Synthesis and central nervous system actions of thyrotropin-releasing hormone analogs containing a 1-substituted 2-oxoimidazolidine moiety

A series of thyrotropin-releasing hormone (TRH) analogs in which the pyroglutamic acid residue was replaced by (S)-2-oxoimidazolidine-4-carboxylic acid (Oic-OH) and the related derivatives was prepared, and the central nervous system (CNS) actions were examined. Of these, 1-benzyl-Oic-His-Pro-NH2 (2c) showed the most potent activities, which were 1.5-8 times greater than those of TRH. Moreover, the thyrotropin (TSH)-releasing activity of 2c was about 1/16 times weaker than that of TRH.     

Cimetidine effects on prolactin release and production.

The effect of cimetidine 1600 mg. daily for three months on prolactin and related hormones is reported. Basal prolactin levels rose slightly but not significantly. There was no change in basal thyroid and sex hormone levels nor in the prolactin, gonadotrophin or thyrotrophin responses to releasing hormone stimulation. Since intravenous cimetidine induces a transient hyperprolactinemia it appears that cimetidine may facilitate release of prolactin but has no effect on its synthesis.     

Effect of heat stress on plasma concentrations of prolactin and luteinizing hormone in ewes.

Basal concentrations of prolactin but not luteinizing hormone were elevated in ewes by 8--10 h of heat stress given daily during the first 11 days of their oestrous cycle. However, the prolactin and luteinizing hormone responses to thyrotrophin releasing hormone and gonadotrophin releasing hormone were unaffected.     

Effect of long term hormone replacement on plasma prolactin concentrations in women after oophorectomy.

Plasma prolactin concentrations were studied in 88 oophorectomised women who had been receiving mestranol or placebo for three to 11 years. Thirty one of them were also studied under basal conditions and by tests with thyrotrophin releasing hormone. Under basal conditions the mean prolactin concentration was higher in the oestrogen treated group but under non-rested, clinic conditions the difference was lost because of a rise in prolactin value in the placebo group only. Hence the groups showed a different prolactin response to the mild stress of clinic attendance but the same proportionate responsiveness to thyrotrophin releasing hormone. The data suggest that long term hormone replacement has no significant effect on circulating prolactin concentrations under non-rested, everyday conditions and that the prolactin stimulating effects of minor stress and oestrogen may share a similar mechanism.     

Effect of luliberin on the activities of mitochondrial respiratory enzymes]

Luliberin, a luteinizing hormone-releasing hormone, was shown to inhibit the respiratory enzymes of rat liver mitochondria and submitochondrial particles prepared from beef heart mitochondria. At the hormone concentration of 8.10(-6) M the NADH-oxidase activity of the submitochondrial particles was inhibited by 50%. The fragments of the hormone and its analogs and pyroglutamic acid, oxytocin and bradikinin possessed practically no inhibiting effects. In the case of submitochondrial particles the inhibition was only observed in the presence of Ca2+ and was significantly decreased after addition of bovine serum albumin and phospholipase inhibitors -- butacaine and dicaine. It is assumed that the effect of luliberin on the respiratory chain is mediated through mitochondrial phospholipase.     

Synthesis and biology of new thyrotropin-releasing hormone (TRH) analogues.

We report synthesis and biological activities of several thyrotropin-releasing hormone (TRH) analogues in which the N-terminal pyroglutamic acid residue has been replaced with various carboxylic acids and the central histidine is modified with substituted-imidazole derivatives.     

2-Diazohistidinyl thyrotropin-Releasing Hormone (TRH) A Photosensitive TRH Analog

Abstract

We have synthesized a new thyrotropin releasing hormone (TRH) analog, pGlu-2-diazo-His-Pro-NH₂ 5, which is a potential photoaffinity label for the TRH receptor. Its precursor, pGlu-2–amino-His-Pro-NH₂ 4, has been synthesized through successive coupling of a 2–aminohistidine derivative 1 with proline and pyroglutamic acid derivatives. Diazotization of the fully deprotected tripeptide 4 gave the photoactivatable TRH analog 5.

Compounds 4 and 5 exhibit IC₅₀ values of 2 and 8 μM respectively, to be compared to the 0.02 μM value for native TRH.     

