Expression of nitric oxide synthase isoforms in pregnant human myometrium

β3 Receptor Signaling in Pregnant Human Myometrium Suggests a Role for β3 Agonists as Tocolytics

Preterm labor leading to preterm birth is the leading cause of infant morbidity and mortality. At the present time, nothing can reliably halt labor once it begins. The knowledge that agonists of the β2 adrenergic receptor relax airway smooth muscle and are effective in the treatment of asthma led to the notion that β2 mimetics would prevent preterm birth by relaxing uterine smooth muscle. The activation of cAMP-dependent protein kinase by β2 receptors is unable to provide meaningful tocolysis. The failure of β2 agonists such as ritodrine and terbutaline to prevent preterm birth suggests that the regulation of uterine smooth muscle is disparate from that of airway. Other smooth muscle quiescent-mediating molecules, such as nitric oxide, relax vascular smooth muscle in a cGMP-protein kinase G-dependent manner; however, nitric oxide activation of protein kinase G fails to explain the relaxation of the myometrium to nitric oxide. Moreover, nitric oxide-mediated relaxation is blunted in preterm labor, and thus, for this reason and because of the fall in maternal blood pressure, nitric oxide cannot be employed as a tocolytic. The β3 adrenergic receptor-mediated relaxation of the human myometrium is claimed to be cAMP-dependent protein kinase-dependent. This is scientifically displeasing given the failure of β2 agonists as tocolytics and suggests a non-canonical signaling role for β3AR in myometrium. The addition of the β3 agonist mirabegron to pregnant human myometrial strips in the tissue bath relaxes oxytocin-induced contractions. Mirabegron stimulates nitric oxide production in myometrial microvascular endothelial cells, and the relaxation of uterine tissue in vitro is partially blocked by the addition of the endothelial nitric oxide synthase blocker Nω-Nitro-L-arginine. Recent data suggest that both endothelial and smooth muscle cells respond to β3 stimulation and contribute to relaxation through disparate signaling pathways. The repurposing of approved medications such as mirabegron (Mybetriq™) tested in human myometrium as uterine tocolytics can advance the prevention of preterm birth.

Gasotransmitters in pregnancy: from conception to uterine involution

Gasotransmitters are endogenous small gaseous messengers exemplified by nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S or sulfide). Gasotransmitters are implicated in myriad physiologic functions including many aspects of reproduction. Our objective was to comprehensively review basic mechanisms and functions of gasotransmitters during pregnancy from conception to uterine involution and highlight future research opportunities. We searched PubMed and Web of Science databases using combinations of keywords nitric oxide, carbon monoxide, sulfide, placenta, uterus, labor, and pregnancy. We included English language publications on human and animal studies from any date through August 2018 and retained basic and translational articles with relevant original findings. All gasotransmitters activate cGMP signaling. NO and sulfide also covalently modify target protein cysteines. Protein kinases and ion channels transduce gasotransmitter signals, and co-expressed gasotransmitters can be synergistic or antagonistic depending on cell type. Gasotransmitters influence tubal transit, placentation, cervical remodeling, and myometrial contractility. NO, CO, and sulfide dilate resistance vessels, suppress inflammation, and relax myometrium to promote uterine quiescence and normal placentation. Cervical remodeling and rupture of fetal membranes coincide with enhanced oxidation and altered gasotransmitter metabolism. Mechanisms mediating cellular and organismal changes in pregnancy due to gasotransmitters are largely unknown. Altered gasotransmitter signaling has been reported for preeclampsia, intrauterine growth restriction, premature rupture of membranes, and preterm labor. However, in most cases specific molecular changes are not yet characterized. Nonclassical signaling pathways and the crosstalk among gasotransmitters are emerging investigation topics.

High Altitude Reduces NO-Dependent Myometrial Artery Vasodilator Response During Pregnancy

