Enhanced myometrial autophagy in postpartum uterine involution

ObjectiveTo understand the mechanisms of postpartum uterine involution, we investigated the uterine myometrial changes during pregnancy and the postpartum period.Materials and methodsNine groups of uterine myometrial samples from mice (n = 4) were collected on gestational Day 0 (nonpregnant), Day 1, Day 2, Day 7, Day 14, and Day 21 and on postpartum Day 1, Day 2, and Day 7. Human samples of uterine myometrium on term (n = 1) and postpartum Day 1 (n = 2) were also collected. Ki-67 immunostaining was used to determine myometrial proliferation. For cell hypertrophy analysis, organelle proteins, β-actin, prohibin, calnexin, and golgin-97 were analyzed by Western blotting. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and evaluation of activated caspase-3 expression by Western blot analysis assay were used to detect apoptosis. Autophagy was assayed via the evaluation of LC3 expression by Western blotting, immunohistochemistry, and autophagosomes by electron microscopy.ResultsUterine myocytes proliferated during the early stage of gestation with a peak at Day 2, whereas myocyte hypertrophy with increased cellular organelle production occurred gradually in later stages of pregnancy. Postpartum autophagy developed abruptly in uterine myocytes without obvious apoptosis.ConclusionAutophagy of myocytes may play an important role in uterine involution. These results have implications for our understanding of myometrial functional adaptations during pregnancy and the physiological role of autophagy in the uterine remodeling events in the postpartum period.     

肿瘤转移抑制因子CD9/MRP-1基因在小鼠围着床期子宫内膜的动态表达

目的:探讨肿瘤转移抑制基因(CD9)/运动相关蛋白(MRP-1)mRNA和蛋白在胚胎着床过程中的作用。方法:应用RT-PCR和免疫组化技术观察CD9/MRP-1mRNA和蛋白在早孕和假孕小鼠子宫中的表达规律。结果:早孕d1-4小鼠子宫组织均有CD9/MRP-1mRNA表达,且d4表达最多;其蛋白主要表达在d1-4的子宫内膜上皮细胞,且早孕d2-4CD9/MRP-1在子宫基质细胞散在阳性表达。假孕d1-8小鼠子宫组织均有CD9/MRP-1mRNA表达,假孕d5表达开始增加,至d6达到峰值。而CD9/MRP-1蛋白在假孕d1-8子宫内膜腺上皮均有表达,而子宫内膜腔上皮均无表达。假孕d2-5,子宫基质细胞出现散在阳性表达。结论:①CD9/MRP-1在早孕小鼠子宫中呈动态表达,提示它在胚胎精确侵袭子宫内膜的调节中发挥作用。②CD9/MRP-1在妊娠小鼠子宫的表达是非胚胎依赖性的。     

Barbed sutures versus conventional sutures for uterine closure at cesarean section; a randomized controlled trial

Introduction: The aim of this randomized control trial was to compare the operative data and the early postoperative outcomes of cesarean sections in which the uterine incision was closed with a barbed suture (STRATAFIX? Spiral PDO Knotless Tissue Control Device, SXPD2B405, Ethicon Inc.) with those of cesarean sections in which the uterine incision was closed with a conventional smooth suture (VICRYL^?; Ethicon Inc.).

Materials and methods: One hundred pregnant patients were randomized in a 1:1 ratio to the Stratafix group or the Vicryl group. The uterine incision was closed by two layers of sutures in both groups. In the Vicryl group, the first layer was continuous and the second layer was interrupted. In the Stratafix group, both layers were continuous.

Results: The uterine closure time was significantly lower in the Stratafix group (224?±?46 versus 343?±?75?s, p?p value?=?.009). The mean blood loss during closure of uterine incision and mean hospital stay were lower in the Stratafix group but these differences failed to reach statistical significance.

Conclusion: The use of barbed suture for uterine incision closure at cesarean section is associated with shorter uterine closure time and similar early perioperative complications compared with conventional smooth suture. The difference between both groups in the technique of suturing the second layer of the uterine incision may be the cause of the reduction in the uterine closure time and the need for additional sutures to achieve hemostasis during suturing the uterine incision with a barbed suture. Further, well designed randomized controlled trials should be conducted to investigate the association between the type of suture (barbed or conventional smooth) and remote complications of cesarean section (infertility, pelvic pain, abnormal placentation and rupture uterus).     

