Ghrelex (D-Lys³ GHRP-6)

Ghrelex (D-Lys³ GHRP-6)

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Product Code: GLHS
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Description

Ghrelex or D-Lys³ GHRP-6, also called [D-Lys3]GHRP-6, is a synthetic growth-hormone secretagogue receptor (GHS-R) antagonist that is structurally an analog of growth hormone-releasing peptide 6 (GHRP-6). Like GHRP-6, [D-Lys3]GHRP-6 is a hexapeptide. Compared to the structure of GHRP-6, the structure of [D-Lys3]GHRP-6 (His-Trp-Lys-Trp-Phe-Lys-NH2) contains a substituted D-lysine. Ghrelex is most often used as a control in studies examining the role or effects of ghrelin or ghrelin analogs, and as a way of characterizing GHS-R involvement in physiological processes, but has also been shown in early trials to reduce alcohol preference and also to hold some potential for treating obesity[1][2]. Like ghrelin, D-Lys³ GHRP-6 exerts its effects on the enteroinsular axis, both centrally and peripherally.

Maletínská et al (2011) found that, through ghrelin antagonism, [D-Lys3]GHRP-6 reduced food intake, body-weight, and adiposity:

Ghrelin receptor antagonist [D-Lys(3)]GHRP-6 after seven days of subcutaneous treatment markedly decreased food intake in OVX mice fed both HF and standard diets; furthermore, it reduced body weight and blood glucose, insulin and leptin, and increased β-hydroxybutyrate level and uncoupling-protein-1 mRNA in brown adipose tissue. Pair-feeding revealed that effect of [D-Lys(3)]GHRP-6 was primary anorexigenic. Estrogen supplementation reduced anorexigenic effects of [D-Lys(3)]GHRP-6. OVX [D-Lys(3)]GHRP-6 treatment in mice on HF diet resulted in markedly increased circulating level and liver expression of a major metabolic regulator, fibroblast growth factor 21. Our data suggest that ghrelin antagonists could be especially beneficial in individuals with common obesity combined with estrogen deficiency[2]

Kaur and Ryabinin (2010) explored the effect of ghrelin antagonism on alcohol intake and a number of related measures:

In Experiment 1, D-Lys3-GHRP-6 reduced preference to alcohol and in a follow-up experiment (Experiment 2) also dramatically reduced alcohol intake when compared to saline-treated mice. The resulting blood ethanol concentrations were lower in mice treated with the ghrelin receptor antagonist. Immunohistochemistry for c-Fos showed fewer immunopositive cells in the pIIIu of the antagonist-treated mice but no difference was seen in the VTA or Arc. In Experiment 3, D-Lys3-GHRP-6 reduced the induction of c-Fos by intraperitoneal ethanol in the pIIIu but had no effect in the VTA. In the Arc, there was a significant increase in the number of c-Fos immunopositive cells after D-Lys3-GHRP-6 administration, but the antagonist had no effect on ethanol-induced expression of c-Fos. D-Lys3-GHRP-6-pretreatment also did not affect the blood ethanol concentrations observed after a systemic injection of ethanol when compared to saline-pretreated mice (Experiment 4).[3]

Vlasova, Järvinen, and Herzig find that “the peripheral injection of ghrelin antagonist increases arterial pressure and heart rate, at least in part, through the activation of the sympathetic nervous system”[4].

In a 2014 trial Pirnik et al deciphered a relationship between the ghrelin pathway, the enteroinsular axis, and catecholamine biosynthesis:

GHS-R antagonist also significantly increased TH neurons activation after GHS-R agonist although this effect was less powerful in HFD [high-fat diet] mice. This is the first study demonstrating response of local ARC TH neurons to peripherally applied GHS-R agonist and antagonist. The present data point out that the response of TH neurons to GHS-R agonist and antagonist is different in normal and DIO [diet-induced obesity] mice and extend our knowledge about the further ARC neuronal phenotype responding to peripheral ghrelin[5]

Tyrosine hydroxylase is involved in the synthesis of dopamine.

Citations
[1]Kaur S, Ryabinin AE. Ghrelin receptor antagonism decreases alcohol consumption and activation of perioculomotor urocortin-containing neurons. Alcohol Clin Exp Res. 2010 Sep 1;34(9):1525-34.
[2]Maletínská L, Matyšková R, Maixnerová J, Sýkora D, Pýchová M, Spolcová A, Blechová M, Drápalová J, Lacinová Z, Haluzík M, Zelezná B. The Peptidic GHS-R antagonist [D-Lys(3)]GHRP-6 markedly improves adiposity and related metabolic abnormalities in a mouse model of postmenopausal obesity. Mol Cell Endocrinol. 2011 Aug 22;343(1-2):55-62.
[3]Kaur S, Ryabinin AE. Ghrelin receptor antagonism decreases alcohol consumption and activation of perioculomotor urocortin-containing neurons. Alcohol Clin Exp Res. 2010 Sep 1;34(9):1525-34.
[4]Vlasova MA, Järvinen K, Herzig KH..Cardiovascular effects of ghrelin antagonist in conscious rats. Regul Pept. 2009 Aug 7;156(1-3):72-6.
[5]Pirnik Z, Majercikova Z, Holubova M, Pirnik R, Zelezna B, Maletinska L, Kiss A. Effect of ghrelin receptor agonist and antagonist on the activity of arcuate nucleus tyrosine hydroxylase containing neurons in C57BL/6 male mice exposed to normal or high fat diet. J Physiol Pharmacol. 2014 Aug;65(4):477-86.

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