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Horm Metab Res 1999; 31(11): 606-609
DOI: 10.1055/s-2007-978805
Originals Clinical

© Georg Thieme Verlag Stuttgart · New York

Effects of Orexin A on Thyrotropin-Releasing Hormone and Thyrotropin Secretion in Rats

T. Mitsuma1 , Y. Hirooka2 , Y. Mori1 , M. Kayama1 , K. Adachi1 , N. Rhue1 , J. Ping1 , T. Nogimori3
  • 1Fourth Department of Internal Medicine, Aichi Medical University, Nagakute, Aichi, Japan
  • 2Department of Laboratory Medicine, Aichi Medical University, Nagakute, Aichi, Japan
  • 3Department of Internal Medicine, Konanshowa Hospital, Konan, Aichi, Japan
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Publication History

1999

1999

Publication Date:
20 April 2007 (online)

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Effects of orexin A on secretion of thyrotropin-releasing hormone (TRH) and thyrotropin (TSH) in rats were studied. Orexin A (50 µg/kg) was injected iv, and the rats were serially decapitated. The effects of orexin A on TRH release from the rat hypothalamus in vitro and on TSH release from the anterior pituitary in vitro were also investigated. TRH and thyroid hormone were measured by individual radioimmunoassays. TSH was determined by the enzyme-immunoassay method. The hypothalamic TRH contents increased significantly after orexin A injection, whereas its plasma concentrations tended to decrease, but not significantly. The plasma TSH levels decreased significantly in a dose-related manner with a nadir at 15 min after injection. The plasma thyroid hormone levels showed no changes. TRH release from the rat hypothalamus in vitro was inhibited significantly in a dose-related manner with the addition of orexin A. TSH release from the anterior pituitary in vitro was not affected with the addition of orexin A. The findings suggest that orexin A acts on the hypothalamus to inhibit TRH release.

Key words

Orexin A - Thyrotropin-Releasing Hormone - Thyrotropin - Hypothalamus - Rat

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