Changes in uterine innervation in pregnancy and during labour:

Novel identification and modulation of the mechanosensitive Piezo1 channel in human myometrium

Approximately 10% of US births deliver preterm before 37 weeks of completed gestation. Premature infants are at risk for life-long debilitating morbidities and death, and spontaneous preterm labour explains 50% of preterm births. In all cases existing treatments are ineffective, and none are FDA approved. The mechanisms that initiate preterm labour are not well understood but may result from dysfunctional regulation of quiescence mechanisms. Human pregnancy is accompanied by large increases in blood flow, and the uterus must enlarge by orders of magnitude to accommodate the growing fetus. This mechanical strain suggests that stretch-activated channels may constitute a mechanism to explain gestational quiescence. Here we identify for the first time that Piezo1, a mechanosensitive cation channel, is present in the uterine smooth muscle and microvascular endothelium of pregnant myometrium. Piezo is downregulated during preterm labour, and stimulation of myometrial Piezo1 in an organ bath with the agonist Yoda1 relaxes the tissue in a dose-dependent fashion. Further, stimulation of Piezo1 while inhibiting protein kinase A, AKT, or endothelial nitric oxide synthase mutes the negative inotropic effects of Piezo1 activation, intimating that actions on the myocyte and endothelial nitric oxide signalling contribute to Piezo1-mediated contractile dynamics. Taken together, these data highlight the importance of stretch-activated channels in pregnancy maintenance and parturition, and identify Piezo1 as a tocolytic target of interest. KEY POINTS: Spontaneous preterm labour is a serious obstetric dilemma without a known cause or effective treatments. Piezo1 is a stretch-activated channel important to muscle contractile dynamics. Piezo1 is present in the myometrium and is dysregulated in women who experience preterm labour. Activation of Piezo1 by the agonist Yoda1 relaxes the myometrium in a dose-dependent fashion, indicating that Piezo1 modulation may have therapeutic benefits to treat preterm labour.

Sensory neuron LKB1 mediates ovarian and reproductive function

Treatments for reproductive disorders in women primarily consist of hormone replacement therapy, which can have negative health impacts. Bidirectional communication between sensory neurons and innervated organs is an emerging area of interest in tissue physiology with potential relevance for reproductive disorders. Indeed, the metabolic activity of sensory neurons can have profound effects on reproductive phenotypes. To investigate this phenomenon, we utilized a murine model with conditional deletion in sensory neurons of liver kinase B1 (LKB1), a serine/threonine kinase that regulates cellular metabolism. Female mice with this LKB1 deletion (Nav1.8cre;LKB1fl/fl) had significantly more pups per litter compared to wild-type females. Interestingly, the LKB1 genotype of male breeders had no effect on fertility outcomes, thus indicating a female-specific role of sensory neuron metabolism in fertility. LKB1 deletion in sensory neurons resulted in reduced ovarian innervation from dorsal root ganglia neurons and increased follicular turnover compared to littermate controls. In summary, LKB1 expression in peripheral sensory neurons plays an important role in modulating fertility of female mice via ovarian sensory innervation.

Identification of a novel distension-evoked motility pattern in the mouse uterus

The dynamic changes in uterine contractility in response to distension are incompletely understood. Rhythmic, propagating contractions of nonpregnant uterine smooth muscle occur in the absence of nerve activity (i.e., myogenic), events that decline during pregnancy and reemerge at parturition. We therefore sought to determine how myogenic contractions of the nonpregnant uterus are affected by distension, which might provide mechanistic clues underlying distension-associated uterine conditions such as preterm birth. Uteri isolated from nulliparous adult female mice in proestrus were video imaged to generate spatiotemporal maps, and myoelectrical activity simultaneously recorded using extracellular suction electrodes. Motility patterns were examined under basal conditions and following ramped intraluminal distension with fluid to 5 and 10 cmH₂O. Intraluminal distension caused pressure-dependent changes in the frequency, amplitude, propagation speed, and directionality of uterine contractions, which reversed upon pressure release. Altered burst durations of underlying smooth muscle myoelectric events were concurrently observed, although action potential spike intervals were unchanged. Voltage-gated sodium channel blockade [tetrodotoxin (TTX); 0.6 µM] attenuated both the amplitude of contractions and burst duration of action potentials, whereas all activity was abolished by L-type calcium channel blockade (nifedipine; 1 µM). These data suggest that myogenic motility patterns of the nonpregnant mouse uterus are sensitive to changes in intraluminal pressure and, at high pressures, may be modulated by voltage-gated sodium channel activity. Future studies may investigate whether similar distension-evoked changes occur in the pregnant uterus and the possible pathophysiological role of such activity in the development of preterm birth.

