Isolation and structural characterization of chicken hypothalamic luteinizing hormone releasing hormone

Studies on partially purified chicken hypothalamic luteinizing hormone releasing hormone (LHRH) utilizing chromatography, radioimmunoassay with region-specific antisera, enzymic inactivation, and chemical modification established that the peptide is structurally different from mammalian hypothalamic LHRH. These studies demonstrated that arginine in position 8 is substituted by a neutral amino acid. On the basis of conformational criteria and evolutionary probability of amino acid interchange for arginine, the most likely substitution was glutamine. We therefore synthesized [Gln8]-LHRH and established that it had identical chromatographic, immunologic, and biological properties to the natural chicken peptide. In concurrent studies, purification of 17 micrograms of an LHRH from 249,000 chicken hypothalami was achieved using acetic acid extraction, immuno-affinity chromatography, and cation exchange and reverse phase high performance liquid chromatography. Amino acid composition and sequence analyses confirmed the structure of this form of chicken LHRH as pGlu-His-Trp-Ser-Tyr-Gly-Leu-Gln-Pro-Gly-NH2.     

Effects of ethanol on rat hypothalamic luteinizing hormone releasing hormone. A study utilizing radioimmunoassay

To further understand the mechanism of action by which ethanol (ETOH) decreases plasma luteinizing hormone (LH) levels, the effects of multiple i.p. injections of EOH (1.0--1.5 g/kg) or saline on hypothalamic luteinizing hormone releasing hormone (LHRH) and plasma LH concentrations were evaluated in intact and castrate male rats. After injections, animals were decapitated, brains rapidly removed, and blocks containing the hypothalamus [with median eminence (ME)] were isolated. Hypothalami were subjected to acetic acid extraction and LHRH content quantitated via radioimmunoassay (RIA). Hypothalamic LHRH was found to be inversely correlated with plasma LH. In response to castration, both saline and ETOH-treated rats showed a decrease in hypothalamic LHRH content with a concomitant increase in plasma LH; however, the ETOH-treated animals retained significantly greater concentrations of LHRH and showed significantly lower plasma LH levels when compared to saline-treated controls. Likewise, ETOH-treated intact animals showed significant increases in LHRH content, with LH levels remaining significantly lower than the saline-treated intact controls. Thus, these data from both intact and castrate rats provide evidence to support the hypothesis that alcohol-induced decreases in LH levels are due to a diminished release rate of hypothalamic LHRH.     

Adrenal luteinizing hormone releasing hormone receptors.

Paraffin sections of mouse adrenals processed with antiserum to luteinizing hormone-releasing hormone (LHRH) in the unlabeled antibody enzyme method reveal moderate staining in the cytoplasm of cells of zona fasciculata and reticularis. The stain is intensified upon pretreatment of sections with LHRH. Pretreated sections processed with solid phase immunoabsorbed LHRH are unstained. Analogues of LHRH deficient in the C-terminal glycine amide inhibit staining, while analogues deficient in the N-terminal pyroglutamic acid have no effect. It is concluded that the adrenal contains receptors for a ligand resembling LHRH in receptor and immunoreactivity. The possibility is considered that the ligand may be an inhibitor of pineal origin.     

Human placental receptors for luteinizing hormone releasing hormone

The GTPase activity of the tubulin-colchicine complex has been studied at different tubulin-colchicine concentrations. The specific activity was found to decrease at low concentrations. Several hypothesis accounting for this observation have been discarded, and the activation via collisions between two molecules of tubulin has been considered as a possible model explaining the origin and observed concentration dependence of the GTPase activity. The activation of tubulin-colchicine by unliganded tubulin or tubulin-podophyllotoxin has been investigated within this model which emphasizes the connection between some specific tubulin-tubulin interactions and the conformation of the exchangeable nucleotide site on tubulin.     

Circular dichroism study of the solution conformation of luteinizing hormone releasing hormone.

A systematic investigation has been made into the circular dichroic behavior of luteinizing hormone releasing hormone and its peptide fragments and deletion analogues. The results are interpreted to mean that the hormone exists in solution as an ensemble of conformers with different sensitivities to temperature and solvent composition. The far-ultraviolet circular dichroic spectra exhibited by the hormone under different experimental conditions can be simulated satisfactorily by the weighted addition of the spectra of its aliphatic- and aromatic-containing halves. However, the structure of the hormone is not simply the sum of its halves, since some conformational feature of the intact molecule perturbs the near-ultraviolet circular dichroism of its aromatic residues.     

Changes in prolactin levels caused by luteinizing hormone releasing hormone

The acute effects of luteinizing hormone releasing hormone (LHRH) on the release of prolactin (PRL) were investigated in 12 normal cycling women and 42 women with various menstrual disorders. LHRH (100 micrograms) was bolusly injected intramuscularly and PRL levels were measured immediately before the injection and at 30 minutes and 60 minutes after the injection. LHRH elicited an increase of more than 25% in PRL levels in 15 cases (27.8%) at both 30 minutes and 60 minutes after the injection, whereas PRL levels were decreased by more than 25% in 7 cases (13.0%). The PRL response to LHRH seemed to be related to basal PRL levels. Especially when the PRL concentration was 20 ng/ml or more, LHRH decreased PRL levels in 7 cases out of 16. On the other hand, LHRH increased PRL levels in the majority of cases with a PRL concentration less than 20 ng/ml. In conclusion, the LHRH injection occasionally alters PRL levels in either a positive or negative manner, depending upon the basal PRL levels.     

On the existence and separation of the follicle stimulating hormone releasing hormone from the luteinizing hormone releasing hormone.