The chronic hypoxia of high-altitude (HA) residence reduces uterine artery blood flow during pregnancy, likely contributing to an increased frequency of preeclampsia and intrauterine growth restriction. We hypothesized that this lesser pregnancy blood flow rise was due, in part, to reduced vasodilation of myometrial arteries (MAs). Here, we assessed MA vasoreactivity in healthy residents of high (2902±39 m) or low altitude (LA; 1669±10 m). MA contractile responses to potassium chloride, phenylephrine, or the thromboxane A2 agonist U46619 did not differ between LA and HA women. Acetylcholine vasodilated phenylephrine or U466119 preconstricted MAs at LA, yet had no effect on HA MAs. In contrast, another vasodilator, bradykinin, relaxed MAs from both altitudes similarly. At LA, the NO synthase inhibitor L-N^G-nitroarginine methyl ester decreased both acetylcholine and bradykinin vasodilation by 56% and 33%, respectively. L-N^G-nitroarginine methyl ester plus the COX (cyclooxygenase) inhibitor indomethacin had similar effects on acetylcholine and bradykinin vasodilation (68% and 42% reduction, respectively) as did removing the endothelium (78% and 50% decrease, respectively), suggesting a predominantly NO-dependent vasodilation at LA. However, at HA, L-N^G-nitroarginine methyl ester did not change bradykinin vasodilation, whereas indomethacin or endothelium removal decreased it by 28% and 72%, respectively, indicating impaired NO signaling at HA. Suggesting that the impairment was downstream of eNOS (endothelial NO synthase), HA attenuated the vasodilation elicited by the NO donor sodium nitroprusside. We concluded that reduced NO-dependent MA vasodilation likely contributes to diminished uteroplacental perfusion in HA pregnancies.

The effect of the release of exogenous nitric oxide on the responses of the pregnant human myometrium to oxytocin

OBJECTIVE

Introduction: Currently there is insufficient evidence to support the routine administration of nitric oxide donors in the treatment of threatened preterm labor. An understanding of the role that nitric oxide plays in the management of threatened preterm labor may lead to more effective treatment and prevention. The aim of our study was to examine the involvement of exogenous nitric oxide release in regulating responses of the human pregnant myometrium to oxytocin.

PATIENTS AND METHODS

Material and methods: Biopsies of human myometrial tissue during pregnancy were obtained from 8 pregnant women, aged 21-35 years. The responses of the specimens to oxytocin in the absence and presence of a DETA/NO were recorded under isometric conditions. Preincubation with exogenous nitric oxide significantly (p<0.001) attenuated the contractile response of the uterine strips to oxytocin in concentrations higher than 10-8 mol/L.

RESULTS

Results: The inhibition of nitric oxide synthesis alone or in combination with DETA/NO incubation did not significantly change the oxytocin contractile effect in the concentration-response curve. Moreover, there was no significant variation in the mean value for log EC50 for oxytocin between the group with oxytocin alone and other groups.

CONCLUSION

Conclusions: We present evidence in support of the hypothesis that continuous nitric oxide supply to the human pregnant myometrium environment attenuates its response to oxytocin but only when endogenous production of nitric oxide is not impaired.

Comparison of maternal omentin-1 levels and genetic variability between spontaneous term and preterm births

OBJECTIVE

To determine maternal omentin-1 levels and genetic variability in the omentin-1 gene in women with spontaneous term and preterm births (PTBs).

MATERIALS AND METHODS

Maternal serum omentin-1 levels and the role of the omentin-1 Val109Asp (rs2274907) polymorphism were evaluated in 32 women with spontaneous term birth (sTB) and 30 women with spontaneous preterm birth (sPTB) including women with (n = 16) and without (n = 14) preterm premature rupture of membranes (PPROM).

RESULTS

Maternal omentin-1 levels were significantly lower in women with sPTBs compared to term births during the hospitalization period (p = .015). However, maternal omentin-1 levels were similar in women with sPTBs with and without PPROM (p = .990). Furthermore, the omentin-1 Val109Asp polymorphism was found to have no significant effect on omentin-1 serum levels. In addition, no significant differences in genotype distributions and allelic frequencies between sTB and sPTB were established.

CONCLUSIONS

High omentin-1 levels in normal sTBs compared to PTBs without significant differences between cases with and without PPROM suggest that omentin-1 plays a potential role in the pathophysiology of PTB but not in the PPROM mechanism itself.

Characterization of the myometrial transcriptome in women with an arrest of dilatation during labor

OBJECTIVE

The molecular basis of failure to progress in labor is poorly understood. This study was undertaken to characterize the myometrial transcriptome of patients with an arrest of dilatation (AODIL).

STUDY DESIGN

Human myometrium was prospectively collected from women in the following groups: (1) spontaneous term labor (TL; n=29) and (2) arrest of dilatation (AODIL; n=14). Gene expression was characterized using Illumina® HumanHT-12 microarrays. A moderated Student's t-test and false discovery rate adjustment were used for analysis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) of selected genes was performed in an independent sample set. Pathway analysis was performed on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database using Pathway Analysis with Down-weighting of Overlapping Genes (PADOG). The MetaCore knowledge base was also searched for pathway analysis.

