Role of corticotropin-releasing hormone in onset of labour

Corticotropin-releasing hormone (CRH) derived from the placenta is secreted into the maternal circulation in Targe amounts during the third trimester of human pregnancy and may have an important role in the onset of labour. A lthough the biological role of CRH remains enigmatic, the presence of funct ional CRH receptors in the myometrium suggests that CRH may modulate myomet rial contractility and hence parturition. CRH action is mediated via multip le receptor subtypes and pregnancy results in differential receptor express ion. These receptors are primarily linked to the adenylate cyclase second m essenger system, which would help the Intracellular microenvironment to mai ntain the required myometrial quiescence. CRH can exert further actions suc h as inhibition of prostaglandin production to prevent contractions. At ter m under the influence of oxytocin there is a modification in the coupling m echanisms that leads to a decrease in the biological activity of the CRH re ceptor and in the generation of cyclic adenosine monophosphate which favour s myometrial contractions. CRH, via distinct receptor subtypes, is then abl e to enhance the contractile response of the myometrium. This hypothesis pl aces CRH in a central role in coordinating the smooth transition from a sta te of relaxation to one of contraction.