Thyrotropin-releasing hormone potently reverses epinephrine-stimulated hyperglycemia in mice

Intracerebroventricular microinjection of thyrotropin-releasing hormone (TRH) potently blocked the development of, as well as promptly reversed, epinephrine-stimulated hyperglycemia in mice. The central antihyperglycemic effect was dose-related (0.1-10 micrograms), could be reproduced by an intravenous injection of a large dose of the peptide (100 micrograms), was independent of experimental factors such as stress and age, was effective against other hyperglycemic stimuli, and appeared to be unique to TRH, as it could not be mimicked by many other centrally active peptides known to influence glucoregulation in normoglycemic animals. Moreover, the antihyperglycemic effect of TRH appeared to depend on the structural integrity of the peptide molecule but seemed to be unrelated to the peptide's hypophysiotropic actions or to interaction of the peptide with previously characterized TRH receptors, as it could be mimicked by various analogs devoid of thyrotropin- and prolactin-releasing influences or by peptides resembling TRH in amino acid composition but lacking substantial binding affinity to TRH receptors. Furthermore, the effect of TRH to reverse epinephrine-stimulated hyperglycemia appeared to be mediated by combined action of peripheral sympathetic and parasympathetic mechanisms to stimulate insulin release from the pancreas, since only complete blockade of the central autonomic outflow, but not selective perturbation of the sympathetic or parasympathetic outflow, or depletion of pancreatic insulin could substantially attenuate the antihyperglycemic action. Taken together, these results suggest a new physiologic role of TRH as a central glucoregulatory neuropeptide involved in autonomic modulation of insulin secretion and prevention of hyperglycemia.     

Central thyrotropin-releasing hormone elicits systemic hypoglycemia in mice

Thyrotropin-releasing hormone (TRH), injected into the central nervous system (CNS) in rats, has been shown to elicit systemic hyperglycemia. In the present study, central TRH administration significantly decreased the plasma glucose in mice. The hypoglycemic response could be blocked by pretreatment with the muscarinic cholinergic antagonist, atropine methyl bromide, or the diabetogenic β-cytotoxin, alloxan, implicating the involvement of the parasympathetic system and insulin-secreting cells in the endocrine pancreas. The role of TRH in the CNS in the autonomic regulation of glucose homeostasis is discussed.     

Effect of enhancement of cholinergic tone on the growth hormone response to acute hyperglycaemia or thyrotropin-releasing hormone in dogs

The effect of enhancement of cholinergic tone by pyridostigmine on the growth hormone (GH) response to thyrotropin-releasing hormone (TRH) or glucose-induced acute hyperglycaemia was tested in six adult unanaesthetized beagle dogs. Both TRH (5μg/ kg iv) and glucose (2 g/kg orally) did not significantly alter baseline GH levels but reduced the GH response to GH-releasing hormone (GHRH) (2 μg/kg iv), although this effect was more clear-cut with TRH than with glucose. Pretreatment with pyridostigmine (2 mg/kg orally) counteracted the inhibitory effect of hyperglycaemia on the GHRH-induced GH release, but had no effect on the inhibition induced by TRH. In summary, these results indicate that: 1) acute hyperglycaemia and TRH play an inhibitory role on GHRH-stimulated GH secretion in dogs; 2) the inhibitory effect of acute hyperglycaemia is mediated via hypothalamic cholinergic neurotransmission, whereas other neurotransmitter pathways would be. involved in the effect of TRH.     

Structure-activity relationships of TRH analogs in rat spinal cord injury

Effects of thyrotropin-releasing hormone (TRH) analogs were compared in rats to evaluate the structure-activity relationships of such compounds in the treatment of traumatic spinal cord injury. CG3703, a TRH analog having a modified amino-terminus, significantly improved motor recovery and somatosensory-evoked responses after trauma; in contrast, RX77368, which has a modified carboxy-terminus, was without effect, even at doses up to 10 mg/kg. These findings confirm and extend findings in cats, using other TRH analogs in a different model of spinal trauma. Together, data from rat and cat studies are consistent with the hypothesis that the integrity of the C-terminal amino acid may be critical for the beneficial effects of treatment with TRH and TRH analogs in experimental spinal injury, and suggest that a variety of other TRH analogs having substitutions of the pyroglutamyl or histidyl moieties of the tripeptide may also prove to be effective in the treatment of such injury.     