RESULTS

(1) Forty-two differentially expressed genes were identified in women with an AODIL; (2) gene ontology analysis indicated enrichment of biological processes, which included regulation of angiogenesis, response to hypoxia, inflammatory response, and chemokine-mediated signaling pathway. Enriched molecular functions included transcription repressor activity, heat shock protein (Hsp) 90 binding, and nitric oxide synthase (NOS) activity; (3) MetaCore analysis identified immune response chemokine (C-C motif) ligand 2 (CCL2) signaling, muscle contraction regulation of endothelial nitric oxide synthase (eNOS) activity in endothelial cells, and triiodothyronine and thyroxine signaling as significantly overrepresented (false discovery rate <0.05); (4) qRT-PCR confirmed the overexpression of Nitric oxide synthase 3 (NOS3); hypoxic ischemic factor 1A (HIF1A); Chemokine (C-C motif) ligand 2 (CCL2); angiopoietin-like 4 (ANGPTL4); ADAM metallopeptidase with thrombospondin type 1, motif 9 (ADAMTS9); G protein-coupled receptor 4 (GPR4); metallothionein 1A (MT1A); MT2A; and selectin E (SELE) in an AODIL.

CONCLUSION

The myometrium of women with AODIL has a stereotypic transcriptome profile. This disorder has been associated with a pattern of gene expression involved in muscle contraction, an inflammatory response, and hypoxia. This is the first comprehensive and unbiased examination of the molecular basis of an AODIL.

Anandamide induces sperm release from oviductal epithelia through nitric oxide pathway in bovines

Mammalian spermatozoa are not able to fertilize an egg immediately upon ejaculation. They acquire this ability during their transit through the female genital tract in a process known as capacitation. The mammalian oviduct acts as a functional sperm reservoir providing a suitable environment that allows the maintenance of sperm fertilization competence until ovulation occurs. After ovulation, spermatozoa are gradually released from the oviductal reservoir in the caudal isthmus and ascend to the site of fertilization. Capacitating-related changes in sperm plasma membrane seem to be responsible for sperm release from oviductal epithelium. Anandamide is a lipid mediator that participates in the regulation of several female and male reproductive functions. Previously we have demonstrated that anandamide was capable to release spermatozoa from oviductal epithelia by induction of sperm capacitation in bovines. In the present work we studied whether anandamide might exert its effect by activating the nitric oxide (NO) pathway since this molecule has been described as a capacitating agent in spermatozoa from different species. First, we demonstrated that 1 µM NOC-18, a NO donor, and 10 mM L-Arginine, NO synthase substrate, induced the release of spermatozoa from the oviductal epithelia. Then, we observed that the anandamide effect on sperm oviduct interaction was reversed by the addition of 1 µM L-NAME, a NO synthase inhibitor, or 30 µg/ml Hemoglobin, a NO scavenger. We also demonstrated that the induction of bull sperm capacitation by nanomolar concentrations of R(+)-methanandamide or anandamide was inhibited by adding L-NAME or Hemoglobin. To study whether anandamide is able to produce NO, we measured this compound in both sperm and oviductal cells. We observed that anandamide increased the levels of NO in spermatozoa, but not in oviductal cells. These findings suggest that anandamide regulates the sperm release from oviductal epithelia probably by activating the NO pathway during sperm capacitation.

Nitric oxide detection by DAF (diaminofluorescein) fluorescence in human myometrial tissue

Nitric oxide (NO) is considered to be involved in the modulation of uterine contractility. In the present pilot study, the direct detection of intracellular NO in pregnant human myometrial tissues has been investigated by using the fluorescent indicator 4,5-diaminofluorescein-2 diacetate (DAF-2DA). Pregnant myometrial tissue samples were obtained during Cesarean sections between week 34 and 40 of gestation before the onset of labor. Living explants were loaded with 10 microM DAF-2DA, stimulated with 1 mM arginine, subsequently fixed with glutaraldehyde and examined by fluorescence microscopy. The presence of NO synthases (NOS) was studied by immunohistochemistry. After application of DAF-2DA, DAF fluorescence was located primarily in blood vessels and to a minor extent in myometrial cells. By immunohistochemistry, strong endothelial NOS (eNOS) staining was found in vessel walls. In myometrial cells weak staining of eNOS and inducible NOS was observed. We conclude that the direct NO detection by DAF-2DA provides a new and independent method to identify sites of NO production in myometrium and other heterogeneous tissues.