Clinical experiences of ICSI-ET thawing cycles with embryos cryopreserved at different developmental stages

Purpose: The aim of our study was to analyze factors including survival, implantation and pregnancy rate, patients’ age and BMI, abortions and extra uterine pregnancies that might influence the outcome of ICSI-ET thawing cycles.Methods: A total of 147 cycles with embryos cryopreserved at different developmental stages were retrospectively evaluated.Results: No difference was found in the survival, implantation and pregnancy rates of embryos cryopreserved on Day 2–3 and 5. However, in the pregnant group significantly higher implantation rate was observed with Day 5 blastocysts then with Day 2 or 3 early embryos. We found no difference in the number of abortions and extra uterine pregnancies between fresh and frozen ICSI-ET cycles. Higher BMI was found in the pregnant than in the non-pregnant group. However, the age of patient had no effect on the results.Conclusions: Developmental stage of embryo and patients’ BMI influences the success of ICSI-ET thawing cycles.     

Aging blunts remodeling of the uterine artery during murine pregnancy

OBJECTIVE: The progressive increase in uterine blood flow (UBF) during pregnancy is accommodated by morphologic changes in the uterine artery (UA) in a process defined as arterial remodeling. This process is accompanied by changes in cytoskeletal architecture of the arterial smooth muscle cells (SMCs) and surrounding extracellular matrix (ECM). Aging reduces flow-induced arterial remodeling. We studied changes in the murine UA during pregnancy and on the effects of aging on the capacity of the UA to remodel in response to pregnancy. METHODS: We determined morphologic and cytologic changes in UA from nonpregnant and pregnant mice aged 12 weeks (young) and 40 weeks (old) and correlated them with their reproductive performance. RESULTS: In young mice, pregnancy induced an early increase in UA wall mass, which preceded lumen widening. These changes were not accompanied by altered densities of elastin and collagen in the ECM of the medial layer. Smooth muscle cell proliferation increased in midpregnancy and was paralleled by a transient decrease in smoothelin and smooth muscle alpha-actin expression. In old mice, these pregnancy-dependent changes in the UA wall were either absent or markedly reduced. Although by day 11 of pregnancy litter size did not differ between both age groups, the number of viable pups in old mice by day 17 of pregnancy and at birth was 25% and 60% less than in young mice. CONCLUSION: Outward hypertrophic remodeling of the UA during pregnancy in young mice is characterized by transient phenotypic modulation and proliferation of SMCs and alterations in the composition of the ECM. In contrast, in older mice, UA remodeling is markedly reduced and accompanied with a loss of viable fetuses near term pregnancy.     

Distribution of some Gal beta 1-3(4)GlcNAc related carbohydrate antigens on the mouse uterine epithelium in relation to the peri-implantational period

Using monoclonal antibodies of defined carbohydrate specificity we have looked at the distribution of various Gal beta 1-3(4)GlcNAc related oligosaccharide determinants in the mouse uterus during the first 6 days of pregnancy. Frozen sections of uterus from B6D2F1, B6CBF1 or B6D2F1/BOM female mice were incubated with the monoclonal antibodies and then with a fluorescein isothiocyanate conjugate of goat anti-mouse IgM and viewed by epifluorescence illumination. None of the antibodies bound specifically to stroma cells but antibodies recognising difucosylated Gal beta 1-3(4)GlcNAc structures, the monofucosylated type II determinant (SSEA-1) and an H type I oligosaccharide bound to cells of the uterine luminal epithelium and glands and to the uterine secretions. Antibodies recognising the three different types of saccharide showed independent changes in staining intensity during early pregnancy. The antibody which recognises H type I structures (667/9E9) showed a change in distribution from binding to most cells of the uterine epithelium in the non-pregnant mouse and on day 3 of pregnancy to binding restricted to areas of epithelial cells interspersed with non-staining clumps of cells between days 4 and 5 of pregnancy.     