Systemic administration of thyrotropin-releasing hormone enhances striatal dopamine release in vivo

We examined the effects of systemically administered thyrotropin-releasing hormone (TRH) on the release of dopamine (DA), as assessed by brain microdialysis within the corpus striatum of anesthetized rats. A single dose (10 micrograms i.v.) elevated DA levels in brain extracellular fluid (ECF) by 240% above baseline levels after 150 min. Systemic tyrosine ([TME] 20 mg/kg i.v.) also increased DA release (by 190% after 150 min), while combined treatment with both agents was associated with significant potentiation of the DA response (to 640% after 150 min). None of the treatments significantly altered striatal tissue levels of DA or its metabolites. A large dose of TRH (50 micrograms i.v.) significantly increased DA release (by 1150%) whether or not animals had received an active or denatured prolactin (PRL) antiserum prior to the experiment, suggesting that the TRH effect is not mediated by PRL. Although TRH is rapidly metabolized in plasma and penetrates the blood-brain barrier only poorly, our results suggest that even relatively small doses of the hormone can affect striatal dopaminergic neurotransmission.     

Immunological blockade of endogenous thyrotropin-releasing hormone produces hypothermia in rats

Administration of anti-serum to thyrotropin-releasing hormone (TRH) into the lateral cerebral ventricle of rats produces a dose-dependent hypothermia. Neutralization of anti-TRH serum with excess TRH abolishes this hypothermic effect. These results suggest a thermoregulatory role for endogenous TRH in the rat central nervous system.     

Thyrotrophin-Releasing Hormone Raises Cytosolic Free Calcium Concentration in Human Adenomatous Somatotrophs and Corticotrophs; Comparison with in vivo Responsiveness to Thyrotrophin-Releasing Hormone in Patients with Acromegaly or Cushing's Disease

The effect of thyrotrophin-releasing hormone (TRH) on intracellular free Ca²⁺ concentration, [Ca²⁺)i, was investigated with the fluorescent dye fura-2 in cell suspensions obtained from 13 human growth hormone-secreting adenomas and 6 adrenocorticotrophin-secreting adenomas. Preoperatively, 9 out of 13 acromegalic patients showed a positive growth hormone response to TRH administration while none of the 6 patients with Cushing's disease had a plasma adrenocorticotrophin increase after TRH injection. In all the growth hormone-secreting adenomas the addition of TRH (100 nM) caused a significant rise in [Ca²⁺]i (from a resting level of 133±40 (±SD) to a value of 284±119 nM at 100 nM TRH, n = 42; P<0.001). The transient induced by TRH was found to have a dual origin, one due to Ca²⁺ mobilization from intracellular stores which was maintained in presence of EGTA (3mM) and verapamil (10 μM) and a plateau phase due to Ca²⁺ influx from the extracellular media. Somatostatin (0.1 μM) lowered both resting [Ca²⁺]i and TRH-induced transients. The effect of gonadotrophin-releasing hormone on [Ca²⁺]i was evaluated on cell suspensions obtained from 6 growth hormone-secreting adenomas. Gonadotrophin-releasing hormone (100 nM) caused a marked rise in [Ca²⁺]i (from 179±25 to 283±15nM) on the cell suspension obtained from the only in vivo responsive adenoma while it was ineffective in the remaining 5. Although TRH was ineffective in modifying plasma adrenocorticotrophin levels in all patients with Cushing's disease, in 5 out of 6 tumors the addition of 100 nM TRH caused a significant rise in [Ca²⁺]i (from 102.5 ± 36 to 163±66 nM, n = 22; P < 0.005). However, the effect of TRH on [Ca²⁺]i was significantly lower than that caused by arginine vasopressin, a physiological stimulator of adrenocorticotrophin release ([Ca²⁺]i values; 145±78 nM at 100 nM TRH versus 300±140 at 10 nM arginine vasopressin, n = 15; P<0.05). Moreover, the effect of arginine vasopressin on [Ca²⁺]i was detectable at concentrations as low as 0.1 nM while TRH was effective at concentrations higher than 1 nM. By contrast, gonadotrophin-releasing hormone was ineffective in increasing [Ca²]i in all the adrenocorticotrophin-secreting adenomas studied. Collectively, these data indicate that sensitivity to TRH is present in almost all the growth hormone- and adrenocorticotrophin-secreting adenomas independently of the responsiveness of the individual patients to the peptide.     