Nongenomic, endothelium-independent effects of estrogen on human coronary smooth muscle are mediated by type I (neuronal) NOS and PI3-kinase-Akt signaling

Sex steroids exert profound and controversial effects on cardiovascular function. For example, estrogens have been reported to either ameliorate or exacerbate coronary heart disease. Although estrogen dilates coronary arteries from a variety of species, the molecular basis for this acute, nongenomic effect is unclear. Moreover, we know very little of how estrogen affects human coronary artery smooth muscle cells (HCASMC). The purpose of this study was to elucidate nongenomic estrogen signal transduction in HCASMC. We have used tissue (arterial tension studies), cellular (single-channel patch clamp, fluorescence), and molecular (protein expression) techniques to now identify novel targets of estrogen action in HCASMC: type I (neuronal) nitric oxide synthase (nNOS) and phosphatidylinositol 3-kinase (PI3-kinase)Akt. 17beta-Estradiol (E(2)) increased NO-stimulated fluorescence in HCASMC, and cell-attached patch-clamp experiments revealed that stimulation of nNOS leads to increased activity of calcium-activated potassium (BK(Ca)) channels in these cells. Furthermore, overexpression of nNOS protein in HCASMC greatly enhanced BK(Ca) channel activity. Immunoblot studies demonstrated that E(2) enhances Akt phosphorylation in HCASMC and that wortmannin, an inhibitor of PI3-kinase, attenuated E(2)-stimulated channel activity, NO production, Akt phosphorylation, and estrogen-stimulated coronary relaxation. These studies implicate the PI3-kinase/Akt signaling axis as an estrogen transduction component in vascular smooth muscle cells. We conclude, therefore, that estrogen opens BK(Ca) channels in HCASMC by stimulating nNOS via a transduction sequence involving PI3-kinase and Akt. These findings now provide a molecular mechanism that can explain the clinical observation that estrogen enhances coronary blood flow in patients with diseased or damaged coronary arteries.

Sarcomas often express constitutive nitric oxide synthases (NOS) but infrequently inducible NOS

Nitric oxide (NO) has a dual action in tumors, with both pro-tumor and anti-tumor activities. NO is produced by nitric oxide synthases (NOS). There are three enzyme isoforms: two of them are constitutively produced (neuronal or brain NOS and endothelial NOS), and one is an inducible form (iNOS). NOS expression has been shown in several epithelial tumors, but there is no report addressing NOS expression in sarcomas. The authors evaluated the expression of NOS in 97 cases of various sarcomas spotted in duplicate in a tissue array paraffin block. Eighty-four of the 97 tumor specimens (86.6%) expressed nNOS, and most of them showed a strong expression of the isoenzyme. Only chondrosarcomas and liposarcomas had significant numbers of negative cases, and all pleomorphic sarcomas, alveolar soft part sarcomas, angiosarcomas, gastrointestinal stromal tumors, and synovial sarcomas showed some degree of positivity. Forty-three cases (44.4%) showed eNOS immunostaining, but only 15.5% showed a strong signal, with emphasis on angiosarcomas, chondrosarcomas, alveolar soft part sarcomas, and synovial sarcoma. Strong expression of iNOS was observed in only 9 cases (9.3%), with weak expression in another 26 cases (26.8%). Strong expression of iNOS was found in malignant peripheral nerve sheet tumors, liposarcomas, pleomorphic sarcomas, fibrosarcomas, chondrosarcomas, and synovial sarcomas. Apparently alveolar soft part sarcomas are unusual in their capacity of expression of NOS isoforms, and in a very peculiar pattern. In conclusion, sarcomas in general commonly express constitutive NOS, and only a few types of sarcomas can express iNOS, the isoenzymes capable of releasing large amounts of NO. More comprehensive studies should be performed to better understand the clinical importance of NOS expression and NO production in sarcomas.

ORIGINAL RESEARCH—BASIC SCIENCE: Intracavernosal Basic Fibroblast Growth Factor Improves Vasoreactivity in the Hypercholesterolemic Rabbit

PURPOSE

We determined the effects of intracavernosal injection (ICI) of recombinant basic fibroblast growth factor (rbFGF) on corporal tissue in hypercholesterolemic rabbits.