Coordination ability of the thyrotropin releasing factor, l-pyroglutamyl-l-histidyl-l-prolinamide(TRF).III. Cu(II) and Ni(II) complexes with TRF and its di- and tripeptide analogues

The results are reported of a spectroscopic and potentiometric study of the copper(II) and nickel(II) complexes of the thyrotropin releasing factor (L-pyroglutamyl-L-histidyl-L-prolinamide, TRF) and some of its di- and tripeptide analogues Spectroscopic techniques used include absorption, circular dichroism and electron paramagnetic resonance spectroscopy TRF and pyroglutamyl-histidine behave similarly. At low pH the metal ions coordinate to the imidazole nitrogen and then cause the ionization of the amide protons of both the peptide linkage and the pyroglutamic acid with equal ease. Hence the concentration of MH_?1 L species is always very low. The C-terminal proline amide residue plays an insignificant role in the complex formation Replacement of pyroglutamic acid with picolinic acid in the hormone molecule causes a major change in the structures of its complexes. The dipeptide analogue, Pic-His. forms dimeric species with Cu(II) that are not found in Cu(II) Pyr-His orCu(II) TRF solutions The introduction of tyrosine residue in the TRF sequence in place of histidine can, in some cases, lead to the direct involvement of proline amide in the binding of metal ions, e.g. , Ni(II) Pyr-Tyr-Pro-NH₂     

Improved solid phase synthesis of luteinizing hormone releasing hormone analogues using 9-fluorenylmethyloxycarbonyl amino acid active esters and catalytic transfer hydrogenation with minimal side-chain protection and their biological activities

Using mainly 9-fluorenylmethyloxycarbonyl amino acid 2, 4, 5-trichlorophenyl esters in the presence of 1-hydroxybenzotriazole and the solid supportp-alkoxybenzyl alcohol resin, synthesis of luteinizing hormone releasing hormone analogues was carried out with minimal side-chain protection. Catalytic transfer hydrogenation was employed for removal of NO₂ and Z-groups from Arg and < Glu respectively avoiding the use of HF and this led to good yields. An aromatic, hydrophilic amino acid, D-(p-hydroxyphenyl) glycine was incorporated into luteinizing hormone releasing hormone molecule along with other modifications. The agonistic as well as antagonistic activities of all the peptides have been studied     

Evidence for a hypothalamic disturbance in cyclical oedema.

Fourteen women with cyclical oedema and six healthy female controls were investigated by use of a test in which thyrotrophin releasing hormone and luteinising hormone releasing hormone were given. Significant differences in the responses of prolactin, luteinising hormone, and follicle stimulating hormone were observed in the patients. These findings suggest that there may be a hitherto unrecognised hypothalamic defect in cyclical oedema that may account for some of the previously unexplained clinical features and lead to a more rational therapeutic approach in the management of the disorder.     

The failure of prolactin to initiate lactogenesis in the ewe.

Infusion of exogenous prolactin (NIH-P-S11) at 1 mg/h for 10 h into ewes pretreated for 30 days with oestradiol benzoate and progesterone was unable to initiate milk secretion. Similarly primed ewes injected with 10 microgram thyrotrophin releasing hormone also failed to lactate but all ewes injected with dexamethasone (10 mg daily for 5 days) after oestrogen plus progesterone treatment secreted copious quantities of milk. The results suggest that prolactin, itself, is not capable of initiating lactogenesis in the ewe.     

Development of hypothalamic control over thyrotropin secretion during human prenatal life]

It was shown in the tissue culture experiments that the human hypophysis secreted autonomously the thyrotrophin during the last three fourths of the prenatal life. The intensity of secretion is the highest in the end of the first third of this period, then it decreases, but during the last third it increases reliably again. During the second half of development the level of thyrotrophin in female foetuses in reliably higher than in the male ones. In the beginning of the second third of prenatal life, the hypothalamic factors decrease the autonomous thyrotrophin secretion twice in foetuses of both the sexes. In the end of the second third, sexual differences appear in their effect; they decrease reliably the autonomous thyrotrophin secretion in the male foetuses, whereas no such effect is observed in the female ones. The stimulating effect of the hypothalamic thyrotrophin releasing hormone manifests itself during the last third of prenatal life in foetuses of both the sexes. During the second half of prenatal life, the thyrotrophin concentration in blood of female foetuses is also reliably higher than in male foetuses. There is a positive correlation in female foetuses between the thyrotrophin concentration in blood and the level of hypophysial secretion under the effect of hypothalamic factors. Thyrotrophin is found in the cranial fluid of foetuses. In some cases its concentration in the cranial fluid is higher than in the blood. No correlation was found between the levels of the hormone in fluid and blood in female foetuses; a positive correlation was found in male foteuses.     