Pregnancy and Placenta Increta in a Noncommunicating Uterine Horn

BackgroundWe present a rare case of pregnancy and invasive placentation in a unruptured, noncommunicating rudimentary uterine horn at 20 weeks’ gestation.CaseThe patient was followed with ultrasound throughout early pregnancy and initial imaging for dating purposes showed a pregnancy within a communicating right horn of the uterus. At the 18-week anatomy ultrasound, the pregnancy was discovered to be within the noncommunicating, rudimentary left horn of the uterus. This was confirmed using pelvic magnetic resonance imaging. The patient opted for surgical management and subsequently underwent laparotomy and removal of the noncommunicating uterine horn and pregnancy. Placental tissue was adherent to the level of the serosa during surgery and pathologic diagnosis was significant for a placenta increta.Summary and ConclusionThe patient recovered well from surgery and subsequently went on to have a successful term pregnancy delivered via cesarean section for breech in the right horn 15 months later.     

Negative uterine asynchrony retards early equine conceptus development and upregulation of placental imprinted genes

IntroductionPlacental imprinted genes appear to be sensitive indicators of an inappropriate pre-implantation environment. This study examined the effects of negative uterine asynchrony after embryo transfer (ET) on early horse embryo development, and yolk-sac membrane expression of DNA methyltransferases (DNMTs) and equine specific placental imprinted genes.MethodsDay 8 embryos were transferred to recipient mares on day 8 (synchronous) or day 3 (asynchronous) after ovulation, and conceptuses were recovered 6 or 11 days later (day 14 or 19 of development).ResultsDay 14 conceptuses recovered from an asynchronous uterus had a smaller embryonic disc, in which primitive streak development was visibly retarded compared to conceptuses from a synchronous uterus. Similarly, length, somite number and organogenesis were retarded in day 19 embryos after asynchronous ET. Maternal (GRB10, H19, IGF2R, PHLDA2) and paternal (IGF2, INSR, PEG3, PEG10, DIO3, NDN, SNRPN) imprinted genes and DNMTs (DNMT1, 3A and 3B) were all up-regulated between day 14 and 19 of pregnancy and, for most, mRNA expression was higher in synchronous than asynchronous day 19 yolk-sac membrane. Expression of the paternally imprinted gene HAT1 increased between day 14 and 19 of pregnancy, but was not affected by the asynchrony.DiscussionConceptus development and upregulation of DNMTs and imprinted genes were delayed rather than dysregulated after transfer into a negatively asynchronous uterus. We propose that this ability to ‘reset’ conceptus development to uterine stage is an adaptation that explains why horse embryos are unusually tolerant of asynchrony after ET.     

Caprine uterine and placental osteopontin expression is distinct among epitheliochorial implanting species

Osteopontin (OPN) is the most highly up-regulated extracellular matrix/adhesion molecule in the uterus of humans and domestic animals as it becomes receptive to implantation. Studies in sheep and pigs have shown that OPN is a component of ovine and porcine histotroph characterized by a complex temporal and spatial pattern of uterine and conceptus expression involving immune, epithelial, and stromal cells. It is proposed that these expression events are orchestrated to contribute to conceptus attachment and placentation. However, differences in OPN expression between sheep and pigs have been detected that relate to differences in placentation. Therefore, this study examined OPN expression in the caprine uterus and conceptus to gain insight into mechanisms underlying OPN function(s) during pregnancy through comparative analysis of differences in placentation between pigs, sheep, and goats. Goats were hysterectomized (n = 5/day) on Days 5, 11, 13, 15, 17 or 19 of the estrous cycle, and Days 5, 11, 13, 15, 17, 19 or 25 of pregnancy. Slot-blot hybridization showed increases in endometrial OPN mRNA beginning on Day 17 of the estrous cycle and Day 19 of pregnancy. In situ hybridization localized OPN mRNA to endometrial glandular epithelium (GE), Day 25 myometrium, and cells scattered within the placenta hypothesized to be immune. Immunofluorescence microscopy detected OPN protein on the apical surface of endometrial lumenal epithelium (LE), in GE, and on conceptus (Tr). Western blot analysis detected primarily the native 70-kDa OPN protein in endometrial extracts from the estrous cycle and pregnancy, as well as in uterine flushings from pregnant goats. Co-induction of OPN and alpha-smooth muscle actin, but not desmin proteins, was observed in uterine stroma by Day 25 of pregnancy. OPN in cyclic GE, Day 25 myometrium, and desmin-negative endometrial stroma is unique and reflects subtle differences among superficial implanting species that correlate with the depth of Tr invasion.     