METHODS

Twenty New Zealand White rabbits were fed a 1% cholesterol diet for 6 weeks and were randomly divided into four groups. Group 1 (N = 5) received an ICI of phosphate buffered saline solution (PBS) once and again 3 weeks later. Group 2 (N = 4) received an ICI of 2.5 microg rbFGF once and PBS 3 weeks later. Group 3 (N = 6) received an ICI of 2.5 microg rbFGF once and again 3 weeks later. Group 4 (N = 5) received an ICI of 2.5 microg rbFGF once. All animals were maintained on the high cholesterol diet until sacrifice, 3 weeks after last injection. Strips of corporal tissue were submaximally contracted with norepinephrine, and dose-response curves were generated to evaluate endothelial-dependent (acetylcholine, ACH) and endothelial-independent (sodium nitroprusside, SNP) vasoreactivity. Protein levels of bFGF and vascular endothelial growth factor (VEGF) were assessed by enzyme-linked immunosorbent assay. Neuronal nitric oxide synthase (nNOS) protein and mRNA were detected by Western blot and semi-quantitative polymerase chain reaction, respectively.

RESULTS

Vasoreactivity was improved by bFGF treatment as shown by higher ED50[-log(M)] of ACH and SNP in Groups 2, 3, and 4. The expression of bFGF protein, VEGF protein, nNOS protein, and mRNA were all increased after bFGF treatment.

CONCLUSIONS

ICI of bFGF improved vasoreactivity in hypercholesterolemic rabbit corporal tissue, offering a new direction to explore for the treatment of erectile dysfunction.

Estrogen-induced contraction of coronary arteries is mediated by superoxide generated in vascular smooth muscle

Although previous studies demonstrated beneficial effects of estrogen on cardiovascular function, the Women's Health Initiative has reported an increased incidence of coronary heart disease and stroke in postmenopausal women taking hormone replacement therapy. The objective of the present study was to identify a molecular mechanism whereby estrogen, a vasodilatory hormone, could possibly increase the risk of cardiovascular disease. Isometric contractile force recordings were performed on endothelium-denuded porcine coronary arteries, whereas molecular and fluorescence studies identified estrogen signaling molecules in coronary smooth muscle. Estrogen (1-1,000 nM) relaxed arteries in an endothelium-independent fashion; however, when arteries were pretreated with agents to uncouple nitric oxide (NO) production from NO synthase (NOS), estrogen contracted coronary arteries with an EC(50) of 7.3 +/- 4 nM. Estrogen-induced contraction was attenuated by reducing superoxide (O(2)(-)). Estrogen-stimulated O(2)(-) production was detected in NOS-uncoupled coronary myocytes. Interestingly, only the type 1 neuronal NOS isoform (nNOS) was detected in myocytes, making this protein a likely target mediating both estrogen-induced relaxation and contraction of endothelium-denuded coronary arteries. Estrogen-induced contraction was completely inhibited by 1 muM nifedipine or 10 muM indomethacin, indicating involvement of dihydropyridine-sensitive calcium channels and contractile prostaglandins. We propose that a single molecular mechanism can mediate the dual and opposite effect of estrogen on coronary arteries: by stimulating type 1 nNOS in coronary arteries, estrogen produces either vasodilation via NO or vasoconstriction via O(2)(-).

Expression of iNOS mRNA and inhibitory effect of NO on uterine contractile activity in rats are determined by local rather than systemic factors of pregnancy

Our purpose was to investigate whether the local or systemic factors of pregnancy are associated with inducible nitric oxide synthase (iNOS) mRNA expression and to determine the inhibitory effects of pharmacological agents that increase cGMP levels in rat myometrium. iNOS mRNA expression was determined in uterine tissues from nonpregnant rats and on day 17 of gestation in the pregnant and non-pregnant uterine horns by RT-PCR. In addition, uterine rings from the pregnant and non-pregnant uterine horns were placed in Krebs-Henseleit solution for isometric recordings of spontaneous contractions. Concentration-inhibition relationships to diethylamine/nitric oxide complex, 8-bromo-cGMP, and the selective phosphodiesterase V inhibitor were obtained. Compared to nonpregnant rats, expression of iNOS mRNA in myometrium increased during pregnancy, which was maximal on day 17, followed by a decrease on day 21 of gestation. Expression of iNOS mRNA at day 17 of gestation was greater in pregnant uterine horns than in nonpregnant ones. Maximal inhibition of phosphodiesterase V and increasing cGMP induced similar inhibition of spontaneous contractions in nonpregnant and pregnant uterine horns, while NO induced less inhibition in the former. The results suggest that the local pregnancy factor is needed for signal transduction from NO to soluble guanylate cyclase at a time when maximal expression of iNOS mRNA is evident.

