Rat myometrial smooth muscle cells express endothelial nitric oxide synthase

Relaxant Effects of the Aqueous Extract of Excoecaria grahamii (Euphorbiaceae) Leaves on Uterine Horn Contractility in Wistar Rats

In uterine smooth muscle, the effects of Excoecaria grahamii are not yet documented. To fill this gap, we investigated the pharmacological effect of Excoecaria grahamii on the contraction of the rat isolated uterine horns. The isolated segments were exposed to different concentrations of the aqueous extract of Excoecaria grahamii leaves and pharmacological drugs. The results showed that Excoecaria grahamii aqueous extract decreased the amplitude and frequency by concentration-related manner. IC50 values were 2.4 and 2.6, respectively, for amplitude and frequency. Our study revealed that the extract did not act through histamine H2-receptors or the nitric oxide pathway. It also inhibited uterine contractions induced by oxytocin and potassium chloride (KCl). These data suggest that Excoecaria grahamii active compound can be used for calming uterine contractions. The action of Excoecaria grahamii showed that it can be useful to fight against diseases which caused uterotonic effects. It can be useful to prevent preterm birth and pains caused by menstruations but further investigation is needed to clarify the mechanism action.

The role of nitric oxide in the effects of ovarian steroids on spontaneous myometrial contractility in rats

Forty ovariectomized rats were apportioned into one control and three experimental groups (n=10 each) to evaluate the role of nitric oxide in the effects of ovarian steroids on spontaneous myometrial contractility in rats. The control group (group Ov) received sesame oil once daily for 10 days, whereas rats in the experimental groups were treated with progesterone (2 mg/(rat day); group P), 17beta-estradiol (10 microg/(rat day); group E2), or progesterone and 17beta-estradiol together (group E2+P). The functionality of the arginine-nitric oxide synthase (NOS)-nitric oxide (NO) pathway in the uterine horns of sacrificed rats was evaluated in an isolated organ bath. L-Arginine, sodium nitroprusside (SNP) and 8-Br-cGMP decreased uterine contractile tension induced by electric field stimulation (EFS) in the Ov, P, and E2+P groups, but not in the E2 group. In addition, L-arginine was ineffective when applied together with a NOS inhibitor, L-nitro-N-arginine (L-NNA). The percentage of contractile inhibition was higher in the Ov and P groups compared to the E2+P group. Immunohistochemical evaluation revealed that expression of neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS) in smooth muscles and nerve cells did not differ among the groups. Expression of nNOS and eNOS was strongly evident in the E2 and E2+P groups at both surface and glandular epithelium of the endometrium. iNOS expression was increased in surface epithelium of the E2 and E2+P groups. However, iNOS expression was only increased in glandular epithelial cells of the E2+P group. In conclusion, the L-arginine-NOS-NO pathway inhibits myometrial contractions via cGMP-dependent and -independent mechanisms, and while progesterone maintains the nitric oxide effects, estrogen prevents them. These results suggest that NOS does not mediate the effects of estrogen.

Epithelial invasion by Escherichia coli bearing Dr fimbriae is controlled by nitric oxide-regulated expression of CD55

We previously reported that inhibition of nitric oxide (NO) increases the rate of bacteremia and maternal mortality in pregnant rats with uterine infection by Escherichia coli expressing the Dr fimbria (Dr(+)). Epithelial binding and invasion by Dr(+) E. coli has also been shown to be dependent upon the expression level of the cellular receptor decay-accelerating factor (DAF; CD55). Here, we hypothesize that NO-related severity of infection could be mediated by changes in DAF expression and in the rate of epithelial invasion. The cellular basis of NO effects on epithelial invasion with Dr(+) E. coli was studied using Ishikawa endometrial carcinoma cells as an in vitro model of the human endometrial epithelium. Initially, we show that Ishikawa cells produce NO and express both NO synthase enzymes, NOS II and NOS III, and DAF protein. We next tested the abilities of both Dr(+) E. coli and a Dr(-) E. coli mutant to invade Ishikawa cells, and invasion was seen only with Dr(+) E. coli. Invasion by Dr(+) E. coli was decreased by elevated NO production and increased by NO inhibition. Elevated NO production significantly decreased DAF protein and mRNA expression in Ishikawa cells in a time- and dose-dependent manner. Here, we propose that in vitro invasion of an epithelial cell line is directly related to NO-regulated expression of DAF. The significance of NO-regulated receptor-ligand invasion is that it may represent a novel unrecognized phenomenon of epithelial defense against infection.

Localization of nitric oxide synthase type III in the internal thoracic and radial arteries and the great saphenous vein: a comparative immunohistochemical study

BACKGROUND

Endothelial nitric oxide synthase type III is the key enzyme of the nitric oxide production in the vessel wall. In this study the localization of endothelial nitric oxide synthase type III within the wall of the human internal thoracic and radial arteries and the great saphenous vein was investigated.

METHODS

Specimens were harvested from 23 patients undergoing surgical myocardial revascularization and submitted to light and electron microscope analysis using histochemical stainings and immunohistochemistry with specific antibodies anti-endothelial nitric oxide synthase type III, Factor VIII, and alpha-smooth muscle actin.