High expression of cyclooxygenase-2 in uterine fibroids and its correlation with cell proliferation

Objective

To investigate the expression of cyclooxygenase-2 (COX-2) in uterine fibroids and healthy uterine smooth muscle as well as its role in the pathogenesis of uterine fibroids.

Methods

We collected uterine fibroid tissues and their paired adjacent healthy uterine smooth muscle tissues from 30 cases of uterine fibroids. We used immunohistochemistry and quantitative real-time PCR, as well as western blot to detect COX-2 expression. Using the COX-2 inhibitors NS-398 and celecoxib, we observed the response to the inhibitors in the healthy and fibroid smooth muscle cell pairs.

Results

COX-2 was detected by immunohistochemistry in both uterine fibroids and uterine smooth muscle, with higher immunoreactivity in uterine fibroids; the positive index of the smooth muscle cells was 11.90 and the positive index of uterine fibroids cells was 46.50 (P < 0.05). The expression of COX-2 mRNA in uterine fibroids was higher (0.122 ± 0.062) than in normal smooth muscle tissue (0.025 ± 0.009; P < 0.05). Also, the western blot results showed that COX-2 expression was significantly higher in uterine fibroid cases, as compared to the expression in uterine smooth muscle. Immunofluorescence showed that the occurrence of COX-2 was obviously higher in smooth muscle cells of uterine fibroids than in the healthy smooth muscle cells. NS-398 or celecoxib significantly inhibited the proliferation of smooth muscle cells of uterine fibroids, but did not inhibit the proliferation of healthy smooth muscle cells. Accordingly, NS-398 or celecoxib significantly reduced the expression of the downstream metabolite of COX-2, PGE2, in the smooth muscle cells of uterine fibroids, but not in healthy smooth muscle cells.

Conclusion

COX-2 expression in uterine fibroids was significantly higher than in healthy uterine smooth muscles. The inhibition of COX-2 activity significantly reduced the proliferation of smooth muscle cells of the uterine fibroids, suggesting that COX-2 plays an important role in the pathogenesis of uterine fibroids.     

Uterine prolapse in pregnancy: risk factors,complications and management

Abstract

Presentation of uterine prolapse is a rare event in a pregnant woman, which can be pre-existent or else manifest in the course of pregnancy. Complications resulting from prolapse of the uterus in pregnancy vary from minor cervical infection to spontaneous abortion, and include preterm labor and maternal and fetal mortality as well as acute urinary retention and urinary tract infection. Moreover, affected women may be at particular risk of dystocia during labor that could necessitate emergency intervention for delivery. Recommendations regarding the management of this infrequent but potentially harmful condition are scarce and outdated. This review will examine the causative factors of uterine prolapse and the antepartum, intrapartum and puerperal complications that may arise from this condition as well as therapeutic options available to the obstetrician. While early recognition and appropriate prenatal management of uterine prolapse during pregnancy is imperative, implementation of conservative treatment modalities throughout pregnancy, these applied in accordance with the severity of the uterus prolapse and the patient’s preference, may be sufficient to achieve uneventful pregnancy and normal, spontaneous delivery.     