Inhibition of calcium-calmodulin kinase restores nitric oxide production and signaling in submandibular glands of a mouse model of salivary dysfunction

Nitric oxide is an intracellular and diffusible messenger of neurotransmitters involved in salivary secretion, as well as an inflammatory mediator in salivary gland diseases. It is synthesized by three different isoforms of nitric oxide synthase (NOS), each subject to a fine transcriptional, post-transcriptional and/or post-translational regulation. Our purpose was to study the possible mechanisms leading to NOS downregulation in submandibular glands of normal mice and in the nonobese diabetic (NOD) mouse model of salivary dysfunction with lower NOS activity. NOS activity and cGMP accumulation were determined by radioassays in submandibular glands of both mice in the presence of the protein kinase inhibitors KN-93 and bisindolylmaleimide. NOS I mRNA and protein expression and localization were assessed by RT-PCR, Western blot and immunohistochemistry. A downregulatory effect of calcium-calmodulin kinase II (CaMK II) on NOS activity in submandibular glands of both NOD and BALB/c mice was observed. Our results are consistent with a physiological regulation of NOS activity by this kinase but not by PKC in normal BALB/c mice. They are also supportive of a role for CaMK II in the lack of detectable NOS activity in submandibular glands of NOD mice. KN-93 also restored cGMP accumulation in NOD submandibular glands. The downregulation of NOS in NOD mice seems to be mainly mediated by this kinase rather than the result of a lower expression or different cellular localization of the enzyme. It was not related to different substrate or cofactors availability either.

Expression of inducible nitric oxide synthase messenger RNA, but not guanylate cyclase messenger RNA, depends on gestational age in rat myometrium

We studied the expression of inducible nitric oxide (NO) synthase (iNOS) and soluble guanylate cyclase (sGC) mRNAs in pregnant rat myometrium. Expression of iNOS and sGC alpha1, beta1 and beta2 mRNA was analyzed in non-pregnant and pregnant (days 10, 14, 17 and 21) Wistar rats by reverse transcription-polymerase chain reaction. Expression of iNOS mRNA increased during pregnancy but decreased on day 21 of gestation. Expression of GC alpha1 mRNA was greater than GC beta1 mRNA at all time points. Expression of uterine GC alpha1 and GC beta1 mRNA did not change significantly during pregnancy and did not differ significantly from non-pregnant levels. The values of sGC beta2 mRNA were below the limit of detection. In conclusion, the expression of iNOS mRNA increased during pregnancy in the myometrium and decreased at term, while the expression of sGC mRNA was not affected by pregnancy. Thus, it is the changes in NO production, rather than changes in its target, that are responsible for uterine quiescence during pregnancy and initiation of labor.

Regulation of uterine function: a biochemical conundrum in the regulation of smooth muscle relaxation

Premature birth accounts for the majority of fetal morbidity and mortality in the developed world and is disproportionately represented in some populations, such as African Americans in the United States. The costs associated with prematurity are staggering in both monetary and human terms. Present therapeutic approaches for the treatment of labor leading to preterm delivery are inadequate and our understanding of the regulation of myometrial smooth muscle contraction-relaxation is incomplete. The ability of nitric oxide to relax smooth muscle has led to an interest in employing nitric oxide-donors in the treatment of preterm labor. Fundamental differences exist, however, in the regulation of uterine smooth muscle relaxation and that of other smooth muscles and constitute a conundrum in our understanding. We review the evidence that nitric oxide-mediated relaxation of myometrial smooth muscle, unlike vascular or gastrointestinal smooth muscle, is independent of global elevation of cyclic guanosine 5'-monophosphate. Applying our current understanding of microdomain signaling and taking clues from genomic studies of pregnancy, we offer a framework in which to view the apparent conundrum and suggest testable hypotheses of uterine relaxation signaling that can explain the mechanistic distinctions. We propose that understanding these mechanistic distinctions in myometrium will reveal molecular targets that are unique and thus may be explored as therapeutic targets in the development of new uterine smooth muscle-specific tocolytics.

Prostaglandins and the myometrium and cervix

Prostaglandins have long been thought to play important roles in the mechanism of parturition. Here we review the involvement of prostaglandins in myometrial and cervical functions with emphasis on human labor and birth. In addition, the cellular sources of prostaglandins as well as their interactions with various other endocrine, paracrine and physical factors, such as oxytocin, corticotropin releasing hormone, nitric oxide, platelet activating factor, cytokines, endothelin and stretch are also addressed together with their potential role in the molecular reorganization of cervical structure associated with labor and delivery. Finally, the premier role of progesterone in pregnancy maintenance and parturition is juxtaposed with the proposed "fine-tuning", modulatory role of prostaglandins and the above listed factors in the regulation of parturition.

