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Human labour, both at term and preterm, is preceded by NF-κB-mediated inflammatory activation within the uterus, leading to myometrial activation, fetal membrane remodelling and cervical ripening. The stimuli triggering inflammatory activation in normal human parturition are not fully understood. We show that the neurohypophyseal peptide, oxytocin (OT), activates NF-κB and stimulates downstream inflammatory pathways in human gestational tissues. OT stimulation (1 pM-100 nM) specifically via its receptor (OTR) in human myometrial and amnion primary cells led to MAPK and NF-κB activation within 15 min and maximal p65-subunit nuclear translocation within 30 min. Both in human myometrium and amnion, OT-induced activation of the canonical NF-κB pathway upregulated key inflammatory labour-associated genes including IL-8, CCL5, IL-6 and COX-2. IKKβ inhibition (TPCA1; 10 µM) suppressed OT-induced NF-κB-p65 phosphorylation, whereas p65-siRNA knockdown reduced basal and OT-induced COX-2 levels in myometrium and amnion. In both gestational tissues, MEK1/2 (U0126; 10 µM) or p38 inhibition (SB203580; 10 µM) suppressed OT-induced COX-2 expression, but OT-induced p65-phosphorylation was only inhibited in amnion, suggesting OT activation of NF-κB in amnion is MAPK-dependent. Our data provide new insight into the OT/OTR system in human parturition and suggest that its therapeutic modulation could be a strategy for regulating both contractile and inflammatory pathways in the clinical context of term/preterm labour., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Rises in intracellular calcium are essential for contraction of human myometrial smooth muscle (HMSM) and hence parturition. The T-type calcium channel may play a role in this process. The aim was to investigate the role of the T-type calcium channel in HMSM by characterizing mRNA expression, protein localization, electrophysiological properties and function of the channel subunits Cav3.1(alpha1G), Cav3.2(alpha1H), and Cav3.3(alpha1I). QRT-PCR, immunohistochemistry, electrophysiology and invitro contractility were performed on human myometrial samples from term, preterm, labour and not in labour. QRT-PCR analysis of Cav3.1, Cav3.2 and Cav3.3 demonstrated expression of Cav3.1 and Cav3.2 with no significant change (P>0.05) associated with gestation or labour status. Immunohistochemistry localized Cav3.1 to myometrial and vascular smooth muscle cells whilst Cav3.2 localized to vascular endothelial cells and invading leucocytes. Voltage clamp studies demonstrated a T-type current in 55% of cells. Nickel block of T-type current was voltage sensitive (IC50 of 118.57+/-68.9 microM at -30 mV). Activation and inactivation curves of ICa currents in cells expressing T-type channels overlapped demonstrating steady state window currents at the resting membrane potential of myometrium at term. Current clamp analysis demonstrated that hyperpolarizing pulses to a membrane potential greater than -80 mV elicited rebound calcium spikes that were blocked reversibly by 100 microM nickel. Contractility studies demonstrated a reversible decrease in contraction frequency during application of 100 microM nickel (P<0.05). We conclude that the primary T-type subunit expressed in some MSMCs is Cav3.1. We found that application of 100 microM nickel to spontaneously contracting human myometrium reversibly slows contraction frequency.

Oxytocin and the oxytocin receptor have two important roles in labour. Evidence in all mammalian species suggests that neurohypophysical oxytocin plays a role in the expulsive phase and, although there are less supporting data, a role for oxytocin in the initiation of labour is likely. The initiation of labour may be mediated in women and rhesus monkeys by paracrine rather than endocrine mechanisms. Although initial characterisation of the oxytocin knockout mouse suggested that oxytocin is not important in this species, subsequent investigations have demonstrated that oxytocin is important for the precise timing of the onset of labour. Studies in knockout mice also confirm important interrelationships between oxytocin and prostaglandins. Oxytocin stimulates prostaglandin release in many species, mainly in the decidua/uterine epithelium. The effects of oxytocin are mediated by tissue-specific oxytocin receptor expression, which leads directly to contraction in the myometrium and prostaglandin formation in the decidua. There is a dramatic increase in oxytocin receptor expression in these tissues in late pregnancy and pharmacological inhibition delays delivery, which suggests that, in contrast to oxytocin, the oxytocin receptor is essential for normal labour.