Growth hormone (GH) release following thyrotropin-releasing hormone (TRH) injection in manic patients receiving lithium carbonate

(1) The effect of intravenous injection of synthetic TRH (500 μg) on the plasma GH was investigated in six patients in the manic state and five normal volunteers, both before and during lithium treatment, for 3–4 weeks. (2) TRH caused a significant increase in plasma GH in four out of six manic patients during lithium treatment. (3) TRH only raised plasma GH in one patient before lithium treatment. (4) No appreciable change was noted in normal subjects either before or during lithium treatment. (5) The positive GH responses to TRH in manic patients on lithium were observed 90–120 min after TRH except for one patient. (6) The delayed GH response may be caused by secondary effects of TRH on brain monoamine neurotransmitters, rather than by a direct action of TRH on the pituitary.     

The involvement of pineal gland and melatonin in immunity and aging. I. Thymus-mediated, immunoreconstituting and antiviral activity of thyrotropin-releasing hormone

Circadian, continued treatment with melatonin during the dark cycle produces changes in the blood level of thyroid hormones in aging mice. Thyroid-stimulating hormone (TSH) and thyrotropin-releasing hormone (TRH) antagonize the involution of the thymus produced by prednisolone. This effect of TRH does not seem thyroid dependent. TRH restores antibody production in non-responder athymic nude mice but does not exert this effect in neonatally thymectomized mice. Moreover, this activity does not correlate with thyroxine levels. TRH exerts a powerful protective effect in mice challenged with encephalomyocarditis (EMC) virus. Presumably pineal melatonin exerts its varied regulatory functions via hypothalamic TRH.     

TRH concentration in rat olfactory bulb is undiminished by deafferentation

The effect of deafferentation of the rat olfactory bulb on bulbar TRH concentration was studied. TRH concentrations in the lesioned bulbs did not decline when compared to concentrations in sham-lesioned bulbs for the post-lesion intervals of 1 h through 14 days. Since TRH concentrations did not decline following deafferentation, TRH in the olfactory bulb does not derive from centrifugal neurons.     

卡马西平与TRH抗癫痫作用相互关系的研究

目的探讨卡马西平与促甲状腺素释放激素（ＴＲＨ）抗癫痫作用的相互关系。方法采用放射免疫分析法测定戊四氮（ＰＴＺ）急性致病大鼠海马ＴＲＨ的含量。结果急性致痫后,海马内ＴＲＨ表达水平在２小时未见明显变化,４８小时显著升高。卡马西平预处理组在痫性发作后４８小时海马内ＴＲＨ表达水平明显升高,与对照组及假模型组相比均有显著性差异。结论卡马西平能显著升高痫性发作对ＴＲＨ的诱导表达,ＴＲＨ与卡马西平的作用可能有重     

Hormone release in depressed patients before and after recovery.

(1) In 19 deeply depressed patients suffering from primary affective disorders, the thyroid stimulating hormone (TSH) and prolactin (hPRL) responses to thyrotrophin releasing hormone (TRH) were measured. In ten of them, the growth hormone (hGH) and cortisol responses to hypoglycaemia (ITT) were also determined. (2) In the depressed state, TSH secretion was extremely low or non-existent and hPRL was below normal. Half of the tested patients had zero or subnormal hGH secretion in response to hypoglycaemia. (3) After recovery, 16 of these patients were retested by TRH injection. TSH responses showed a fourfold increase and hPRL showed an increase of 45%. In the seven retested by ITT, the mean hGH response was not different, but the three previous non responders, herein included, were normalized. In all seven, the fall in glycaemia was more marked and the cortisol discharge was more sustained. (4) These findings draw attention to (a) the high frequency of alterations in the functional endocrine tests in depressed patients, (b) the discrepancy between these observations and the absence of any overt clinical signs of endocrine disease in these subjects, (c) the interest in using the patient as his own control, (d) the reversible nature of these alterations after recovery.     

The combined use of immunohistochemistry and intracellular staining with horseradish peroxidase for light and electron microscopic studies of transmitter-identified inputs to functionally characterized neurons

Physiologically identified triceps surae alpha motoneurons in the cat were stained intracellularly with horseradish peroxidase (HRP). After fixation with 2% glutaraldehyde and treatment with sodium borohydride, spinal cord sections were incubated with rabbit antiserum against thyrotropin-releasing hormone (TRH) and rabbit peroxidase-antiperoxidase complex. Light microscopically detected close contacts between immunoreactive nerve terminals and intracellularly HRP-stained profiles were studied under the electron microscope. In this way, synaptic contacts between TRH-immunoreactive boutons and functionally characterized alpha motoneurons could be demonstrated.     