微波子宫内膜去除术中组织热损伤的观察

目的探讨微波子宫内膜去除术（MEA）中热效应对组织结构的影响,寻求适宜的内膜薄化方法和微波作用方式。方法对离体和在体子宫分别行全面刮宫薄化内膜后的MEA（刮宫组）和早卵泡期（未刮宫）直接MEA（早卵泡期组）。术中将微波探头移动方式设为“z”形和“z＋w”形两种方式,同时测量宫底、两侧宫角、子宫后壁及前壁下段的子宫浆膜面温度。并将作用后的子宫标本切片行HE染色、尼克酰胺腺嘌呤核苷酸-黄递酶（NADH-d）染色,光学显微镜（光镜）、电子显微镜（电镜）下观察组织热损伤后的形态学改变及损伤深度。结果（1）光镜下见子宫内膜腺体扭曲、细胞界限消失,核浓染,间质中大量急性炎性细胞浸润;浅肌层细胞核固缩、浓染,胞质浓缩,细胞排列密集;深层肌细胞无改变。NADH-d染色可见损伤后的子宫内膜层及部分浅肌层为无色区;宫壁组织热损伤的范围清晰可辨。电镜下坏死部分的平滑肌细胞核染色质、核膜、细胞膜被破坏;线粒体肿胀、膜破裂、嵴消失,细胞器被大量破坏;坏死与正常平滑肌移行区的平滑肌细胞核染色质轻度破坏;核膜及细胞膜存在,线粒体高度水肿,粗面内质网轻度扩张、脱颗粒。（2）离体子宫与在体子宫的最高温度均位于子宫后壁,分别为50．9oC和37．6oC,两者比较,差异有统计学意义（P〈0．01）。（3）离体子宫的宫体组织热损伤深度为4．0～8．8mill,颈体交界处为1．6～3．8mill。在体子宫的宫体组织热损伤深度为4．1～6．6mm,颈体交界处为0—2．8mm。子宫后壁的损伤深度最深,与宫底、两侧宫角及前壁下段等部位比较,差异均有统计学意义（P〈0．01）。离体子宫及在体子宫的对应部位之间损伤深度比较,差异均有统计学意义（P〈0．05）。刮宫组和早卵泡期组的组织热损伤深度比较,差异无统计学意义（P〉0．05）;微波探头以“z＋w”形移动时,组织损伤深度明显深于“z”形移动方式,两者比较,差异有统计学意义（P〈0．05）。结论全面刮宫后和早卵泡期施行MEA均可有效去除子宫内膜,其热损伤深度可控。     

Unexpected uterine smooth muscle tumor of uncertain malignant potential and sarcoma: A single center cohort study in South Korea

ObjectiveTo evaluate the risk of encountering unexpected uterine smooth muscle tumors of uncertain malignant potential (STUMPs) or sarcomas during surgical treatment of mesenchymal tumors of the uterus using morcellation.Material and methodsData were collected retrospectively from subjects who were pathologically diagnosed with uterine leiomyoma or its variants, STUMP or other premalignant mesenchymal tumors of uterus, or sarcoma during surgical treatment between July 2014 and June 2017.ResultsA total of 3785 women were investigated; 2824 laparoscopic procedures (74.6%) were performed, and an electronic power morcellator was used in 1636 patients (43.2%). Sixteen women (0.42%) were diagnosed with STUMP and 14 (0.37%) were diagnosed with uterine sarcoma. The incidence rate of unexpected STUMP or uterine sarcoma was 0.61% (23 of 3785 women); unexpected STUMP in 13 (0.34%), and unexpected sarcoma was in 10 (0.26%). Moreover, the unexpected leiomyosarcoma rate was 0.08% (3 in 3785). The rate of unintended morcellation of STUMPs was relatively high at 0.26% (10 in 3785), however, that for uterine sarcomas was 0.05% (2 in 3785).ConclusionThe risks of unintended morcellation were very low for sarcomas and STUMPs, although the risk of the latter was approximately 5-fold that of the former. To reduce the unintended dissemination of tumors, patients suspected of having malignancies should be provided adequate information regarding their treatment options as well as their associated risks. Meanwhile, improved preoperative screening methods for STUMP and sarcoma should be established.     

Prediction of Pregnancy Rate of In Vitro Fertilization and Embryo Transfer in Women Aged 40 and over with Basal Uterine Artery Pulsatility Index

Purpose: The purpose was to determine the effect of basaluterine perfusion on the pregnancy rates of in vitro fertilizationand embryo transfer (IVF-ET) in women aged 40 and above. Methods: A total of 47 patient aged 40 and over underwentIVF-ET. The conception cycles and the nonconception cycleswere compared. Results: Of the 47 patients, 4 patients were pregnant (8.5%).The mean age, basal follicle stimulating hormone (FSH),basal estradiol (E₂) level, antral follicle count (AFC), numberof ampoules of gonadotropin used, E₂ levels and endometrial thickness on the day of human chorionic gonadotropin(hCG) administration, number of retrieved and fertilizedoocytes, and number of transferred embryos were not statisticallysignificant between the conception and nonconceptioncycles. However, the basal uterine artery pulsatility index(UA PI) was significantly lower in the conception cycles(P < 0.001). The receiver operating characteristics (ROC)curve analysis for basal FSH, AFC, and basal UA PI inpredicting the pregnancy rate of IVF in patients aged 40were demonstrated. The best prediction rate was achievedby a pulsatility index cutoff of < 2.0 for a receptive uterus. Conclusions: Increased uterine perfusion in the early follicularphase enhanced the pregnancy rate of IVF in womenaged 40 and above. It is therefore essential that patientsaged 40 with poor basal uterine perfusion should beidentified early in the early follicular phase of the menstrualcycle to apply appropriate intervention to improve the uterinecirculation for the subsequent chance of pregnancy.     

