in hyperthyroidic birds, but in hypothyroidic birds, osmotic stress stimulated adrenal steroidogenic activity and decreased VT2R expression in comparison to its respective controls (T4 or TU). Expression of POMC mRNA was again unaltered following osmotic stress. Although exact mechanism is not clear, the data indicate that high plasma T4 level stimulates adrenal activity and may also modulate function of the pituitary-adrenal axis during dehydration.

Experimentally-induced hyperthyroidism is associated with activation of the rat hypothalamic-pituitary-adrenal axis

OBJECTIVE

Previous studies on the effects of altered thyroid function on the secretion and metabolism of adrenocortical hormones suggest a degree of adrenocortical hyperactivity in hyperthyroidism. We have previously shown that experimentally-induced hyperthyroidism is associated with significant alterations in pituitary-adrenal responsiveness to synthetic ovine corticotropin-releasing hormone (oCRH) that are contingent upon the duration of the altered thyroid function. The purpose of this study was to assess the time-dependent effects of hyperthyroidism on the functional integrity of the hypothalamic-pituitary-adrenal (HPA) axis by in vivo stimulation of the hypothalamic CRH neuron and adrenal cortex.

METHODS

The functional integrity of the HPA axis was examined in vivo in sham-thyroidectomized male Sprague-Dawley rats given placebo or in thyroidectomized rats given 50 mug of thyroxine every day for 7 or 60 days. Responses to insulin-induced hypoglycemia and IL-1alpha stimulation were used to assess the hypothalamic CRH neuron. Adrenocortical reserve was assessed in response to low-dose adrenocorticotropic hormone (ACTH), following suppression of the HPA axis with dexamethasone. Adrenal and thymus tissue weight, in addition to basal plasma ACTH, corticosterone and thyroid indices were also determined.

RESULTS

Basal plasma corticosterone and corticosterone binding globulin (CBG) concentrations were significantly increased in short- and long-term hyperthyroid rats, and by 60 days, cerebrospinal fluid (CSF) corticosterone levels were significantly increased. Basal plasma ACTH levels were similar to controls. Although plasma ACTH responses to hypoglycemic stress and IL-1alpha administration in both short- and long-term hyperthyroidism were normal, corticosterone responses to the ACTH release during the administration of these stimuli were significantly increased. The adrenal reserve was significantly elevated in short-term hyperthyroidsim. Long-term hyperthyroidism, however, was associated with a significant reduction in adrenocortical reserve. A significant increase in adrenal weights and a decrease in thymus weights were observed in both short- and long-term hyperthyroidism.

CONCLUSIONS

The available data confirms that hyperthyroidism is associated with hypercorticosteronemia, although the locus that is principally affected still remains unclear. Despite the sustained hyperactivity of the HPA axis, long-term experimentally-induced hyperthyroidism is associated with diminished adrenal functional reserve. The alterations in HPA function in states of disturbed thyroid function were found to be somewhat more pronounced as the duration of thyroid dysfunction increased.

Effect of Duration of Cold Stress on Plasma Adrenal and Thyroid Hormone Levels and Immune Responses in Chicken Lines Divergently Selected for Antibody Responses

There is increasing evidence that stress affects various immune processes. Some of these changes are due to hormonal changes involving corticosterone (CORT), triiodothyronine (T3), and thyroxine (T4). Effects of stress depend on the nature of specific stressors (e.g., thermal extremes, diet, pollutants), and stress-modifiers (e.g., genetic make-up, duration and severity of the stressors). We studied the effects of a specific stress (cold stress) with stress-modifiers (duration of stress and genotype of the bird) on immune responses and plasma adrenal and thyroid hormone levels in 3 layer-type chicken lines. Two lines were divergently selected for high (H line) or low (L line) antibody responses to SRBC, and the third line was a randombred control (C) line. Growing chicks (3- to 4-wk-old) of the 3 lines were feed-restricted at 80% of ad libitum consumption, and subjected to cold stress (CS) at 10 degrees C continuously for 7, 5, 3, 1, or 0 d before immunization with keyhole limpet hemocyanin (KLH). Specific antibody titers to KLH, and in vitro lymphocyte proliferation (LP) upon mitogen stimulation were measured. In addition, adrenal and thyroid hormone levels were measured in the plasma samples collected at the end of CS. No significant effect of duration of CS on specific antibody titers was found in the 3 lines. A significant enhancing effect of CS was found on LP. A significant dose-dependent suppressive effect of CS was found on plasma CORT levels. One day of CS had a significant enhancing effect on T3 levels. There was no significant effect of duration of CS on T4 levels. We conclude that CS does not affect specific antibody responses, but may have a modulating effect on cellular immunity and plasma CORT levels, depending on the duration of the stress. The present study suggests an inverse relationship between LP and CORT. This is the first study that reveals an absence of significant differences in adrenal and thyroid hormone levels in the described selection lines.

