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.     

Immunocytochemistry of thyrotropin-releasing hormone in the rabbit medulla oblongata

The distribution and ultrastructure of thyrotropin-releasing hormone-like immunoreactive (TRH-LI) neurons were examined in rabbit medulla oblongata. TRH-LI cell bodies were located in the ventral region of the medulla oblongata: in the paraolivary and parapyramidal regions, regions in and around the pyramidal tract, the dorsolateral region of the lateral reticular nucleus, and the raphe nuclei. The paraolivary and parapyramidal regions contained most of the TRH-LI cell bodies in the medulla oblongata. TRH-LI neurons processes were densely distributed in the dorsal vagal complex and the area postrema. Electron-microscopic immunocytochemical studies revealed TRH-LI neurons at the obex level in the paraolivary region of rabbits. TRH-like immunoreactivity was localized in larger granular vesicles. TRH-LI somata and dendrites received synaptic inputs from both TRH-LI and unlabeled axon terminals. More than half of the TRH-LI axon terminals made synapses with somata or processes of TRH-LI neurons. These observations, together with previous reports that TRH causes respiratory facilitation, suggest that TRH-LI neurons in the paraolivary region in rabbits may be involved in respiratory functions.     

Post-translational processing of thyrotropin-releasing hormone precursor in rat brain: identification of 3 novel peptides derived from pro TRH

The sequence of rat hypothalamic pro-thyrotropin releasing hormone, deduced by sequencing of cDNA, in addition to 5 TRH progenitor genitor sequences contains leader, trailer and 4 intervening sequences separated by paired basic amino acid sequences. We have developed radioimmunoassays to synthetic peptides corresponding to portions of these cryptic proTRH sequences and have used these assays to identify and partially characterize proTRH peptides, distinct from TRH, in extracts of rat brain. Two of these peptides correspond closely in size to one intervening sequence and the car☐y-terminal sequence of proTRH. Three other peptides correspond to the intact amino-terminal leader sequence and two peptides formed by a further cleavage of the leader sequence at an internal paired basic amino acid sequence.     

Antiepileptic effects of thyrotropin-releasing hormone and its new derivative, DN-1417, examined in feline amygdaloid kindling preparation

The comparative antiepileptic effects of the thyrotropin-releasing hormone and its new derivative, gamma-butyrolactone-gamma-carbonyl-L-histidyl-L-prolinamide citrate (DN-1417), were examined in feline amygdaloid kindling preparations. When tested in kindled animals, both agents showed a transient and non-dose-dependent anticonvulsant effect, in addition to raising the generalized convulsive seizure-triggering threshold for a prolonged period of time. Furthermore, DN-1417 exerted a significant effect on postictal events: shortening the electrographic silence, leaving the duration of slow activity intact, while prolonging the period of seizure refractoriness. When tested in kindling animals, DN-1417 showed a significant but non-dose-dependent prophylactic effect on both primary and secondary amygdaloid sites.     

Intranasal delivery of a thyrotropin-releasing hormone analog attenuates seizures in the amygdala-kindled rat

PURPOSE: Thyrotropin-releasing hormone (TRH) is known to have anticonvulsant effects in several animal seizure models and is efficacious in treating patients with certain intractable epilepsies. However, the duration of TRH's action is limited due to low bioavailability and difficulty penetrating the blood-brain barrier (BBB). Since direct nose to brain delivery of therapeutic compounds may provide a means for overcoming these barriers, we utilized the kindling model of temporal lobe epilepsy to determine if intranasal administration of a TRH analog, 3-methyl-histidine TRH (3Me-H TRH), could significantly inhibit various seizure parameters. METHODS: Kindling was accomplished using a 1s train of 60 Hz biphasic square wave (200 microA peak to peak) administered daily to the basolateral amygdala until the animal was fully kindled. Afterdischarge duration (ADD) was assessed via electroencephalographs (EEGs) recorded bilaterally from bipolar electrodes in the basolateral amygdala and behavioral seizure severity (stage I-V) was simultaneously recorded digitally. Kindled subjects received 3Me-H TRH (10(-9), 10(-8), 10(-7) M) intranasally 60 and 30 min prior to amygdala stimulation. The ADD and seizure stage was compared to control kindled animals receiving physiological saline intranasally. RESULTS: Intranasal application of 3Me-H TRH resulted in a concentration-dependent reduction in total seizure ADD. Additionally, the analog had significant concentration-dependent effects on behavioral stages I through IV (partial) and stage V (generalized) seizures. However, 3Me-H TRH significantly reduced clonus duration only at the highest concentration. DISCUSSION: The results indicate that intranasal delivery of TRH/analogs may be a viable means to suppress temporal lobe seizures and perhaps other seizure disorders.     

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.     