Endothelial endostatin release is induced by general cell stress and modulated by the nitric oxide/cGMP pathway

Endostatin is a 20 kDa carboxyl-terminal fragment of collagen XVIII that, when added exogenously, inhibits endothelial proliferation and migration in vitro and angiogenesis and tumor growth in vivo. Previous results showed endostatin/collagen XVIII labeling in few endothelial cells in human glioblastoma multiforme. We have now observed constitutive release of endostatin from one of four endothelial cell lines. Induction of endostatin release was observed after H2O2, an in vitro model of cell stress, CoCl2, a model of hypoxia, and by IFN-gamma challenge. Endostatin expression and release was reduced by the nitric oxide synthase inhibitors aminoguanidine and L-NAME and induced by the NO synthase-independent NO donors sodium nitroprusside (SNP) and spermine-NONO-ate. SNP-mediated endostatin induction was abrogated by the soluble guanylate cyclase inhibitor 1H-(1.2.4) oxadiazolo (4,3-A) quinoxalin-1-one. Adenoviral endostatin transduction resulted in the release of endostatin from endothelial cells and in down-regulation of iNOS (NOS2) and eNOS (NOS3), and surprisingly in a 10% induction of PCNA. These results describe the modulation of endostatin release by the NO signaling cascade and provide important new pharmacological information for the systemic induction of endogenous endostatin release by common NO donor pharmacotherapy.

FGL2 prothrombinase messenger RNA expression in gravid and nongravid human myometrium

OBJECTIVE

Thrombin is a potent uterotonic agent that may play an important role in human parturition. FGL2 is a prothrombinase that cleaves prothrombin to thrombin. The purpose of this study was to determine FGL2 messenger RNA expression in human myometrium and to assess its relationship to the expression of EP3-6 prostaglandin receptor and inducible nitric oxide synthase.

STUDY DESIGN

Myometrium was obtained from gravid women who underwent cesarean delivery (n = 19), from premenopausal (n = 10) and menopausal (n = 10) women who underwent hysterectomy, and from nonpregnant women who received 200 mg of misoprostol vaginally 12 hours before hysterectomy (n = 8). FGL2 messenger RNA expression was determined with the use of semiquantitative polymerase chain reaction and was compared with previously determined messenger RNA expression levels for EP3-6 and inducible nitric oxide synthase for the same samples. Statistical analysis was performed with the use of independent t test, Fisher exact test, analysis of variance, and linear regression, where appropriate.

RESULTS

All samples that were analyzed contained demonstrable quantities of FGL2 messenger RNA. The highest FGL2 expression was found in gravid women, followed by women who were treated with misoprostol, by premenopausal nonpregnant women, and by menopausal women (P <.0001, analysis of variance). Significantly higher levels of FGL2 expression were found in the gravid women compared with the women who were treated with misoprostol (P <.001), the premenopausal nonpregnant women (P <.001), and the menopausal women (P <.0001). FGL2 messenger RNA expression correlated with EP3-6 and inducible nitric oxide synthase expression in all samples combined (r = 0.55, P <.0001; and r = 0.67, P <.001, respectively).

CONCLUSION

The expression of FGL2 messenger RNA is increased in gravid myometrium compared with nonpregnant samples. Its expression significantly correlates to EP3-6 and inducible nitric oxide synthase expression. FGL2 prothrombinase expression may mediate the role of thrombin in human parturition.

Regulation of connexin 43 by nitric oxide in primary uterine myocytes from term pregnant women

OBJECTIVE

Our purpose was to test the hypothesis that nitric oxide signals regulate the expression of the gap-junction protein connexin 43 in primary uterine myocytes from pregnant women at term.

STUDY DESIGN

Northern analysis and immunoblotting were used to determine the expression of connexin 43 in myocytes cultured in the presence of the nitric oxide donors S -nitroso-N -acetyl-penicillamine (SNAP) (100 micromol/L) and (Z)-1-[2-(2-aminoethyl)-N -(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate diethylenetriamine (NOC-18) (100 micromol/L). We also tested the effect of the NO stimulants 8-bromo-cyclic adenosine 3',5'-monophosphate (cAMP) (100 micromol/L) and 8-bromo-cyclic guanosine 3',5'-monophosphate (cGMP) (200 micromol/L), and the nitric oxide synthase inhibitors N -nitro-L-arginine methyl ester (NAME) (100 micromol/L) and L -N (1-iminoethyl)lysine (NIL) (50 micromol/L).

