salt inducible kinase GHRL effect on appetite is influenced
GHRL effect on appetite is influenced by its dose and route of administration, where central or peripheral administration of GHRL at low doses increases feed intake, via acting on orexigenic hypothalamic neurons, and decreases appetite at high doses in chickens (Jonaidi et al., 2012), quails (Shousha et al., 2005), and some teleost fish (Tinoco et al., 2014). It was suggested that when GHRL injected peripherally in a large dose, it can pass through and the blood-brain barrier and bind with GHSR in hypothalamus resulting in loss of appetite (Shousha et al., 2005). It is therefore possible that under normal condition, the secreted GHRL induces NPY neurons which increase appetite however, when GHRL increases (following injection of a large dose of exogenous GHRL), it may act via CRF neurons which reduce appetite.
Conclusion The main finding of this study was that A239G and G244A SNPs in exon 2 of GHSR were significantly associated with food intake, growth traits (BW, ADG, shank length, keel length, chest circumference), expression level of GHSR, GH (in pituitary gland) and GHRL (in hypothalamus and proventriculus) mRNA, as well as serum level of GHRL and GH in chicken at age from 4 to 16w with superior G allele and GG/GG haplotype. This is the first study to demonstrate that the increased level of the endogenous GHRL, as a result of GHSR SNPs, can induce appetite and increase body gain in chicken and thus the endogenous GHRL is a hunger signal in chickens.
Acknowledgments This study was funded by Research Support Fund, Kafrelsheikh University, Egypt.
Introduction Ghrelin and the functionally antagonistic leptin have been recognized as signaling molecules that are involved in the mechanisms controlling both salt inducible kinase balance and reproduction by acting on various levels of neuroendocrine axis and within the testis , , . Testicular expression of the peptides, their functional receptors and their transcripts were demonstrated in rodents and humans, and some essential data concerning their role in regulatory mechanisms in testis was evaluated , , , , , , , , . When leptin was found to be indispensable for testicular physiology and male fertility, the role of ghrelin in this respect appeared explicitly hard to elucidate. Mice lacking leptin or having mutations within the leptin receptor are infertile and exhibit impaired spermatogenesis, while a lack of ghrelin does not affect male fertility , , , . However, some effects of increased ghrelin level have been observed in the course of experimental hyperghrelinemia in rats, or as a consequence of ghrelin gene overexpression in Prader–Willi syndrome in humans , . An impairment of LH and testosterone secretion, delayed pubertal timing and local defects in spermatogenic cell line maturation were observed in both these cases. Both ghrelin and leptin, as well as their receptors were demonstrated locally in Leydig, Sertoli and spermatogenic cells. The expression of ghrelin was ascribed to Leydig and Sertoli cells , , . In human, ovine and rat testes, ghrelin was also demonstrated immunohistochemically in gametogenic cells , , , and expression of the growth hormone secretagogue receptor type 1a (GHSR-1a) in rat gametogenic cells was documented up to the step of spermiation . The knowledge concerning the expression of the ghrelin receptor in spermatozoa is obscure but expression of the leptin receptor was confirmed in the ejaculated spermatozoa of humans and boars. In humans, the immunoreactivity of the leptin receptor was localized in the sperm tail , . No correlation was found between concentration of leptin in seminal plasma and sperm motility. In vitro recombinant human leptin failed to alter the parameters of sperm motility as well as the percentage of capacitated and acrosome-reacted spermatozoa . Interestingly, leptin receptor expression in boar spermatozoa was localized in the acrosomal region ,  and its activation by leptin resulted in an enhancement of sperm capacitation and motility, stimulation of acrosin and phosphorylation of the BCL2 protein . The presence and role of the ghrelin receptor in spermatozoa as well as its species specificity have been poorly recognized. If ghrelin exerts an action concurrent to leptin, then this justifies searching for the expression and possible functional role of GHSR-1a in rat spermatozoa.