Biological activities of thionated thyrotropin-releasing hormone analogs.

Analogs of thyrotropin-releasing hormone (Glp-His-Pro-NH2, TRH) have been prepared which contain thioamide moieties in the pyroglutamic acid ring, the carboxyamide proline terminus, and in both positions (dithio). These compounds have been tested for TSH-releasing activities (in vitro and in vivo), and for binding to TRH receptors in rat pituitary and cortex. The monothionated analogs showed no significant differences in TSH-releasing potency from TRH either in vitro or in vivo. However, with two thioamide replacements the potency decreases about 50%. Significantly, in terms of receptor selectivity, thionation has resulted in differentiation between brain receptors (pituitary and cortex). The Pro psi[CSNH2] and dithio analogs were more selective (higher affinity to pituitary receptors) than the parent hormone, while the analog containing a thioamide replacement in the pyroglutamyl ring had lower affinity and was not selective. These results suggest that the subtle exchange of sulphur for oxygen can have an important impact on both receptor selectivity and affinity within a biologically active peptide.     

Human erythrocyte glucose 6-phosphate dehydrogenase. Content of bound coenzyme

A series of peptide analogs of luteinizing hormone releasing hormone (LH-RH), altered at position 6 and 10, was synthesized and evaluated $\text{in vivo}$ for the ability to induce ovulation in the diestrous rat and $\text{in vitro}$ for ability to release pituitary luteinizing hormone and follicle stimulating hormone. All the analogs with D-amino acid substitutions at position 6, even those with large bulky side chain, exhibited an amazingly high potency compared with the parent hormone, LH-RH. On the basis of the biological activities, structure-activity relationships in the central part of this molecule were discussed in detail.     

Growth hormone release inhibiting hormone: actions on thyrotrophin and prolactin secretion after thyrotrophinreleasing hormone.

The hypothalamic tetradecapeptide growth hormone release inhibiting hormone (GH-RIH) blocked the thyrotrophin response to thyrotrophin-releasing hormone (TRH) in normal people and in patients with primary hypothyroidism. This inhibition was dose related. The TRH-induced prolactin release was not affected by GH-RIH. This dissociation of the thyrotrophin and prolactin responses to TRH by GH-RIH suggests that there are different mechanisms for release of thyrotrophin and prolactin and that only the former is affected by GH-RIH.     

Conformational properties of 2,3-methanopyroglutamic acid in peptides: NMR and x-ray diffraction studies

The effects of replacing L-pyroglutamic acid with the cyclopropane analogue 2,3-methanopyroglutamic acid (2,3-MeGlp) on conformation and enzymatic stability have been investigated in 2,3-MeGlp-NHMe and the novel thyrotropin releasing hormone (TRH) analogue [2,3-MeGlp1]-TRH by x-ray diffraction and nmr. While 2,3-MeGlp-NHMe adopts a folded conformation (small psi angle) in the solid state, several conformations are available to the molecule in solution. 1H-nmr of the diastereomeric mixture [(+/- )-2,3-MeGlp1]-TRH indicates a close orientation of the pyrrolidone and imidazole rings. The 2,3-MeGlp-His amide bond is considerably more stable to pyroglutamate aminopeptidase than the Glp-His bond in TRH.     

