Orexins stimulate glucocorticoid secretion from cultured rat and human adrenocortical cells, exclusively acting via the OX1 receptor

J Steroid Biochem Mol Biol. 2005 Sep;96(5):423-9. doi: 10.1016/j.jsbmb.2005.05.003.

Abstract

Orexins A and B are hypothalamic peptides, that act via two subtypes of receptors, named OX1-R and OX2-R. Rat and human adrenal cortexes are provided with both OX1-R and OX2-R, and we have previously shown that orexin-A, but not orexin-B, enhances glucocorticoid secretion from dispersed adrenocortical cells. Since OX1-Rs preferentially bind orexin-A and OX2-Rs are non-selective for both orexins, the hypothesis has been advanced that the secretagogue effect of orexin-A is exclusively mediated by the OX1-R. Here, we aimed to verify this contention and to gain insight into the signaling mechanism(s) underlying the secretagogue effect of orexins using primary cultures of rat and human adrenocortical cells. Reverse transcription-polymerase chain reaction showed that cultured cells, as freshly dispersed cells, expressed both OX1-R and OX2-R mRNAs. Orexin-A, but not orexin-B, concentration-dependently increased corticosterone and cortisol secretion from cultured rat and human adrenocortical cells, respectively. The blockade of OX1-Rs by selective antibodies abrogated the secretagogue effect of orexin-A, while the immuno-blockade of OX2-Rs was ineffective. The glucocorticoid response of cultured cells to orexin-A was annulled by the adenylate cyclase and protein kinase (PK) A inhibitors SQ-22536 and H-89, and unaffected by the phospholipase C and PKC inhibitors U-73122 and calphostin-C. Orexin-A, but not orexin-B, enhanced cyclic-AMP production from cultured cells, and did not alter inositol-3-phosphate release. Collectively, our present results allow us to conclude that orexins stimulate glucocorticoid secretion from rat and human adrenocortical cells, exclusively acting through OX1-Rs coupled to the adenylate cyclase/PKA-dependent signaling cascade.

MeSH terms

  • Adrenal Cortex / metabolism
  • Adrenal Cortex / physiology*
  • Animals
  • Cells, Cultured
  • Female
  • Glucocorticoids / metabolism
  • Humans
  • Intracellular Signaling Peptides and Proteins / physiology*
  • Male
  • Middle Aged
  • Neuropeptides / physiology*
  • Orexin Receptors
  • Orexins
  • RNA, Messenger / metabolism
  • Rats
  • Receptors, G-Protein-Coupled
  • Receptors, Neuropeptide / biosynthesis
  • Receptors, Neuropeptide / genetics
  • Receptors, Neuropeptide / physiology*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction / physiology

Substances

  • Glucocorticoids
  • HCRT protein, human
  • Intracellular Signaling Peptides and Proteins
  • Neuropeptides
  • Orexin Receptors
  • Orexins
  • RNA, Messenger
  • Receptors, G-Protein-Coupled
  • Receptors, Neuropeptide