A novel visceral pain model of uterine cervix inflammation in rat

Treatment of visceral pain originating from the uterine cervix is a substantial clinical problem. The underlying mechanisms of such visceral pain remain unclear mainly due to a lack of reliable model. This study aimed to develop and evaluate the performance of a rat model of pain induced by uterine cervix inflammation. Rats were randomized to six groups according to the solution injected into the uterine cervix: normal saline, vehicle, capsaicin (0.3 mg, 0.6 mg, 0.9 mg), capsaicin 0.9 mg + morphine (n = 15 in each group). Spontaneous behaviors after cervical injection were recorded by a computerized video system and analyzed offline. An equation for calculating a novel pain score was derived from particular behaviors, based on Pearson's correlation analysis and regression analysis. c-Fos expression in the spinal cord was detected. The pain score and c-fos expression in the spinal cord were highest in the 0.9 mg capsaicin group and lowest in the normal saline and vehicle groups (P < 0.05). Intrathecal morphine significantly decreased the pain score (P < 0.05) and c-fos expression in the spinal cord (P < 0.05). Injection of capsaicin into the uterine cervix in rats could be a practical model of inflammatory cervical pain, which can be evaluated using our novel pain score. This model will provide further insight into the mechanism underlying visceral pain originating from the uterine cervix.

Non-Invasive Ring Electrode With a Wireless Electrical Recording and Stimulating System for Monitoring Preterm Labor

Preterm labor and birth are the primary causes of neonatal morbidities and mortalities. The early detection and treatment of preterm uterine muscular contraction are crucial for the management of preterm labor. In this work, a ring electrode with a wireless electrical recording and stimulating (RE-WERS) system was designed, fabricated, and investigated for the non-invasive monitoring of uterine contraction/relaxation as a diagnostic and therapeutic tool for preterm labor. By using an organ bath system, we confirmed that the uterine contraction force in mice can be decreased by the application of electrical stimulation. Then, the RE-WERS system was inserted non-invasively through the vagina to the cervix of a pregnant minipig, and it successfully recorded the uterine contraction and reflect signals when various electrical stimulating conditions were applied. The difference in the uterine signals before and after the injection of a labor induction drug, such as oxytocin and prostaglandin [Formula: see text], was recorded, and the difference was remarkable. In addition, the uterine signal that was recorded was well matched with the signal of the electromyography (EMG) kit during open abdominal surgery. It seemed that the continuous and various electrical stimulations affected the delay or inhibition of childbirth in the pregnant minipig.

Vulvodynia

Vulvodynia is a condition that occurs in 8-10% of women of all ages and is characterized by pain at the vulva that is present during sexual and/or non-sexual situations. Diagnosis is established through careful medical history and pelvic examination, including the cotton-swab test. The onset and maintenance of vulvodynia involves a complex interplay of peripheral and central pain mechanisms, pelvic floor muscle and autonomic dysfunction, anxiety, depression and childhood maltreatment as well as cognitive-affective, behavioural and interpersonal factors. Given the absence of empirically supported treatment guidelines, a stepwise approach of pelvic floor physical therapy and cognitive behavioural therapy as well as medical management is suggested, with surgery as the last option. Vulvodynia has a negative effect on the quality of life of women and their partners, and imposes a profound personal and societal economic burden. In addition, women with vulvodynia are more likely to report other chronic pain conditions, which further alters their quality of life. Future efforts should aim to increase girls', women's and healthcare professionals' education and awareness of vulvodynia, phenotype different subgroups of women based on biopsychosocial characteristics among more diverse samples, conduct longitudinal studies and improve clinical trial designs.

Effect of chronic pretreatment with 17β-estradiol and/or progesterone on the nociceptive response to uterine cervical distension in a rat model

It is widely known that visceral pain is more prevalent in women than in men, and this phenomenon is interpreted as a consequence of the gonadal hormone modulation of pain perception and transduction. Uterine cervical distension might cause obstetric and gynecologic pain with clinical relevance to visceral pain. In this study, we focused on the roles of 17β-estradiol and progesterone in visceral nociception with the use of a rat model of uterine cervical distension. Female ovariectomized rats were injected with 17β-estradiol (E₂) or progesterone (P₄) for 21 days, after which visceral pain-induced spinal c-fos expression and visceromotor reflex changes were compared between ovariectomized and hormone-substituted groups. We found that uterine cervical distension induced a drastic increase in spinal c-fos expression and visceromotor reflex activity, and ovariectomy inhibited the increase in c-fos expression induced by visceral pain; this inhibition was reversed by estrogen but not progesterone replacement. This study demonstrates that estrogen is involved in uterine cervical nociception, while progesterone plays less of a significant role.

