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Peptides. 2006 Apr;27(4):871-7. Epub 2005 Oct 3.

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

Author information

1
Department of Analytical Medical Technology, Tohoku University School of Health Sciences, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8575, Japan. ktaka-md@mail.tains.tohuku.ac.jp

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).

PMID:
16202475
DOI:
10.1016/j.peptides.2005.08.008
[Indexed for MEDLINE]

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