Dysregulation of iodothyronine deiodinase enzyme expression and function in human pituitary tumours

OBJECTIVE

Thyroid hormones (THs) perform essential roles in pituitary function. They regulate anterior pituitary hormone secretion and are also key determinants of pituitary cell proliferation and differentiation. The critical role of deiodinase enzymes, which serve as prereceptor regulators of TH action, remains largely unexplored. Three deiodinase enzymes metabolize active and inactive THs and thereby determine tissue concentrations of the biologically active ligand, tri-iodothyronine (T3). We hypothesized that aberrant expression of deiodinase enzymes and/or altered enzyme activity in pituitary tumours may change tissue concentrations of THs and influence their growth and secretory characteristics.

STUDY DESIGN AND PATIENTS

We studied 105 pituitary tumours and 10 normal pituitaries for expression of deiodinase enzyme mRNAs encoding types 1 (D1), 2 (D2) and 3 (D3) using real-time RT-PCR. Enzyme activity data from 20 pituitary samples were also obtained.

RESULTS

Pituitary tumours expressed significantly increased D3 mRNA (6.5-fold, P < 0.0005) compared with normal pituitaries. D2 mRNA was also increased 2.6-fold (P = 0.005) in pituitary tumours compared with normals. The rare TSH-secreting pituitary tumour subtype expressed a 13.1-fold excess of D3 mRNA and reduced D2 mRNA (0.1-fold of normal pituitaries). D2 mRNA expression in ACTH-secreting tumours was similarly reduced to 0.1-fold that in normal pituitaries.

CONCLUSIONS

Pituitary adenomas express abnormal levels of deiodinase enzymes compared to normal pituitaries. These abnormalities may have functional consequences on pituitary tumour growth. In the case of TSH-secreting pituitary adenomas, the observed pattern of deiodinase mRNA expression may explain the 'resistance' of this tumour type to TH feedback.

Effects of chronic mild stress on lymphocyte proliferative response. Participation of serum thyroid hormones and corticosterone

There is increasing evidence that stress produces changes in various immune processes. Some of these changes may be due to neurochemical and hormonal alterations including thyroid hormones levels. This work was carried out to study the impact of chronic mild stress (CMS) exposure on proliferative responses and its correlation with serum thyroid hormone levels. In addition, the influence of serum corticosterone levels on these responses was also studied. For this purpose, mice were submitted from1 to 6 weeks to a CMS model. After undergoing the stress schedule for 4 weeks, an alteration in the proliferative response was observed. Lymphocytes from exposed animals showed a decrease in T-cell response to concanavalin-A (Con A) and phytohemagglutinin (PHA) and an increase in B-cell proliferation to lipopolysaccharides (LPS). In parallel, a reduction in T3 and T4 serum levels was observed. On the contrary, serum corticosterone levels increased in animals exposed to CMS for 1 or 2 weeks and then return to normal values. Lowering serum thyroid hormone levels by propylthiouracil (PTU) treatment negatively modulates T-cell response without affecting B-cell response. On the other hand, the substitutive T4 treatment in stressed animals improved significantly the proliferative T-cell response. Non-significative changes in CD4/CD8 ratio were observed neither in stressed, PTU- or T4-treated animals. Taken together, our results suggest an impact of chronic stress on thyroid function that in turn alters T-cell response. These findings may help to elucidate the physiological mechanisms through which stress plays a roll in the etiology of many diseases.

Thyroxine modulates corticotropin-releasing factor but not arginine vasopressin gene expression in the hypothalamic paraventricular nucleus of the developing Rat

Neonatal rats were daily injected with 100 microg/kg T4 and killed at 4, 8 or 15 days. Circulating corticosterone and corticosteroid binding globulin concentrations increased in 8- and 15-day-old rats after T4 treatment. Plasma adrenocorticotropic hormone (ACTH) concentrations, pituitary ACTH content and pro-opiomelanocortin mRNA expression were unaffected in T4-treated rats. T4 treatment induced an increase in corticotropin-releasing factor (CRF) mRNA expression in the whole population of CRF synthesizing cells of the paraventricular nucleus (PVN) that became significant at day 8 and disappeared at day 15. Double labelling in situ hybridization revealed that CRF gene expression in the CRF+/arginine vasopressin (AVP)+ subpopulation was increased at days 4 and 8 and decreased at day 15. CRF immunoreactivity in the zona externa of the median eminence increased with age but was not affected by the experimental hyperthyroidism. The degree of CRF and AVP colocalization, the concentration of AVP mRNA in the parvo and magnocellular cell bodies of the PVN and the density of immunoreactive AVP in the zona interna or zona externa of the median eminence did not change after T4 treatment. Our data demonstrate that experimental hyperthyroidism accelerates the maturation of hypothalamic CRF gene expression, including in particular in the CRF+/AVP+ subpopulation, during the stress hyporesponsive period. These observations suggest that the physiological peak of plasma thyroxine that occurs between days 8-12 may participate in the maturation of hypothalamic CRF cells.