Hypothalamic thyrotropin-releasing hormone (TRH)-containing neurons involved in the hypothalamic-hypophysial-thyroid axis. Light microscopic immunohistochemistry

The localization of neurons containing immunoreactive thyrotropin-releasing hormone (TRH) was examined in the hypothalamus of intact, propythiouracil (PTU)-treated, and colchicine-treated adult rats. In intact animals, immunoreactive TRH neurons were occasionally found in the paraventricular and dorsomedial nuclei and in the anterior and lateral hypothalamic areas. In PTU-treated animals, the cellular appearance of the hypothalamus with the exception of the paraventricular nucleus was almost similar to that of intact animals. In the paraventricular nucleus, only the cells localized in the periventricular and medial parvocellular subdivisions significantly increased in number and became hypertrophic in comparison with intact animals. The distribution of immunoreactive fibers in the hypothalamus was almost equal among the 3 animal groups with the exception of that in the median eminence, in which the fibers were most densely concentrated in intact animals, and most sparse in PTU-treated rats. The fibers projecting into the median eminence were distinguished into the periventricular and lateral pathways, which are derived from the neurons in the periventricular and medial parvocellular subdivisions of the paraventricular nucleus, respectively. Thus, among immunoreactive TRH neurons in the hypothalamus, only those in the periventricular and medial parvocellular subdivisions of the paraventricular nucleus may be involved in the hypothalamic-hypophysial-thyroid axis.     

A comparison of the effects of serotonin, substance P and thyrotropin-releasing hormone on excitability of rat spinal motoneurons in vivo

Lumbar spinal motoneurons of urethane-anesthetized rats were driven at stable low firing rates by automatically cycled iontophoretic applications of glutamate or aspartate. The effects of iontophoretically applied serotonin, substance P or thyrotropin-releasing hormone (TRH) on glutamate or aspartate-evoked activity were then tested. All 3 substances were found to enhance both glutamate- and aspartate-induced excitation of the motoneurons. This enhancement of excitability was usually preceded by a brief period of inhibition at current onset. Although the effects of serotonin and substance P were qualitatively remarkably similar, TRH differed in that TRH occasionally inhibited motoneuron excitability without subsequent facilitation, and tachyphylaxis developed for the facilitatory effects of TRH. After TRH desensitization, serotonin could still enhance spinal motoneuron excitability.     

Intrathecal thyrotropin-releasing hormone therapy of amyotrophic lateral sclerosis

Summary Six patients with amyotrophic lateral sclerosis were given from 800 to 4000 g of thyrotropin-releasing hormone (TRH) intrathecally for a period of 2–6 months. The progressive course of this disease, manifested by increasing atrophy, paralysis and disability score, was not altered. This supports the hypothesis that the decrease in TRH content in the anterior horn region is secondary to the cellular destruction. TRH appears to play no significant role in the pathogenesis of amyotrophic lateral sclerosis     

Early postnatal administration of 5,7-dihydroxytryptamine: Effects on substance P and thyrotropin-releasing hormone neurons and terminals in rat brain

Substance P, thyrotropin-releasing hormone (TRH) and serotonin are putative neurotransmitters which have been proposed to co-exist in some brain neurons. Our previous immunocytochemical and biochemical studies have demonstrated that 85–100% of all serotonin neurons are destroyed following neonatal 5,7-dihydroxtryptamine (5,7-DHT) treatment. In this study, we have determined the effect of neonatal 5,7-DHT and desipramine (DMI) treatment on the biochemical content and immunocytochemical localization of substance P and TRH throughout the brain. Interestingly, we have observed that virtually all substance P- and TRH-immunoreactive cells in the ventral pons-medulla are destroyed by the neurotoxin. However, peptide-containing neurons in other regions were not affected. Additionally, we measured the peptide content and found that TRH is significantly altered in any region, even after a pons-medulla (−20%), but not in other brain regions. Substance P content was not significantly altered in any region, even after a greater than 90% reduction of serotonin. These data indicate that the co-localized substance P and TRH forms a small porportion of the total peptide in brain.     

The thyrotropin-releasing hormone test in the diagnosis of unipolar depression

The establishment of criteria for a blunted thyroid-stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) may prove useful in distinguishing patients with major unipolar depression from patients with nonmajor depressions and controls. To this end, we administered the TRH test to a group of depressed, euthyroid inpatients diagnosed by Research Diagnostic Criteria and 20 normal volunteer controls. The mean maximal TSH response (delta TSH) to infusion of 500 micrograms of TRH of 7.3 +/- SD 4.6 microIU/ml in the 105 patients with major depressive disorder, primary unipolar subtype was significantly lower than that of 13.4 +/- SD 4.4 in the 20 controls and 10.9 +/- SD 4.4 in the 40 patients with nonmajor depressions. The differences were not explainable by differences in baseline thyroid function, age, or sex. When a delta TSH less than or equal to 7.0 microIU/ml was used as a diagnostic test for unipolar depression, the sensitivity of the TRH test was 56%, the specificity 93%, and the predictive value 91%. These results suggest that the TRH test may be useful in confirming the diagnosis of major unipolar depression and hence identifying patients likely to respond to antidepressant medications or electroconvulsive therapy.     