"Luteal Analgesia": Progesterone Dissociates Pain Intensity and Unpleasantness by Influencing Emotion Regulation Networks

Background: Pregnancy-induced analgesia is known to occur in association with the very high levels of estradiol and progesterone circulating during pregnancy. In women with natural ovulatory menstrual cycles, more modest rises in these hormones occur on a monthly basis. We therefore hypothesized that the high estradiol high progesterone state indicative of ovulation would be associated with a reduction in the pain experience. Methods: We used fMRI and a noxious thermal stimulus to explore the relationship between sex steroid hormones and the pain experience. Specifically, we assessed the relationship with stimulus-related activity in key regions of networks involved in emotion regulation, and functional connectivity between these regions. Results: We demonstrate that physiologically high progesterone levels are associated with a reduction in the affective component of the pain experience and a dissociation between pain intensity and unpleasantness. This dissociation is related to decreased functional connectivity between the inferior frontal gyrus and amygdala. Moreover, we have shown that in the pre-ovulatory state, the traditionally "male" sex hormone, testosterone, is the strongest hormonal regulator of pain-related activity and connectivity within the emotional regulation network. However, following ovulation the traditionally "female" sex hormones, estradiol and progesterone, appear to dominate. Conclusions: We propose that a phenomenon of "luteal analgesia" exists with potential reproductive advantages.

Pain Relief Effect of Cryotherapy in Parturients

INTRODUCTION: Pain in childbirth and strategies for relieving it have been a subject of interest to researchers for many years. The use of cold (cryotherapy), as a pain relief technique generally, is quite well known and studied. However, few studies have addressed the use of cryotherapy as a strategy for relieving the pain of childbirth.

OBJECTIVE: To evaluate the effects of cryotherapy in relieving childbirth pain.

METHOD: Pilot intervention study using prospective data in a single intervention group, the outcome being the pain relief in women in labor. The sample comprised 36 parturients at the Hospital Maternidade Carmela Dutra, Rio de Janeiro, Brazil. Cryotherapy was applied to the parturients’ thoracolumbar region at cervical dilation of 5, 7, and/or 9 cm, using an icepack belt. In all, 48 applications were made. The responses regarding the action of cryotherapy on pain were recorded on a specific form. The Numeric Rating Scale (NRS) was used. Following a form, the parturients’ behavior during the application of cryotherapy was also observed.

RESULTS: It was found that 91.67% (outcome) of the women reported pain relief and better conditions in which to experience childbirth. The behavior of 75% of the women in labor was calm and participatory; some slept (5.56%), others took short naps (19.44%).

CONCLUSION: Cryotherapy proved effective in relieving pain in childbirth. Because characteristically, cryotherapy does not interfere in the physiological process of childbirth, it can be used in care for women in labor.

Paracervical block as pain treatment during second-trimester medical termination of pregnancy: an RCT with bupivacaine versus sodium chloride

STUDY QUESTION

Can paracervical block (PCB) administered before the onset of pain decrease women's pain experience during second-trimester medical termination of pregnancy (MToP)?

SUMMARY ANSWER

There were no clinically significant differences between groups receiving PCB with bupivacaine or saline with regard to the highest and lowest pain intensity, morphine consumption or induction-to abortion interval.

WHAT IS KNOWN ALREADY

The most common side effect of misoprostol is pain; nevertheless, there are sparse studies in pain and pain treatment during MToP, especially in second-trimester abortion. Pain reported in second-trimester medical abortion is often intense, and peaks when the fetal expulsion occurs.

STUDY DESIGN, SIZE, DURATION

A double-blinded RCT was carried out from May 2012 until April 2015. A power calculation was based on a previous pilot study showing that the proportion of women with severe pain [visual analogue scale (VAS) ≥7] was 63%. A clinically significant reduction was considered to yield 35% with severe pain, and with a power of 80% and significance level of 5% (two-sided) 112 women were needed. Accounting for a 20% drop-out rate, a total of 140 women were needed. The primary outcome, pain intensity measured as any VAS ≥7, was analysed using a generalized estimating equations model. The level of significance was set to P < 0.05 two-sided. A computer generated randomization list with block size of 10 was used. The treatment allocation was placed in a sealed, opaque, envelope and picked consecutively.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 589 women attending a gynaecological clinic had a second-trimester abortion during the study period and 276 were invited to participate. A total of 113 women undergoing abortion from 13 weeks of gestation and above were recruited, of which 55 were randomly allocated to receive a PCB with bupivacaine and 58 a PCB with sodium chloride 1 h after the first dose of misoprostol. The full analysis set (FAS) population was defined as all randomized women that had at least one value for any of the outcomes (n = 102). The per-protocol (PP) population was defined as a subset of the FAS excluding patients with major protocol deviations or without a value for the primary outcome (n = 99). Pain was measured by VAS at misoprostol initiation (baseline) and repeated every 30 min until fetal expulsion. The primary outcome was the highest VAS pain intensity at any time point.

