Estrogen does not induce the calcium-dependent nitric oxide synthase in cultured human uterine endothelial and myometrial smooth muscle cells

Expression of endothelial nitric oxide synthase in the uterus of patients with leiomyoma or adenomyosis

AIM

To confirm the difference in the expression of endothelial nitric oxide synthase in the normal endometrium and myometrium of women who have leiomyoma or adenomyosis compared with controls, and its correlation with the pathogenesis of menorrhagia or dysmenorrhea in patients with uterine leiomyoma.

METHODS

Fifty-one hysterectomized patients were divided into three groups: (i) patients with leiomyoma (n=24); (ii) those with adenomyosis (n = 19); and (iii) the control group (n=8). The expression of endothelial nitric oxide synthase was confirmed on immunohistochemistry and analyzed using an evaluation nomogram.

RESULTS

The expression of endothelial nitric oxide synthase was significantly higher in the leiomyoma group and the adenomyosis group as compared with the control group. In the subgroup analysis of leiomyoma depending on symptoms (menorrhagia or dysmenorrhea or both), the expression of endothelial nitric oxide synthase was significantly higher in the symptomatic subgroup than the asymptomatic subgroup (endometrium P=0.0029, myometrium P=0.0276).

CONCLUSIONS

Based on the findings that the expression of endothelial nitric oxide synthase was significantly higher in the uterus with leiomyoma or adenomyosis, it can therefore be inferred that nitric oxide might have a pathological effect on the uterus with the above diseases. In particular, it is also presumed that endothelial nitric oxide synthase is closely associated with menorrhagia and dysmenorrhea.

Regulation of nitric oxide synthase isoforms by estrogen in the human endometrium

OBJECTIVE

To examine the influence of estrogen on the expression of nitric oxide synthase (NOS) isoforms in human endometrial surface epithelial cell line (HES) and primary endometrial cells.

DESIGN

Laboratory-based investigation.

SETTING

Academic center.

INTERVENTION(S)

The expression of NOS isoform protein levels and mRNA was determined following estrogen/progesterone stimulation.

MAIN OUTCOME MEASURE(S)

NOS protein and mRNA levels in HES and primary endometrial cells.

RESULT(S)

Estradiol 17-beta (E2) induced a dose- and time-dependent increase in the expression of eNOS mRNA and protein and iNOS protein in HES cells which could be blocked by the estrogen receptor antagonist ICI 182,780. Estradiol increased the expression of eNOS mRNA and protein in primary endometrial cells. Estrogen also induced phosphorylation of eNOS which could not be blocked by ICI 182,780. Progesterone in physiologic concentrations augmented the effect of estrogen on the expression of both eNOS and peNOS but not of iNOS. ICI 182,780 in high concentrations stimulated the expression of iNOS protein while inhibiting eNOS.

CONCLUSION(S)

Estradiol through a genomic mechanism stimulates the expression of NOS isoforms in endometrial derived primary and HES cells. This effect is potentiated by progesterone.

Estrogen modulation of endothelium-derived relaxing factors by human endothelial cells

We report the modulatory effects of estrogen on release of endothelium-derived relaxing factors (EDRFs) in a human endothelial cell line, EA.hy926. Using bioassay, we showed that EA.hy926 released EDRF including nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) measured by relaxation of pre-contracted endothelium-denuded rabbit aortic rings. This EDRF production was significantly higher in cells treated for 24 h with 17-beta-estradiol (10(-6)mol/L) than control cells. Addition of L-NAME to the perfusate of cells caused the relaxation induced by the endothelial cell perfusate to become transient and abolished the enhancement of relaxation due to estrogen treatment. Addition of K(Ca) channel blockers to the perfusate abolished the L-NAME-resistant relaxation of the bioassay ring. Using real-time PCR, we demonstrated that eNOS expression in estrogen-treated cells was significantly higher than controls. These results show that estrogen exerts a potentially important vasculo-protective effect by stimulating NO but not EDHF production.