Excitatory effects of thyrotropin-releasing hormone on neurons within the nucleus ambiguus of adult guinea pigs

The electrophysiological effects of thyrotropin-releasing hormone (TRH) on neurons within the nucleus ambiguus (NA) of adult guinea pigs were studied using an in vitro brain stem slice preparation. In 0.01–1.0 μm TRH, NA neurons depolarized (25/39), expressed enhanced postinhibitory rebound (8/8 tested), or exhibited oscillations of the membrane potential (17/39). Because the amplitude of postinhibitory rebound in tetrodotoxin (TTX) at various membrane potentials was not altered by TRH, it suggests that TRH enhanced postinhibitory rebound indirectly by depolarizing the cell membrane. The membrane potential oscillations in NA neurons were persistent in TTX and their frequency was dependent on the membrane potential, suggesting that these oscillations were due to intrinsic membrane properties and not to synaptic inputs. The excitation of NA neurons in vitro by TRH suggests that endogenous TRH may modulate the activity of neurons involved in the regulation of respiratory and autonomic function.     

Immunological blockade of endogenous thyrotropin-releasing hormone impairs recovery from hyperglycemia in mice

Administration of antiserum to thyrotropin-releasing hormone (TRH) into the lateral cerebral ventricle of mice significantly attenuated recovery from hyperglycemia induced by treatment with 2-deoxyglucose but had no effect on the plasma glucose of saline-treated mice. TRH, injected centrally together with the anti-TRH antibody, reversed the effect of the antiserum and blocked the development of hyperglycemia. These findings suggest that activation of TRH neurons in the central nervous system may be a physiological event influencing recovery from hyperglycemia.     

A reliable method for the quantification of thyrotropin-releasing hormone (TRH) in tissue and biological fluids

A reliable technique for purification of crude tissue extracts and analysis for TRH by HPLC, TLC, radioimmunoassay and bioassay is presented. We conclude that authentic TRH is present throughout the mammalian brain and accounts for much of the TRH-like immunoreactivity in several peripheral organs, but that it is not present in urine, placenta, or pineal, and its concentration in blood is some 250-fold less than a value obtained from a direct radioimmunoassay of a sample of blood.     

Diagnostic and therapeutic value of testing stimulation of thyroid-stimulating hormone by thyrotropin-releasing hormone in 100 depressed patients

The thyrotropin-releasing hormone (TRH) test was performed in 100 depressed patients, including 73 patients with a major depressive episode (MDE) according to DSM-III. Thirty-one patients subsequently received an antidepressant with a predominant serotoninergic action (indalpine or citalopram), and 27 patients received a noradrenergic antidepressant (maprotiline). The diagnostic value of the TRH test was not conclusive for any of the subgroups of depressed patients: MDE, MDE with melancholia or MDE in bipolar patients. Similarly, the value of the TRH test in the choice of antidepressant treatment according to the monoaminergic action was not convincing. These results are discussed in the light of the data of the international literature.     

Microinjection of thyrotropin-releasing hormone in the paraventricular nucleus of the hypothalamus stimulates gastric contractility

Changes in gastric contractility following microinjection of thyrotropin-releasing hormone (TRH) into the paraventricular nucleus of the hypothalamus (PVN) were examined in fasted, urethane-anesthetized rats. Gastric contractility was measured with extraluminal force transducers and analysed by computer. Unilateral and bilateral PVN microinjections of TRH (0.5 and 1.0 μg) significantly increased the force index of gastric contractions from 0 to 60 min postinjection, when compared with animals microinjected with 0.1 μg TRH, 0.1% BSA or TRH (0.5 and 1.0 μg TRH) in sites adjacent to the PVN. The gastric force index was also significantly elevated from 61 to 120 min postinjection in rats receiving bilateral PVN microinjections of TRH (0.5 and 1.0 μg). Peak gastric responses occurred within 10–20 min postinjection and represented an approximately eight-fold increase over basal values. In the remaining groups, the force index was not significantly altered from preinjection values. The excitatory action of TRH (1.0 μg) on gastric contractility was completely abolished by subdiaphragmatic vagotomy. These results suggest that TRH acts within the PVN to stimulate gastric contractility via vagal-dependent pathways.     