Fine structure of human uterine muscle in pregnancy

The ultrastructure of the human uterine smooth muscle at mid- and full-term pregnancy was described and compared with that of nonpregnant uterus. The most striking finding was a progressive modification in the development and topographical relationships of the cytoplasmic organelles, especially the endoplasmic reticulum and Golgi complex. The possible relations between the modifications found and the functional abilities of uterine smooth muscle at pregnancy are discussed.     

小鼠子宫内膜着床期碱性成纤维细胞生长因子及其受体免疫组织化学观察

为进一步阐明碱性成纤维细胞生长因子 (basic fibroblast growth factor,b FGF)在胚泡着床中的生物学作用 ,本文采用免疫组织化学的方法检测了 b FGF及其受体在小鼠早期妊娠子宫中的分布状况。结果显示 :b FGF及其受体广泛分布于子宫内膜各种细胞中 ,其分布呈现出明显的阶段性变化。受精后 4～ 5 d,b FGF及其受体在子宫内膜上皮和腺上皮中呈阳性反应。随胚泡植入的进行 ,b FGF及其受体在蜕膜细胞中的表达逐渐增加 ,至受精后 d8达到高峰。结果提示 ,b FGF可能是小鼠胚泡着床过程中的一个重要调节因子     

Successful live birth after repeated high-dose radiotherapy to the uterus

Research questionIt has been established that radiotherapy can increase the risk of adverse pregnancy outcomes. However, there is currently no consensus on the effective sterilizing dose of adulthood uterine radiotherapy.DesignThis is a case report of a 36-year-old women with three different cancer types who received repeated high-dose radiotherapy of 66 Gy and 50 Gy to the pelvis. The study used a dose–volume histogram, the most widely used tool to calculate the radiation distribution within a volume of interest in a patient during radiotherapy. It was determined that the current patient's uterus might have received the highest uterine radiation dosage for full-term live birth that has been reported in the current literature.ResultsDue to iatrogenic ovarian failure, the woman was only able to use donor eggs. After preparation of the endometrium for 18 days, it had reached 8.7 mm in thickness with a triple-line appearance. Two cleavage-stage embryos were transferred, one of which implanted successfully. The course of the pregnancy was uneventful. Finally, the patient gave birth to a healthy baby via Caesarean section at 38⁺⁵ weeks of gestation.ConclusionsThe uterus may be more resistant to radiotherapy than previously understood. Uterine fertility preservation methods should be guided by the age of the patient receiving radiotherapy and the actual dose of radiation exposure of the uterus. Future studies should implement a dose–volume histogram to calculate the radiation exposure of the reproductive organs.     

Mechanism of action of sparteine sulfate on myometrial activity in vitro

The in vitro response of uterine muscle to sparteine sulfate was studied in 104 strips of human and 65 strips of rat uterine muscle. Sparteine sulfate influences the duration and frequency but not the maximum tension development of spontaneous activity in the rat myometrium. In all studies of electrically stimulated human and rat myometrium an increase of maximum tension was observed after sparteine sulfate stimulation. In the human no increase in sensitivity to sparteine sulfate was observed with advancing gestation. However, the gradual increase in sensitivity to Pitocin as pregnancy progresses has been observed by us as well as by several other investigators. The rat uterus, unlike the human uterus, exhibits an increased sensitivity to sparteine sulfate during advancing stages of pregnancy. A greater response is demonstrable during late pregnancy and is relatively refractile during early and midgestation. The response of muscle strips obtained from placental implantation sites to sparteine sulfate were less marked than uterine muscle strips from the opposite wall of the same uterus (nonplacental sites). Furthermore, the dose response range of human uterine muscle to increasing concentrations of sparteine sulfate was narrower than with Pitocin. Larger doses of sparteine sulfate produced myometrial contracture in normal Krebs' solution. Lower concentrations had a tendency to cause myometrial contracture on partially depolarized muscle. These studies suggest the major action of sparteine sulfate is directed at the cell membrane rather than directly on the contractile system of the uterine muscle cell.