Changes in immune parameters seen in Gulf War veterans but not in civilians with chronic fatigue syndrome

The purpose of this study was to evaluate immune function through the assessment of lymphocyte subpopulations (total T cells, major histocompatibility complex [MHC] I- and II-restricted T cells, B cells, NK cells, MHC II-restricted T-cell-derived naive and memory cells, and several MHC I-restricted T-cell activation markers) and the measurement of cytokine gene expression (interleukin 2 [IL-2], IL-4, IL-6, IL-10, IL-12, gamma interferon [IFN-gamma], and tumor necrosis factor alpha [TNF-alpha]) from peripheral blood lymphocytes. Subjects included two groups of patients meeting published case definitions for chronic fatigue syndrome (CFS)-a group of veterans who developed their illness following their return home from participating in the Gulf War and a group of nonveterans who developed the illness sporadically. Case control comparison groups were comprised of healthy Gulf War veterans and nonveterans, respectively. We found no significant difference for any of the immune variables in the nonveteran population. In contrast, veterans with CFS had significantly more total T cells and MHC II+ T cells and a significantly higher percentage of these lymphocyte subpopulations, as well as a significantly lower percentage of NK cells, than the respective controls. In addition, veterans with CFS had significantly higher levels of IL-2, IL-10, IFN-gamma, and TNF-alpha than the controls. These data do not support the hypothesis of immune dysfunction in the genesis of CFS for sporadic cases of CFS but do suggest that service in the Persian Gulf is associated with an altered immune status in veterans who returned with severe fatiguing illness.

A novel endogenous corticotropin release inhibiting factor

ACTH is the major regulator of the body's adaptive response to stress and the physiological stimulus for glucocorticoid secretion. A hypothalamic corticotropin release inhibiting factor (CRIF) that inhibits ACTH synthesis and secretion has long been postulated but was not characterized until recently. We have recently identified a 22 amino acid peptide, prepro-thyrotropin releasing hormone (TRH) 178-199 that inhibits basal and stimulated ACTH synthesis and secretion in vitro and stress-induced ACTH secretion in vivo. Prepro-TRH 178-199 is abundant in several brain regions, including the external zone of the median eminence, where its concentration changes in response to stress. We propose that this peptide is a physiological regulator of ACTH production: an endogenous CRIF. Because prepro-TRH 178-199 is encoded within the same precursor as TRH, its expression is likely to be negatively regulated by thyroid hormones leading to changes in endogenous glucocorticoid levels. Streptococcal cell wall (SCW)-induced inflammation, a model of rheumatoid arthritis (RA), was alleviated after long-term thyroxine treatment. Inversely, a hypothyroid milieu led to decreased basal hypothalamic-pituitary-adrenal activity, but increased expression of IL-1 beta and MIP-1 alpha, specific markers for RA in humans. These results suggest that this putative CRIF may be an important component in the development of RA and that regulation of prepro TRH may be highly relevant to the development of other autoimmune diseases that are also exacerbated by low endogenous glucocorticoid levels.

Acute effects of thyroid hormones on the production of adrenal cAMP and corticosterone in male rats

The acute effects of thyroid hormones on glucocorticoid secretion were studied. Venous blood samples were collected from male rats after they received intravenous 3,5,3'-triiodothyronine (T3) or thyroxine (T4). Zona fasciculata-reticularis (ZFR) cells were treated with adrenocorticotropic hormone (ACTH), T3, T4, ACTH plus T3, or ACTH plus T4 at 37 degrees C for 2 h. Corticosterone concentrations in plasma and cell media, and also adenosine 3',5'-cyclic monophosphate (cAMP) production in ZFR cells in the presence of 3-isobutyl-1-methylxanthine, were determined. The effects of thyroid hormones on the activities of steroidogenic enzymes of ZFR cells were measured by the amounts of intermediate steroidal products separated by thin-layer chromatography. Administration of T3 and T4 suppressed the basal and the ACTH-stimulated levels of plasma corticosterone. In ZFR cells, both thyroid hormones inhibited ACTH-stimulated corticosterone secretion, but the basal corticosterone was inhibited only with T3 > 10(-10) M or T4 > 10(-8) M. Likewise, T3 or T4 at 10(-7) M inhibited the basal- and ACTH-stimulated levels of intracellular cAMP. Physiological doses of T3 and T4 decreased the activities of 3 beta-hydroxysteroid dehydrogenase, 21-hydroxylase, and 11 beta-hydroxylase. These results suggest that thyroid hormones counteract ACTH in adrenal steroidogenesis through their inhibition of cAMP production in ZFR cells.

