O. Johren et al., Prepro-orexin and orexin receptor mRNAs are differentially expressed in peripheral tissues of male and female rats, ENDOCRINOL, 142(8), 2001, pp. 3324-3331
Orexins are produced specifically by neurons located in the lateral hypotha
lamus. Recent results suggested peripheral actions of orexins. Therefore, w
e analyzed the mRNA expression of prepro-orexin and the orexin receptor sub
types OX1 and OX2 in peripheral rat tissues. Using real-time quantitative R
T-PCR we detected significant amounts of prepro-orexin mRNA in testis, but
not in ovaries. OX1 receptor mRNA was highly expressed in the brain and at
lower levels in the pituitary gland. Only small amounts of OX1 receptor mRN
A were found in other tissues such as kidney, adrenal, thyroid, testis, ova
ries, and jejunum. Very high levels of OX2 receptor mRNA, 4-fold higher tha
n in brain, were found in adrenal glands of male rats. Low amounts of OX2 r
eceptor mRNA were present in lung and pituitary. In adrenal glands, OX2 rec
eptor mRNA was localized in the zona glomerulosa and reticularis by in situ
hybridization, indicating a role in adrenal steroid synthesis and/or relea
se. OX1 receptor mRNA in the pituitary and OX2 receptor mRNA in the adrenal
gland were much higher in male than in female rats. In the hypothalamus, O
X1 receptor mRNA was slightly elevated in female rats. The differential mRN
A expression of orexin receptor subtypes in peripheral organs indicates dis
crete peripheral effects of orexins and the existence of a peripheral orexi
n system. This is supported by the detection of orexin A in rat plasma. Mor
eover, the sexually dimorphic expression of OX1 and OX2 receptors in the hy
pothalamus, pituitary, and adrenal glands suggests gender-specific roles of
orexins in the control of endocrine functions.