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Orexin A and its role in the regulation of the hypothalamo-pituitary axes in the rat
Authors:Martyńska Lidia  Polkowska Jolanta  Wolińska-Witort Ewa  Chmielowska Magdalena  Wasilewska-Dziubińska Elzbieta  Bik Wojciech  Baranowska Bogusława
Affiliation:Department of Neuroendocrinology, Medical Centre of Postgraduate Education, Marymoncka 99/103, 01-813 Warsaw, Poland. zaklad.neuroendokrynologii@cmkp.edu.pl
Abstract:Orexin A (OxA), a recently discovered neuropeptide, is synthesized mainly by neurons located in the posterolateral hypothalamus and is a 33 amino acid peptide with N-terminal pyroglutamyl residue and two inter-chain disulfide bonds. It is a potent agonist for both the orexin-1 (OxR1) and orexin-2 (OxR2) receptors. Orexin A and its receptors are widely distributed in the central nervous system (CNS) and peripheral organs suggesting the pleiotropic functions of this peptide. Orexin A is involved in food intake and energy expenditure in many species, but also plays an important role in the regulation of the hypothalamo-pituitary axes. The role of orexin A in the regulation of the hypothalamo-pituitary-adrenal, -thyroid, -somatotropic, and -gonadal axes has been inadequately investigated. Orexinergic fibres project to the septal-preoptic and arcuate nucleus-median eminence regions--two areas of the brain directly involved in the synthesis and release of gonadotropin-releasing hormone (GnRH). Contentious opinions concerning the influence of orexin A over the hypothalamo-gonadotropic axis have been reported in both in vivo and in vitro studies. Further studies are necessary to clarify relationships between orexin A and the hypothalamo-pituitary hormones involved in reproduction.
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