Thyroid hormone-induced plasticity in the adult rat brain

It is well known that thyroid hormone plays a crucial role in the development and maturation of the nervous system. However, little is known about the role of thyroid hormone in the adult brain. In this short review we have dwelt on this point, with regard to the role of thyroid hormone on neuropeptide gene expression regulation in the paraventricular nucleus of the hypothalamus and in extrahypothalamic brain areas, on neurotrophin and neurotrophin receptor expression in the hippocampus and basal forebrain in basal conditions, and after neurotoxic challenges. Effects of hypothyroidism are discussed in view of a possible role of thyroid status in brain aging quality.

NGF content and expression in the rat pituitary gland and regulation by thyroid hormone

The involvement of nerve growth factor (NGF) in neuroendocrine regulation is supported by several lines of evidence. In this paper, we investigated the NGF content and expression in the pituitary gland and other endocrine organs during dysendocrine states (thyroidectomized, adrenalectomized and gonadectomized male rats). We found an increase of NGF-IR in the pituitary gland and testis of hypothyroid rats whereas no differences were found in the adrenal gland and blood. Also, NGF mRNA expression had increased in the anterior pituitary of hypothyroid rats whereas it had not changed after adrenalectomy and gonadectomy. Moreover, other neurotrophins and neurotrophin high-affinity receptors were unchanged in the anterior pituitary of hypothyroid rats. These data indicate that pituitary NGF is selectively modulated by thyroid status of the animal, further supporting a close link between NGF and thyroid hormone.

Thyrotropin-releasing hormone gene expression in the human hypothalamus

We studied the distribution of mRNA coding for thyrotropin-releasing hormone (TRH) in the human hypothalamus by means of in situ hybridization. In 10% formalin-fixed paraffin-embedded tissue sections of five hypothalami, TRH mRNA-containing cells were found in several nuclei and areas. Numerous TRH mRNA-containing cells were detected in the medial region of the caudal part of the paraventricular nucleus. These neurons were heavily labeled and mainly small to medium-sized. Few, lightly- and medium-labeled, small cells were detected in the suprachiasmatic nucleus. In addition, heavily labeled single cells were found in the perifornical area and the anterior- and lateral hypothalamic regions. In the latter region, occasional heavily labeled cells were found just dorsal to the supraoptic nucleus. Neither in the supraoptic nucleus nor in the sexually dimorphic nucleus of the preoptic area were TRH mRNA-containing cells found. This is the first description of TRH mRNA containing cells in the human hypothalamus.

Psychological and endocrine abnormalities in refugees from East Germany: Part II. Serum levels of cortisol, prolactin, luteinizing hormone, follicle stimulating hormone, and testosterone

We investigated afternoon serum levels of cortisol, prolactin, luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone in a group of 84 refugees who had fled from East to West Germany and suffered from psychiatric disorders within 6 weeks of their arrival in West Berlin. The mean hormone levels were compared with those of healthy control subjects. Cortisol levels were lower and LH levels were higher in the patients than in the control subjects, but only at trend levels of significance. No differences were found between the prolactin, FSH, or testosterone concentrations of the two groups. The patients with major depressive disorder (MDD) had a significantly higher mean cortisol level than the mean levels in the subgroups in whom posttraumatic stress disorder, dysthymia, and adjustment disorder were diagnosed. It can be concluded that the hypothalamic-pituitary-adrenal axis may "adapt" during severe long-term psychological stress and that long-term stress may be only one of the neurochemical mechanisms underlying the hypercortisolemia in patients with MDD.

Superoxide dismutase activation in thyroid and suppression in adrenal. Novel pituitary regulatory routes

This study reports that administration of TSH in young female mice results in a concomitant augmentation of SOD activity in the thyroid gland. A strong thyroid-adrenal interdependence was also evident in the form of a marked loss of SOD activity in the adrenal gland in response to TSH administration. Very recently SOD/O2.- system had been identified as a potent H2O2 generator which provides substrate for the action of key enzyme in thyroxine and progesterone biosynthesis, viz. the peroxidase. Thus, these results strongly suggest that trophic hormones tonically stimulate hormone biosynthesis by modulating activation/suppression of specific enzymes, which could be the basis of the tuning sequence.