Thyrotropin-releasing hormone (TRH) content of rat striatum: Modification by drugs and lesions

Two hours after injection, D-amphetamine sulfate (10 mg/kg, i.p.) lowered thyrotropin-releasing hormone (TRH) levels in rat striatum by 50%, but produced no significant changes in the TRH contents of hypothalamus, septum, brain stem or preoptic area. The effect peaked 2 h after amphetamine injection and declined slowly thereafter. The amphetamine-induced decrease in striatal TRH could be blocked by pretreatment with haloperidol or alpha-methyltyrosine, or by production of a 6-hydroxy-dopamine lesion in the ipsilateral substantia nigra. Amphetamine did not act by inhibiting protein synthesis in as much as cycloheximide did not similarly decrease striatal TRH. Kainic acid injected into the striatum lowered TRH by 30% after 5 days. In contrast, partial deafferentiation of the striatum (by cerebral hemitransection at mid-hypothalamic level) increased striatal TRH 2-3-fold, while lesions of the dorsal raphe did not significantly change striatal TRH. Thus TRH levels in rat striatum are closely regulated by dopaminergic and other neurotransmitter systems.     

Cold stress induces metabolic activation of thyrotrophin-releasing hormone-synthesising neurones in the magnocellular division of the hypothalamic paraventricular nucleus and concomitantly changes ovarian sympathetic activity parameters

Recent studies suggest thyrotrophin-releasing hormone (TRH) serves as a neurotransmitter and thereby provides a functional vegetative connection between the brain and the ovary. In the present study, magnocellular neurones of the paraventricular nucleus (PVN) in animals subjected to cold exposure were studied to determine the hypothalamic origin of the TRH involved in this pathway. In situ hybridisation analysis of hypothalamic tissue showed that cold exposure causes a two-fold increase in the total number of neurones expressing TRH mRNA in the PVN. Immunohistochemical studies showed that TRH peptide is localised to the magnocellular PVN and that the number of TRH immunoreactive cells increases two-fold following 64 h of cold exposure. Double-immunostaining for MAP-2 and TRH revealed that TRH peptide is localised in the perikarya of the magnocellular neurones. TRH release was measured in vivo from the magnocellular portion of the PVN using push-pull perfusion. Although controls exhibited a very low level of TRH release, animals subjected to cold showed a pulsatile-like TRH release profile with two different patterns of release: (i) low basal level with small bursts of TRH release and (ii) a profile with an up to seven-fold increase in TRH release compared to controls. The colocalisation of TRH with the specific somato-dendritic marker MAP-2 in processes of the magnocellular neurones suggested a local release of TRH. Additional studies demonstrated a reduction in ovarian noradrenaline content after 48 h of cold exposure, a feature indicative of nerve activation at the terminal organ. After 64 h of cold exposure, the ovarian noradrenaline returned to control values but the noradrenaline content of the coeliac ganglia was increased, suggesting a compensatory effect originating in the cell bodies of the sympathetic neurones that innervate the ovary. The correlation between the local release of TRH from dendrites within the magnocellular PVN in conditions of cold and the activation of the sympathetic nerves supplying the ovary raises the possibility that TRH contributes to the processing regulating sympathetic outflow and may thereby impact on the functional activity of the ovary.     

纤维肌痛患者血清中三种促激素释放激素含量的改变

目的 探讨纤维肌痛患者血清中促肾上腺皮质激素释放激素(CRH)、促甲状腺激素释放激素(TRH)和促性腺激素释放激素(GnRH)含量变化及其临床意义。方法 选取2009年6月至2010年10月在安徽医科大学附属第一医院神经内科就诊的纤维肌痛患者26例及同期健康体检者29名,分别作为患者组及对照组,用汉密尔顿抑郁量表-17评估患者的抑郁状况。采取ELISA方法检测两组血清中CRH、TRH和GnRH含量,所得数据分别采用独立样本t检验(正态分布)与MannWhitney Test检验(非正态分布),同时用受试者工作特征(ROC)曲线分析3种激素对纤维肌痛诊断的特异度和敏感度,并采取Spearman相关性分析探讨3种激素含量与患者年龄、性别、压痛点个数、疼痛程度及抑郁程度的相关性。结果 与对照组[70.0(48.7,78.0) ng/L]相比,纤维肌痛患者血清中CRH含量明显升高[271.9(210.9,326.5)ng/L,x2=6.408,P＜0.01],TRH[分别为(82.7±6.9)、(87.2±6.8)ng/L,t =2.560,P＜0.05]及GnRH[分别为(18.2±0.9)、(19.9±1.6) ng/L,t=5.324,P＜0.01]含量也显著性升高。三者均与疼痛程度和压痛点个数正相关,CRH和GnRH含量还与患者抑郁程度正相关。血清中3种激素含量的诊断敏感度和特异度ROC曲线下面积分别为1.000、0.684与0.854。结论 纤维肌痛患者CRH、TRH和GnRH分泌增多,其中CRH的值可能可以作为诊断纤维肌痛的参考指标。     