Pupillary effects of neurotensin: Structure- activity relationships

We have previously reported that intracameral (I.C.) administration of neurotensin (NT) potently induces a time- and dose-dependent miosis in rabbits. This study was designed to determine structure-function relationships for NT-induced miosis. NT and twelve different fragments and analogs of NT, and the structurally-unrelated peptides beta-endorphin (beta-end), somatostatin (SRIF) and thyrotropin-releasing hormone (TRH) were tested in a dose equimolar to 30 micrograms of NT for their effects on pupillary diameter (PD) in rabbits. In confirmation of previous findings, NT produced significant miosis. Followed in order of duration of effect were D-Trp11-NT, D-Tyr11-NT, the N-terminal fragment NT1-12, [Gln4] - NT and NMe-NT. The N-terminal fragment NT1-8, D-Arg8-NT, and D-Phe11-NT were weakly active. In addition, the initial N-terminal fragment NT1-6 and the C-terminal fragments NT8-13 and NT9-13 did not affect PD. D-Pro10-NT, beta-end, SRIF, and TRH were totally ineffective. The results of this investigation contribute to support a role for NT on regulation of pupillary function, and suggest that the midportion of NT appears to be critical for the expression of NT-induced miosis.     

Microinjection of thyrotropin-releasing hormone analogue into the central nucleus of the amygdala stimulates gastric contractility in rats

The effect on gastric contractility following bilateral microinjection of thyrotropin-releasing hormone (TRH) analog. RX 77368, into the central nucleus of the amygdala was examined in fasted. urethane-anesthetized rats. Extraluminal force transducers were used to measure gastric corpus contractility. Bilateral microinjection of RX 77368 (0.5 μg. 1.0 μg,n = 6 each) stimulated gastric contractility for up to 120 min post-injection,P < 0.05. Gastric contractility was not significantly stimulated by microinjection of 0.1 μg RX 77368. 0.1% bovine serum albumin (BSA) into the central nucleus or RX 77368 (0.5 μg. 1.0 μg) into sites adjacent to the central nucleus. Peak responses (1.0 μg) occurred 40 min post-injection and represented a 16-26-fold increase over basal values. The frequency of gastric contraction waves was attenuated for 0–90 min in rats receiving central amygdaloid microinjection of RX 77368 (0.1. 0.5 or 1.0 μg) versus rats microinjected with the vehicle or RX 77368 into sites adjacent to the central nuclei. The stimulatory effect of RX 77368 (1.0 μg) on gastric contractility was abolished by subdiaphragmatic vagotomy. These results indicate that the TRH analog. RX 77368, acts within the central amygdala to vagally stimulate gastric contractility.     

Postmortem stability and characterization of immunoreactive luteinizing hormone releasing hormone and thyrotropin releasing hormone in human brain tissue

PARKER, C. R., JR. AND J. C. PORTER. Postmortem stability and characterization of immunoreactive luteinizinghormone releasing hormone and thyrotropin releasing hormone in human brain tissue. BRAIN RES. BULL. 8(6) 623–630, 1982.—The content and concentration of immunoreactive luteinizing hormone releasing hormone (LHRH) and of thyrotropin releasing hormone (TRH) were evaluated in hypothalamic tissue of 52 cadavers of adult humans (33 males, 18 to 70 years of age, and 19 females, 17 to 74 years of age). Autopsy was performed between 2.5 and 21 hr after death. When the data were subjected to linear regression analysis, it was found that neither the concentration nor content of LHRH or TRH varied significantly between 2.5 and 21 hr postmortem. The stability of LHRH or TRH in hypothalamic fragments that included the pituitary stalk was similar to the stability of these peptides in hypothalamic fragments that did not include the pituitary stalk. The concentration as well as content of LHRH and TRH in specimens analyzed 2.5 to 12 hr postmortem was similar to that in specimens analyzed 13 to 21 hr postmortem. When aliquots of a homogenate or a synaptosomal fraction of hypothalamic tissue were incubated at 4° or 37°C prior to the analysis of endogenous LHRH and TRH, it was found that the concentration of each peptide remained constant for several hours. However, when synthetic LHRH or TRH was mixed with aliquots of homogenates or subcellular fractions of hypothalamic tissue and incubated at 37°C, each exogenous peptide was rapidly degraded. Based upon the results of gel filtration chromatography, high performance liquid chromatography, biological activity (LHRH), and susceptibility to degradation by serum (TRH), immunoreactive LHRH and TRH in extracts of human brain tissue appeared to be similar to synthetic LHRH and TRH. These findings support the view that, although human brain tissue has the capacity to degrade LHRH and TRH, the endogenous pools of these peptides are sequestered in such a manner that they are stable for several hours in the postmortem human brain. These data are suggestive that brain tissues obtained at autopsy may be useful in the study of peptidergic systems in the human.