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Peptides
Published in Linda M. Castell, Samantha J. Stear (Nottingham), Louise M. Burke, Nutritional Supplements in Sport, Exercise and Health, 2015
Technically speaking, proteins are long chains of amino acids, while peptides are shorter chains of amino acids that can be produced synthetically, endogenously, or derived from food. It has been suggested that some naturally occurring food-derived peptides, such as the peptides that reside in milk proteins (such as whey and casein) and become active during proteolytic digestion, may offer health benefits (improved cardiovascular, digestive and immune function) independently of their role as a dietary source of amino acids (Nagpal et al., 2011). More evidence is required to support or refute this claim. These peptides are not the concern of the sport authorities involved in the maintenance of the integrity in professional sport. Rather, attention has been focused on the use by athletes of a range of synthetic peptides which have apparently become commercially available (often via internet sites) under the guise of supplements. These products, which can be administered via a variety of methods (orally, intravenous, intranasal or transdermal cream, etc.), may exert anabolic effects and/or serve as masking agents for other drugs. A particular sub-set, the synthetic growth hormone-releasing peptides (GHRP) which include GHRP-6, hexarelin or CJC-1295, have been demonstrated to stimulate the release of GH from the pituitary gland thereby enhancing its endogenous production (Ghigo et al., 1994; Teichman et al., 2006). The synthetic GHRPs were specifically developed and intended for medical use in patients with intact or impaired pituitary function to mimic the pulsatile nature of endogenous GH release (Teichman et al., 2006). In the case of CJC-1295, a single injection of this peptide has been demonstrated to induce an increase in serum GH concentrations that seems to persist for ~two weeks in healthy adults (Teichman et al., 2006). GH therapy, however, is often administered in a single daily dose and results in a robust (supraphysiological) increase in systemic concentrations of GH that wanes over time.
Effect of feeding regimen on circadian activity rhythms of food anticipatory by ghrelin hormone in a pig model
Published in Nutritional Neuroscience, 2023
He Zhang, Xiaoxi Yan, Ailian Lin, Pengke Xia, Menglan Jia, Yong Su
Ghrelin modified the expression of the clock gene in embryonic mouse hypothalamus neuron cells in vitro (P < .05) (Figure 9(A–F)). All the clock genes studied were induced by 10 nM-1μM ghrelin post-treatment. The highest induction was found for PER1 transcripts, which increased around 4-fold at 0.5 h and 1 h post-treatment, while the induction of CRY1 expression was smaller (under 2-fold). All the ghrelin-evoked up-regulation of clock gene expression observed at 0.5 h and 1 h diminished after 2 h of ghrelin exposure and even disappeared in the case of BMAL1, CLOCK, and PER1. The ghrelin receptor antagonist, [D-Lys3]-GHRP-6 was used to test the specificity of the ghrelin-evoked induction of clock gene expression. The presence of the antagonist in the culture medium did not modify the expression of the clock gene by itself, levels of all clock genes were modified by the antagonist after a 1 h incubation. Pre-incubation (15 min) of N38 cells with the [D-Lys3]-GHRP-6 abolished or significantly down-regulated the stimulatory effect of ghrelin on all clock gene expression (P < .05) (Figure 10(A)). Moreover, [D-Lys3]-GHRP-6 administration for 1 h decreased the GHS-R1a, p-CaMKII, and p-CREB protein levels (P < .05) (Figure 10(C)).
Unacylated ghrelin stimulates steroidogenesis in lean rats and reverses reproductive dysfunction in high fat diet-fed rats
Published in Systems Biology in Reproductive Medicine, 2019
Interestingly, BMI is positively correlated with circulatory AG, and a high ratio of circulatory AG/UAG was shown in obese children or adults (St-Pierre et al. 2007; Pacifico et al. 2009; Rodríguez et al. 2009). Also, GHS-Ra1 protein levels were significantly increased in ob/ob mice (Zhu et al. 2013). Concomitant with its adipogenic effect, in vitro and in vivo evidences in males have shown that AG delays puberty, impairs reproductive function and reduces testosterone secretion in several ways including inhibition of Leydig cells proliferation, suppression of steroidogenic enzymes, suppression of LH and follicular stimulating hormone (FSH) release and induction of germ cell apoptosis (reviewed in Alves et al. 2016). On the contrary, inhibition of ghrelin signaling by GHS-R-1a [D-Lys-3]-GHRP-6 (D-GHRP), a specific GHS-R1a antagonist, restored androgen synthesis, reduced germ cell apoptosis, and improved sperm production in ob/ob mice (Zhu et al. 2013).
The autoimmune basis of hypopituitarism in traumatic brain injury: fiction or reality?
Published in British Journal of Neurosurgery, 2019
Viraat Harsh, Sukriti Jha, Hitesh Kumar, Anil Kumar
In continuation of this study, Tanriverdi and de Bellis11 in 2008 sought to investigate the presence of APAs in these patients three years after TBI. Indirect immunofluorescence (IIF) was used on cryostat sections of young baboon's pituitary glands for the detection of APAs although other techniques like immunoblotting, enzyme linked immuno-sorbent assay (ELISA), fluid phase radioassay and antigen assay have also been described.4 A patient was said to be APA positive if his serum titre measured more than 1/8. It was seen that 13 out of 29 patients (44.8%) were APA positive while none of the controls showed any presence of APAs. Of these 13, seven were weakly (titre 1/8) while six were strongly positive (titre 1/64-1/128). Pituitary dysfunction was observed in eight out of 29 patients. Six of them were APA positive while two were APA negative. All the strongly APA positives presented with pituitary dysfunction, mostly with isolated GHD while none of those weakly positive for APAs showed any hormonal imbalance. Those APA positive, had higher rates of pituitary dysfunction, 46% as compared to APA negatives (12.5%), the odds ratio (OR) being 2.25. Furthermore, a significant positive correlation (r = 0.74, p = .004) between APA titer ratio and peak GH response to GHRH + GH related peptide (GHRP)-6 test was observed which implies that high APA titers were associated with low GH response to GHRH + GHRP-6 test.