RESULTS

Endothelial nitric oxide synthase type III was evident in the intima of all conduits and, unexpectedly, in the muscle cells of the media of muscular internal thoracic arteries and radial arteries. No endothelial nitric oxide synthase type III expression was found in the media of great saphenous veins. Semiquantitative analysis revealed a higher endothelial nitric oxide synthase type III expression in the wall of internal thoracic artery, particularly at the level of the media.

CONCLUSION

Endothelial nitric oxide synthase type III is expressed in the intima of the internal thoracic and radial artery and the great saphenous vein and in the muscle cells of the media of the internal thoracic and radial arteries. However, the internal thoracic artery shows a higher intensity of endothelial nitric oxide synthase type III expression, particularly within the media. The present study provides the first demonstration of the endothelial nitric oxide synthase type III expression at the level of the smooth muscle cells of the tunica media of systemic human arteries and can provide an histologic explanation for the better results of the internal thoracic artery when used for coronary artery bypass grafting.

Nitric oxide synthesis in human nonpregnant myometrium and uterine myomas

OBJECTIVE

To clarify whether nitric oxide (NO) synthesis in myomas differs from that in parental human myometrium.

DESIGN

Prospective study.

SETTING

Academic research institution.

PATIENT(S)

Twenty-one patients undergoing laparoscopy or laparotomy for uterine myoma.

MAIN OUTCOME MEASURE(S)

Measurement of NO synthase activity in homogenates from myoma and parental myometrium biopsies, and NO synthesis assessment in cultured smooth-muscle cells.

RESULT(S)

Nitric oxide synthase activity in homogenates did not significantly differ between myoma and healthy myometrium. The medium taken from myoma cultures showed a significant increase in nitrite concentration compared with that taken from control myometrium cultures, but 24-hour incubation of both cell types with physiologic concentrations of 17beta-estradiol or progesterone did not significantly modify nitrite production.

CONCLUSION(S)

The maximal activity of NO synthase does not differ in myoma cells and in normal myometrial cells, but basal NO synthesis seems to be enhanced by an unknown signaling pathway that is not controlled by 17beta-estradiol or progesterone.

Steroid hormones augment nitric oxide synthase activity and expression in rat uterus

Nitric oxide (NO) is synthesized in a variety of tissues, including rat uterus, from L-arginine by NO synthase (NOS), of which there are three isoforms, namely neuronal, endothelial and inducible NOS (nNOS, eNOS and iNOS, respectively). Nitric oxide is an important regulator of the biology and physiology of the organs of the reproductive system, including the uterus. Some studies have shown increased variation in NO production and NOS expression during the oestrous cycle. However, the factors that regulate NO production in the uterus remain unclear. Therefore, in the present study, we investigated the effect of sex steroids on NOS expression and activity in the ovariectomized rat uterus. Ovariectomized rats received progesterone (4 mg per rat) or 17β-oestradiol (1 μg per rat). All rats were killed 18 h after treatment. Both progesterone and oestradiol were able to augment NOS activity. The effect of oestradiol was abolished by pre-incubation with 500 μM aminoguanidine, an iNOS inhibitor, or by coadministration of oestradiol with 3 mg kg−1 dexamethasone, but the effect of progesterone was not affected by these treatments. Uterine nNOS, eNOS and iNOS protein levels were assessed using Western blots. Ovariectomized rat uteri expressed iNOS and eNOS. Progesterone increased the expression of eNOS and iNOS, whereas oestradiol increased iNOS expression only. These results suggest that oestradiol and progesterone are involved in the regulation of NOS expression and activity during pregnancy and implantation in the rat.

New developments in the management of preterm labor

Current management of preterm labor has not changed the incidence of preterm delivery; therefore, significant research effort has been concentrated on the search for new methods of management. New tocolytics like inhibitors of cyclooxygenase 2 and nitric oxide donors have been tested in animal models and in preliminary clinical trials with promising results. Inhibition of cervical ripening may be one alternative to tocolysis. This new approach has a potential to be a valuable method of management of preterm labor if human studies confirm the promising results reported in animals. Growing evidence suggests that premature delivery may be associated with infection or fetal growth abnormalities, with dire consequences to the fetus. If these associations are to be included in risk and benefit assessment, then inhibition of preterm labor may prove to be detrimental to the fetus.

