Orexin A and its role in the regulation of the hypothalamo-pituitary axes in the rat.
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.
Martyńska
Lidia
L
Department of Neuroendocrinology, Medical Centre of Postgraduate Education, Marymoncka 99/103, 01-813 Warsaw, Poland. zaklad.neuroendokrynologii@cmkp.edu.pl
Polkowska
Jolanta
J
Wolińska-Witort
Ewa
E
Chmielowska
Magdalena
M
Wasilewska-Dziubińska
Elzbieta
E
Bik
Wojciech
W
Baranowska
Bogusława
B
D000818:Animals; D007987:Gonadotropin-Releasing Hormone / Q000096:biosynthesis; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D064446:Orexin Receptors; D000068797:Orexins; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D018013:Receptors, Neuropeptide / Q000378:metabolism; D012098:Reproduction / Q000502:physiology*
D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D007987:Gonadotropin-Releasing Hormone