Thyrotropin releasing hormone (TRH) in the hippocampus of Alzheimer patients

Thyrotropin-releasing hormone (TRH) is best known for its hypothalamic neuroendocrine role in regulating thyroid function. In extra-hypothalamic regions in vitro, we have shown TRH to have a protective effect against synaptic loss and neuronal apoptosis. A role for TRH in Alzheimer's disease (AD) has not been established previously. In this study, we examined the content of the TRH peptide in the hippocampus of elderly controls (n=5) and AD patients (n=7) by radioimmunoassay (RIA). The TRH concentration was decreased in the AD hippocampus compared to normal elderly controls (p < 0.01). In a separate series of experiments utilizing primary cell cultures made from rat hippocampus, TRH peptide concentration was depleted by the addition of TRH antiserum. TRH withdrawal was found to enhance the activity of glycogen synthetase kinase-3 (GSK-3beta), a critical enzyme necessary for the phosphorylation of tau, as well as the phosphorylation of the tau protein itself. This TRH depletion induced upregulation in phosphorylation that was observed to initiate axonal retraction in cultured neurons. These data suggest that TRH within the hippocampus can regulate the activity of various proteins by phosphorylation/dephosphorylation that may be involved in the pathogenesis of AD.     

The effect of repeated thyrotropin-releasing hormone administration on regional cerebral blood flow in humans

Recently, regional cerebral blood flow (rCBF) was found to increase slightly in the thalamus after a single administration of thyrotropin-releasing hormone (TRH) to healthy adults. Regarding the effect of prolonged TRH administration on rCBF, some scintigraphic improvements have been observed recently. However, no study has investigated the effect quantitatively, except for a preliminary study by positron emission tomography. Therefore, we examined the effect of repeated administration of TRH on rCBF in humans quantitatively. Eight patients with spinocerebellar degeneration (SCD) were given TRH intravenously at a daily dose of 2 mg for 14 days and rCBF was measured by the ¹³³Xe intravenous injection method before and after repeated TRH administration. TRH caused a significant (p < 0.01) increase of 12% in the gray matter flow (fast flow, F|), especially at the parietal and occipital lobes, and also caused a significant (p < 0.05) increase of 8% in the initial slope index (ISI), especially at the parietal lobe. Among seven patients who improved clinically after TRH administration, F₁ values were increased in all of them and ISI values were increased in six. We conclude that repeated TRH administration increases rCBF in humans. These results might warrant clinical investigation of a possible therapeutic role of TRH in patients with cerebral ischemia.     

Pyridostigmine, an Acetylcholinesterase Inhibitor, Stimulates Growth Hormone Release, but has no Effect on Basal Thyrotrophin or Adrenocorticotrophin Levels, or the Thyrotrophin Response to Thyrotrophin-Releasing Hormone

Pyridostigmine, an acetylcholinesterase inhibitor, stimulates growth hormone (GH) release and is thought to act by inhibiting hypothalamic somatostatin release. There are few data concerning the effect of pyridostigmine on other pituitary hormones apart from GH. We have studied the effect of pyridostigmine on basal GH, thyrotrophin (TSH), prolactin, adrenocorticotrophin and cortisol release, and thyrotrophin-releasing hormone (TRH)-stimulated TSH and prolactin release, in two studies involving nine healthy male subjects. Pyridostigmine stimulated GH release in all subjects but had no effect on adrenocortocotrophin or cortisol levels, or basal or TRH-stimulated TSH and prolactin levels. There are some data to suggest that somatostatin inhibits TRH-stimulated TSH release. Our findings, however, suggest that either endogenous somatostatin tone has little effect on the TSH response to TRH compared to its effects on GH or pyridostigmine acts through a mechanism other than altering somatostatin tone. Pyridostigmine did not alter adrenocorticotrophin or cortisol levels in the presence of a clear action on GH release, providing further evidence that the previously reported effects of cholinergic drugs on cortisol release are stress-related.