Expression of nitric oxide synthase isoforms in pregnant human myometrium

1. Endogenous nitric oxide has been proposed to play a role in the control of myometrial contractility in pregnancy. In this study, the expression, localisation and regulation of nitric oxide synthase (NOS) isoforms have been examined in human pregnant myometrium and cultured human myometrial smooth muscle cells, by immunoblotting, immunohistochemistry and reverse transcription-polymerase chain reaction. 2. Immunoblotting of extracts from freshly isolated myometrial tissue, affinity-enriched for NOS proteins by precipitation with ADP-sepharose, revealed expression of endothelial NOS (eNOS or NOS3) in tissues from preterm, term non-labour and active labour at term. Inducible NOS (iNOS or NOS2) and neuronal NOS (nNOS or NOS1) proteins were not detected at any stage of pregnancy. 3. Immunohistochemical detection showed that expression of eNOS protein was restricted to the endothelium of the myometrial vasculature, with no staining detected in myometrial smooth muscle cells. 4. Messenger RNA for all three NOS isoforms was detected, although iNOS and nNOS mRNAs were detectable only with high cycle number, implying a low copy number. 5. NOS isoforms were not detectable in human myometrial smooth muscle cells cultured from term non-labour pregnancies. Cytokine stimulation of cultured myometrial cells did not induce iNOS expression or nitrite accumulation in the culture medium, although both iNOS protein and nitrite release were detected in the human pulmonary epithelial cell line A549. 6. Levels of eNOS protein and of NOS mRNA expression were not correlated with gestational stage, suggesting that endogenously produced NO is not likely to be a modulator of myometrial tone during human pregnancy.

Nonpregnant sheep uterine type I and type III nitric oxide synthase expression is differentially regulated by estrogen

The aim of this study was to characterize the effect of estrogen on the expression of neuronal and endothelial isoforms of nitric oxide (NO) synthase (NOS) in myometrium, endometrium, and caruncle (nonglandular endometrium) in nonpregnant sheep. Twenty sheep were castrated during synchronized estrus (Days 14-16) and 4 days after surgery treated i.v. through the jugular with 100 microg/day of estradiol-17beta for 5 (n = 6) or 8 (n = 6) days or with vehicle (n = 8). Nitric oxide synthase mRNA was measured by ribonuclease protection assay, and NOS protein mass was measured by Western immunoblotting. Data were analyzed by ANOVA and Tukey's test. The three distinct uterine compartments studied contained the mRNA and protein for the neuronal (type I NOS) and the endothelial (type III NOS) isoforms of NOS. However, no inducible NOS was detected. Estrogen exhibited a differential effect on NOS expression in a tissue compartment- and NOS isoform-specific manner. In myometrium and caruncles, but not in endometrium, type I NOS mRNA and protein mass increased significantly (p < 0.05) after 5 or 8 days of estrogen. In contrast, type III NOS increased significantly in myometrium only after 8 days, whereas in endometrium and caruncles the increase was significant in the 5-day treatment group (p < 0.05). We conclude that the expression of type I NOS and type III NOS in the uterus are differentially regulated by estrogen. This differential regulation suggests that the NO produced within the uterus serves more than one physiological role. In myometrium it may be a uterorelaxant and regulate glucose utilization, and in endometrium and myometrium it may regulate blood flow.

Uterine relaxation responses to calcitonin gene-related peptide and calcitonin gene-related peptide receptors decreased during labor in rats

OBJECTIVES

Our purpose was to investigate (1) whether uterine relaxation responses to calcitonin gene-related peptide are differentially regulated during pregnancy and labor, (2) the involvement of nitric oxide in smooth muscle relaxant action of calcitonin gene-related peptide in the rat uterus, (3) whether receptors for calcitonin gene-related peptide are expressed in rat uterus, and if so (4) whether the concentrations of these receptors are differently regulated during pregnancy and labor.

STUDY DESIGN

Rats were killed on day 18 of gestation, at the time of spontaneous labor, or postpartum day 2. The uteri were removed for in vitro contractility measurements, nitric oxide production, and calcitonin gene-related peptide receptor binding assay.

RESULTS

(1) Calcitonin gene-related peptide induced a dose-dependent relaxation in spontaneously contracting uterine strips from pregnant rats on day 18 of gestation; (2) the relaxation effects of calcitonin gene-related peptide on the uterus were decreased during spontaneous delivery at term and post partum compared with that during pregnancy; (3) calcitonin gene-related peptide-induced relaxation was inhibited by pretreatment of the uterine tissue with a calcitonin gene-related peptide receptor antagonist, calcitonin gene-related peptide(8-37); (4) nitric oxide synthesis inhibitor (N(G)-nitro-L-arginine methyl ester) and soluble guanylate cyclase inhibitor (LY83583) significantly decreased calcitonin gene-related peptide-induced relaxation of the rat uterus during pregnancy; (5) calcitonin gene-related peptide increased the uterine nitric oxide production in pregnant rats, and this increase was obliterated in the presence of calcitonin gene-related peptide(8-37); and (6) calcitonin gene-related peptide receptors are present in rat uterus, and the concentration of these receptors dramatically increases during pregnancy and decreases during labor at term.

CONCLUSIONS

Calcitonin gene-related peptide inhibits uterine spontaneous contractions in rats during pregnancy but not during labor and post partum. The inhibitory effects of calcitonin gene-related peptide on uterine contractility appear to be modulated, at least in part, by the activation of nitric oxide generation in the rat uterus. Changes in calcitonin gene-related peptide receptors could contribute to the changes in calcitonin gene-related peptide-mediated uterine relaxation during pregnancy and labor.