Expression of orexin-A and orexin receptors in the kidney and the presence of orexin-A-like immunoreactivity in human urine

Kazuhiro Takahashi, Zenei Arihara, Takashi Suzuki, Masahiko Sone, Kumi Kikuchi, Hironobu Sasano, Osamu Murakami, Kazuhito Totsune

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17 Citations (Scopus)

Abstract

Orexin-A (hypocretin-1), a neuropeptide with stimulatory actions on arousal and appetite, was originally shown to be specifically expressed in the hypothalamus. We studied expression of orexin-A and orexin receptors in the kidney and the presence of orexin-A-like immunoreactivity in human urine. Immunocytochemistry showed that orexin-A-like immunoreactivity and two types of orexin receptors (types 1 and 2) were localized in the tubules of the human kidney obtained at autopsy. Orexin-A-like immunoreactivity was detected in human kidneys (21.3 ± 6.2 fmol/g wet weight, mean ± S.E.M., n = 4) and rat kidneys (16.2 ± 1.6 fmol/g wet weight, n = 5) by radioimmunoassay, although the levels were much lower than the levels in the brain. Orexin-A-like immunoreactivity was present in the urine obtained from male healthy volunteers (67.8 ± 4.5 pmol/l, n = 5). Reverse phase high-performance liquid chromatography showed that most of orexin-A-like immunoreactivity of the urine extract was eluted earlier than authentic orexin-A, suggesting that orexin-A-like immunoreactivity in urine was modified to hydrophilic forms. Reverse transcriptase polymerase chain reaction showed expression of orexin receptors 1 and 2 mRNAs in the human kidney. These findings suggest that orexin-A is produced by the renal tubular cells and secreted into urine. Orexin-A may act on the kidney in the autocrine or paracrine fashion, or via the urine (urocrine fashion).

Original languageEnglish
Pages (from-to)871-877
Number of pages7
JournalPeptides
Volume27
Issue number4
DOIs
Publication statusPublished - 2006 Apr

Keywords

  • Hypocretin
  • Kidney
  • Orexin
  • Urine

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Endocrinology
  • Cellular and Molecular Neuroscience

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