MAIN RESULTS AND THE ROLE OF CHANCE

The highest pain intensity, did not show any differences at a cut-off of VAS ≥7 [risk ratio (RR): 1.1; 95% confidence interval (CI): 0.9-1.5; P = 0.0.292]. In the PP analyses, there were 75% women in the bupivacaine group and 64% in the sodium chloride group with VAS ≥7 (RR: 1.2; 95% CI: 0.9-1.5; P = 0.235). Most women did not experience pain at the misoprostol start, 19 women scored a VAS of >0, ranging from 1 to 4 with a mean of 1.8 and median of 2 (P = 1.000). Immediately prior to PCB, 61 women scored a VAS of >0, from 1 to 10 with a mean of 2.0 and median of 1 (P = 0.771). There was a 48% loss of VAS scores at the time of expulsion and the remaining scores did not differ between groups (RR: 1.5; 95% CI: 0.9-2.5). A subgroup analysis of primipara did not show any difference in highest pain intensity VAS ≥7 (RR: 1.2; 95% CI: 0.9-1.6; P = 0.283). No statistically significant differences were observed between groups with regard to the highest and lowest (P = 553 and 0.182) pain intensity and morphine consumption (P = 0.772). Side effects were reported by 28 women (14 women in each group), with no differences between groups. Most common was nausea and vomiting in connection to morphine injection.

LIMITATIONS, REASONS FOR CAUTION

Nearly 60% of the invited women did not want to participate in the study (fear of needles and fear of receiving the placebo) therefore women who tolerate pain may have been overrepresented in the study population. Data collection was stopped, in error, when 113 participants had been recruited. The loss to follow-up was, however, only 11 women (10%), which was lower than expected but intrinsically the study did not fully reach the intended number of women, which may have influenced the results. In addition, the obstetrical and gynaecological background of participating women differs. The participants were informed that they had a 50% chance of receiving a PCB with active substance, which could theoretically have affected their expectations and pain experience (placebo effect). The frequent attention at VAS scoring and the overall care provided may also have affected the participants in a positive way, and helped women to feel supported and more relaxed during the abortion.

WIDER IMPLICATIONS OF THE FINDINGS

The highest pain intensity was severe (VAS: 7-10) among 65-75% of the participants, as reported for first-trimester medical abortion; however, the maximal pain scores remain high despite the PCB. There is, therefore, a clear need for more optimal pain treatment but only limited data exist on pain treatment during MToP over all gestational lengths. As PCB was well tolerated, did not cause any serious side effects and had no negative impact on the abortion process and efficacy, another approach may be worth exploring, namely PCB given on demand at the onset of painful contractions.

STUDY FUNDING/COMPETING INTERESTS

The study was supported by grants from the Swedish Research Council (grant no: 2012-2844), ALF (Karolinska Institutet - Stockholm County Council, Agreement on Medical Research and Training) funding, the Karolinska Institutet, Stockholm South General Hospital, and Swedish Nurses in the Area of Pain - SSOS together with GlaxoSmithKline. None of the authors have any conflicts of interest.

TRIAL REGISTRATION NUMBER

The trial was registered with ClinicalTrials.gov (identifier: NCT01617564) and The EudraCT (number: 2010-020780-21) and was approved by The Regional Ethical Review Board at Karolinska Institutet (dnr: 2007/1277-31/2 and 2010/410-31/1).

TRIAL REGISTRATION DATE

Clinical trial registration was done in May 2012 before initiation of patient recruitment.

DATE OF FIRST PATIENT'S ENROLMENT

29 May 2012.

Increased nerve fibers in placental bed myometrium in women with preeclampsia

Narrowing of the uterine spiral arterioles below the deciduomyometrial junction is 1 of the key pathophysiological changes in women with preeclampsia. The contribution of pelvic autonomic nerves to decidualization and impaired placentation in preeclampsia is not clear. Placental bed biopsies were obtained from 10 women with preeclampsia and 23 nornotensive women at caesarean section. We stained them with anti-S100 and CD34 antibodies to detect the presence of nerve fibers and blood vessels, respectively. We detected S100-immunoactive nerve fibers in the myometrium but not in the decidua in both groups of women. S100-immunoactive nerve fiber density in the placental bed myometrium was significantly increased in women with preeclampsia compared to normotensive women. There was no clear relationship between the densities of nerve fibers and CD34-positive blood vessels in these biopsies. These results suggest increased nerve fibers in the placental bed myometrium may play a role in the pathogenesis of the preeclampsia.