Increasing maternal plasma levels of corticotrophin-releasing hormone (CRH) during the last weeks of pregnancy suggest that this stress hormone plays an important role in the control of human parturition. Little is known about the quantitative contribution of gestational tissues (other than placenta) to intrauterine formation of CRH, urocortin and CRH-binding protein (CRH-BP), or about the distribution of CRH receptors within the uterus. We have investigated the mRNA expression of CRH, urocortin, CRH-BP and CRH receptors 1 and 2 (CRH-R1 and -R2) in gestational tissues by real-time RT-PCR. Placenta, myometrium and choriodecidua were collected after uncomplicated pregnancies at term, before the onset of labour. Distribution of CRH-R1 and CRH-R2 protein was also investigated by immunostaining with receptor subtype-specific antibodies. The placenta was identified as the main site of CRH and CRH-BP mRNA expression, displaying mRNA levels >1000 and >20 times higher than those found in the myometrium and choriodecidua respectively (P<0.05 in each case). mRNA expression of urocortin was low in all tissues investigated. Myometrium and choriodecidua expressed relevant amounts of both receptor subtypes, whereas the CRH receptor population in placenta consisted mainly of CRH-R2. The high expression of CRH in placenta and the substantial expression of CRH receptors in choriodecidua and myometrium suggested that CRH derived from placenta exerts direct or indirect actions on these tissues. Neither CRH produced by myometrium or choriodecidua nor urocortin from other intrauterine sources seem to play a major role in the control of labour.

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