Porcine hypothalamic fragments were extracted by 2M AcOH at 4°C, and the extractives were subsequently processed in the presence of one protease inhibitor and one anti-oxidant. Gel filtration was performed on Bio-Gel P-2, and supplementary [³H]-LHRH and [¹⁴C]- 3H]-LHRH, and was differentiated from [¹⁴C]- 相似文献   

Effects of luteinizing hormone releasing hormone on gonadotrophins in the hamster

The changes in serum gonadotrophins in male hamsters following one injection of 15 μg luteinizing hormone releasing hormone (LHRH) (Group A) were compared with those following the last injection of LHRH in animals receiving an injection approximately every 12 hr for 4 days (Group B) or 12 days (Group C). Peak follicle stimulating hormone (FSH) levels (ng/ml) were 1776±218 (Group A), 2904±346 (Group B), and 4336±449 (Group C). Peak luteinizing hormone (LH) values (ng/ml) were 1352±80 (Group A), 410±12 (Group B), and 498±53 (Group C). Serum FSH:LH ratios, calculated from the concentrations measured 16 hr after the last LHRH injections, were higher in Groups B and C than in Group A. Similar injections of LHRH (100 ng or 15 μg/injection) for 6 days elevated the serum FSH:LH ratio in intact males. Five such LHRH injections (100 ng/injection) blunted the rise in serum LH in orchidectomized hamsters. Direct effects of LHRH on gonadotrophin secretory dynamics or altered brain-pituitary-testicular interactions may alter the ratio of FSH to LH in the hamster.     

Effective antagonists of luteinizing hormone releasing hormone modified at position one

Summary The amino acid, D-2-naphthylalanine, has been used by many investigators as a substituent for position one of antagonists of LHRH. We have newly designed substituents for position one in which the carboxy groups of 2-naphthoic acid, 3-quinoline- and 2-quinoxaline-carboxylic acids are linked to the five amino acids, DAla, DThr, DNVal, DSer, and Gly. The substituents in positions 2–10 were DpClPhe², DPal³, Ser⁴, PicLys⁵, DPicLys⁶, Leu⁷, ILys⁸, Pro⁹, DAlaNH₂ ¹⁰.Remarkably, DThr, acylated on the amino group by 3-quinolinecarboxylic acid or by 3-quinoxalinecarboxylic acid, and introduced into position one of a relatively potent antagonist, gave a new class of antagonists of LHRH, which released as little histamine as yet recorded, and yet possessed reasonable antiovulatory activity and greatly improved solubility.These structure-activity results advance the basic knowledge of understanding the structural features of such decapeptides which cause antiovulatory activity and histamine release.Abbreviations ILys N -isopropyllysine; - 1-Nal 3-(1-naphthyl)alanine - 2-Nal 3-(2-naphthyl)alanine - Nap 2-naphthoic acids - NicLys N -nicotinoyllysine; - Pal 3-(3-pyridyl)alanine - pClPhe 3-(4-chlorophenyl)alanine - PicLys N -picolinoyllysine - c-PzACAla cis-3-(4-pyrazinylcarbonylaminocyclohexyl) alanine - 3-Qal 3-(3-quinolyl)alanine - Qui 3-quinolinecarboxylic acid - Qux 2-quinoxalinecarboxylic acid     

The effects of luteinizing hormone releasing hormone (LH-RH) in pregnant rats. I. Postnidatory effects.

The effects of LH-RH on pregnancy in rats were investigated. A single 500 mcg injection of LH-RH on Days 9, 10, or 11 of pregnancy terminated pregnancy, whereas injection on Days 6-8 or 13-16 had little or no effect. The ED 50 on Day 10 for b.i.d. administration was 150 mcg and 550 mcg for a single injection. Administration on Day 9 was followed by a decrease in circulating progesterone levels on Days 10 and 11. The administration of large doses of progesterone reversed the effects of LH-RH administration on Days 7-12. Treatment with estradiol-17beta did not potentiate the effect of progesterone, but appeared to slightly retard fetal resorption when administered alone. The results suggest that the antifertility effect of LH-RH is mediated via functional luteolysis.     

Luteinizing hormone releasing hormone mediates naloxone's effects on serum luteinizing hormone levels in normal and morphine-sensitized male rats

Naloxone produces large increases in serum luteinizing hormone (LH) levels in normal males and females, supporting a role for endogenous opioids (EOP) in the tonic inhibition of LH. Since the antagonist apparently exerts no important effects on the pituitary, the reasonable assumption has been made that it elevates gonadotropin levels by affecting the release of LH-releasing hormone (LHRH) from the hypothalamus. However, at present there is no direct in vivo evidence supporting this widely-held view. In an attempt to directly demonstrate that naloxone increases the secretion of LHRH, and thereby elevates serum LH levels, we examined whether a potent synthetic antagonist of LHRH ( [D-p Glu1, D-Phe2, D-Trp3,6]-LHRH, GPT-LHRH) blocked the effects of naloxone in male rats with a normal response to naloxone and in those with a markedly enhanced sensitivity to the drug induced by a brief period of morphine pellet implantation. Our results demonstrated that GT-LHRH antagonized equipotent doses of LHRH (100 ng/kg) and naloxone (0.5 mg/kg) over a similar time course with approximately the same AD50. Most importantly, however, we showed that the GPT-LHRH produced equivalent, parallel shifts to the right in the dose-response curves for LHRH and naloxone, indicative of competitive inhibition. We also found that GPT-LHRH completely abolished the enhanced response to naloxone's effects on LH which occurs in morphine-pretreated rats. Since we observed no competition between LHRH and naloxone for their binding sites in pituitary or brain, the only viable interpretation of our results is that naloxone increases LH by inducing the release of LHRH.