RESULTS

Nitric oxide and 8-bromo-cAMP reduced the level of connexin 43 expression, and 8-bromo-cGMP had no effect. In contrast, NIL, but not NAME, increased the levels of connexin 43 protein without affecting the level of connexin 43 messenger RNA. With immunoblotting, expression of inducible nitric oxide synthase was not detected in these cells.

CONCLUSION

Nitric oxide down-regulates the expression of connexin 43 in cultured human myocytes. We speculate that this effect may decrease the efficacy of intermyocyte signaling and thus contribute to uterine quiescence during human pregnancy.

The expression of EP3-6 and inducible nitric oxide synthase messenger RNA are correlated in pregnant and misoprostol-treated but not in nongravid or menopausal myometrium

OBJECTIVE

Our purpose was to investigate the expression level of inducible nitric oxide synthase (iNOS) in nongravid and gravid human myometrium and assess its relation to the expression of EP3 prostaglandin receptor isoforms.

STUDY DESIGN

Myometrial tissue from a cohort of gravid, nongravid, and menopausal subjects and from nongravid subjects exposed to misoprostol was obtained and analyzed for iNOS messenger RNA (mRNA) expression and compared with previously determined mRNA levels for the EP3-6 prostaglandin receptor from the same samples by means of semiquantitative polymerase chain reaction.

RESULTS

Significantly higher levels of iNOS mRNA expression were found in the gravid compared with premenopausal nongravid (P <.02) and menopausal (P <.05,) samples. Linear regression analysis of iNOS versus EP3-6 expression showed a positive correlation between all studied samples (n = 47, P <.0001, r = 0.815). Among individual groups, a significant linear correlation was found only in pregnant (n = 10, P <.0001, r = 0.785) and misoprostol-exposed (n = 7, P =.0256, r = 0.815) subjects. No correlation between iNOS and EP3-6 mRNA levels was noted in the nongravid premenopausal groups (n = 10, P =.205, r = 0.350), although a nonsignificant trend was found for the menopausal group (n = 10, P =.0535, r = 0.624). When the data from pregnant patients were stratified, both laboring and nonlaboring women displayed the observed correlation (n = 6, P <.0001, r = 0.993; and n = 13, P =.008, r = 0.697, respectively).

CONCLUSION

iNOS and EP3-6 expression are strongly correlated in gravid and misoprostol-treated, nongravid myometrium.

Up-regulation of nitric oxide synthase and modulation of the guanylate cyclase activity by corticotropin-releasing hormone but not urocortin II or urocortin III in cultured human pregnant myometrial cells

The biological actions of corticotropin-releasing hormone (CRH) in the human myometrium during pregnancy and labor are unknown. We hypothesized that CRH may modulate the nitric oxide system, and influence myometrial relaxation/contractility. Incubation of myometrial cells with CRH, but not urocortin II or urocortin III, for 8-16 h significantly induced mRNA and protein expression of endothelial and brain but not inducible nitric oxide synthase (NOS) isoforms. This action resulted in increased activity of soluble guanylate cyclase (GC(s)), demonstrated by the enhanced cGMP-producing capacity of the NO donor, sodium nitroprusside. CRH also caused acute activation of the membrane-bound GC, shown by increased basal or atrial natriuretic peptide (ANP)-stimulated cGMP production. These effects appeared to be mediated via the R1 receptors because the CRH receptor antagonists, astressin and antalarmin but not anti-sauvagine 30, could block them. The acute effects of CRH were significantly reduced by inhibition of protein kinase A (PKA) activity, suggesting it is partially PKA dependent. Activation of protein kinase C (PKC) resulted in significant inhibition of both ANP-and CRH-stimulated cGMP production, suggesting a direct effect of PKC on membrane-bound GC. In conclusion, CRH appears to have a dual effect on myometrial NOS/GC pathway, a short term effect predominantly mediated by PKA, and a long-term effect increasing constitutive NOS expression, mediated by a PKA-independent mechanism. This mechanism could potentially be active during human pregnancy, and, because cGMP stimulates myometrial relaxation, these findings further suggest that during pregnancy CRH primarily activates intracellular signals that contribute to the maintenance of myometrial quiescence.