Stimulation of growth hormone release in dwarf and normal chickens by thyrotrophin releasing hormone (TRH) or human pancreatic growth hormone releasing factor (hpGRF)

The effect of thyrotrophin releasing hormone (TRH) or human pancreatic growth hormone releasing factor (hpGRF) on growth hormone (GH) release was studied in both dwarf and normal Rhode Island Red chickens with a similar genotype except for a sex-linked dw gene. Both TRH (10 micrograms/kg) and hpGRF (20 micrograms/kg) injections stimulated plasma GH release within 15 min in young and adult chickens. The increase in GH release was higher in young cockerels than that in adult chickens. The age-related decline in the response to TRH stimulation was observed in both strains, while hpGRF was a still potent GH-releaser in adult chickens. The maximal and long acting response was observed in young dwarf chickens, suggesting differences in GH pools releasable by TRH and GRF in the anterior pituitary gland. The pituitary gland was stimulated directly by perifusion with hpGRF (1 microgram/ml and 10 micrograms/ml) or TRH (1 microgram/ml). Repeated perifusion of GRF at 40 min intervals blunted further increase in GH release, but successive perifusion with TRH stimulated GH release. The results suggest the possibility that desensitization to the effects of hpGRF occurs in vitro and that the extent of response depends on the number of receptors for hpGRF or TRH and/or the amount of GH stored in the pituitary gland.     

生长激素释放肽的合成及促生长活性

用固相多肽合成法合成了生长激素释放肽(GHRP),这是一种含D-型氨基酸的外源性激素,具有促进脑下垂体分泌生长激素功能的人工合成六肽,其氨基酸序列为His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂.观察了使用不同剂量的GHRP对不同日龄小鼠的促生长效应,当使用最佳剂量(1000μg/kg)时,可使25日龄小鼠体重较对照组增加14.8%,同时发现鼠龄越小对GHRP越敏感,当使用剂量高达10mg/kg时仍然安全无毒.     

Intestinal transport of TRH analogs through PepT1: the role of in silico and in vitro modeling

The present study involves molecular docking, molecular dynamics (MD) simulation studies, and Caco‐2 cell monolayer permeability assay to investigate the effect of structural modifications on PepT1‐mediated transport of thyrotropin releasing hormone (TRH) analogs. Molecular docking of four TRH analogs was performed using a homology model of human PepT1 followed by subsequent MD simulation studies. Caco‐2 cell monolayer permeability studies of four TRH analogs were performed at apical to basolateral and basolateral to apical directions. Inhibition experiments were carried out using Gly‐Sar, a typical PepT1 substrate, to confirm the PepT1‐mediated transport mechanism of TRH analogs. P_app of the four analogs follows the order: NP‐1894 < NP‐2378 < NP‐1896 < NP‐1895. Higher absorptive transport was observed in the case of TRH analogs, indicating the possibility of a carrier‐mediated transport mechanism. Further, the significant inhibition of the uptake of Gly‐Sar by TRH analogs confirmed the PepT1‐mediated transport mechanism. Glide docking scores of all the four analogues were in good agreement with their transport rates, suggesting the role of substrate binding affinity in the PepT1‐mediated transport of TRH analogs. MD simulation studies revealed that the polar interactions with amino acid residues present in the active site are primarily responsible for substrate binding, and a downward trend was observed with the increase in bulkiness at the N‐histidyl moiety of TRH analogs. Copyright © 2014 John Wiley & Sons, Ltd.     

Electroconvulsive seizure-induced gene expression profile of the hippocampus dentate gyrus granule cell layer

Electroconvulsive shock (ECS) is the most effective treatment for depression, but the mechanism underlying the therapeutic action of this treatment is still unknown. To better understand the molecular changes that may be necessary for the clinical effectiveness of ECS we have combined the technologies of gene expression profiling using cDNA microarrays with T7-based RNA amplification and laser microdissection to identify regulated genes in the dentate gyrus granule cell layer of the hippocampus. We have identified genes previously reported to be up-regulated following ECS, including brain-derived neurotrophic factor, neuropeptide Y, and thyrotrophin releasing hormone, as well as several novel genes. Notably, we have identified additional genes that are known to be involved in neuroprotection, such as growth arrest DNA damage inducible beta (Gadd45beta), and the excitatory amino acid transporter-1 (EAAC1/Slc1A1). In addition, via in situ hybridization we show that EAAC1 is specifically up-regulated in the dentate gyrus, but not in other hippocampal subfields. This study demonstrates the utility of microarray analysis of microdissected subregions of limbic brain regions and identifies novel ECS-regulated genes.