NAB2, a corepressor of EGR-1, inhibits vascular endothelial growth factor-mediated gene induction and angiogenic responses of endothelial cells

In this study we have investigated the role of a specific corepressor of EGR-1, NAB2, to down-regulate vascular endothelial growth factor (VEGF)-induced gene expression in endothelial cells and to inhibit angiogenesis. Firstly, we show a reciprocal regulation of EGR-1 and NAB2 following VEGF treatment. During the initial phase EGR-1 is rapidly induced and NAB2 levels are down-regulated. This is followed by a reduction of EGR-1 and a concomitant increase of NAB2. Secondly, using the tissue factor gene as a readout for VEGF-induced and EGR-1-regulated gene expression we demonstrate that NAB2 can completely block VEGF-induced tissue factor reporter gene activity. Thirdly, by adenovirus-mediated expression we show that NAB2 inhibits up-regulation of tissue factor, VEGF receptor-1, and urokinase plasminogen activator mRNAs even when a combination of VEGF and bFGF is used for induction. In addition, NAB2 overexpression significantly reduced tubule and sprout formation in two different in vitro angiogenesis assays and largely prevented the invasion of cells and formation of vessel-like structures in the murine Matrigel model. These data suggest that NAB2 regulation represents a mechanism to guarantee transient EGR-1 activity following exposure of endothelial cells to VEGF and that NAB2 overexpression could be used to inhibit signals involved in the early phase of angiogenesis.

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.

Chronic and acute effects of oestrogens on vascular contractility

In addition to their role as sex hormones, it has been known for many years that oestrogens have protective effects on the vasculature. These have been implicated in the reduced incidence of cardiovascular disorders in premenopausal women and in post-menopausal women receiving oestrogen replacement therapy. This protection has been found to be due, in part at least, to direct effects of oestrogens on blood vessels. This review will summarize the available literature regarding oestrogenic effects on vascular contractility. Two major influences of oestrogens will be discussed; first the genomic effects induced by chronic administration of steroid hormones, and second, the rapid effects on vascular smooth muscle by non-genomic, and as yet not fully identified, mechanisms. In so doing, the diversity of oestrogenic actions on vascular contractility will be highlighted and the protective role of these agents against adverse cardiovascular events discussed.

Decreasing estrogen in nonpregnant women lowers uterine myometrial type I nitric oxide synthase protein expression

OBJECTIVE

Our purpose was to study the effect of estrogen on myometrial nitric oxide synthase.

STUDY DESIGN

Twenty-four women were randomly assigned to treatment with gonadotropin-releasing hormone agonist or placebo for 8 weeks before hysterectomy, at which time samples of myometrium were collected and the serum levels of estrogen, nitrate, and nitrite measured. Myometrial nitric oxide synthase was measured with the arginine-citrulline assay. The levels of endothelial nitric oxide synthase and neuronal nitric oxide synthase were determined by Western blot analysis.

RESULTS

Myometrial nitric oxide synthase was 88% calcium dependent but only partially calmodulin dependent. Women treated with gonadotropin-releasing hormone agonist had postmenopausal levels of estradiol and had significantly lower levels of myometrial neuronal nitric oxide synthase than those in the control group. Total, endothelial, and inducible nitric oxide synthase levels in the myometrium were unchanged, as were serum nitrite and nitrate levels.

CONCLUSION

Neuronal nitric oxide synthase is regulated in the myometrium by estrogen. Myometrial nitric oxide synthase is not all calmodulin dependent; this may represent the activity of a novel nitric oxide synthase isoform.

Human cervical ripening is associated with an increase in cervical inducible nitric oxide synthase expression

The mechanisms that ultimately regulate cervical ripening during parturition remain largely unknown. A possible role for nitric oxide (NO) has recently emerged; however, the expression of NO synthase (NOS) within the human cervix in the ripening process has not been investigated. The purpose of this study was to identify cell types in the human cervix that contain NOS isoforms and to examine changes in their expression during the ripening process and the nonpregnant state. Inducible NOS (iNOS) immunoreactivity was observed in the epithelial cells and stromal spindle cells in 17 of 20 biopsies from cervices obtained within 10 min postpartum, but in only 4 of 12 nonpregnant controls (p = 0.03). Endothelial NOS (eNOS) immunoreactivity was restricted to vascular endothelia in all sections, whereas neuronal NOS was not detectable. Inducible NOS activity in the postpartum group was 3.2 times that of the control group (p = 0.0005), whereas constitutive NOS activity remained unchanged in both groups (p = 0.222). Competitive reverse transcription-polymerase chain reaction revealed no differences in the expression of iNOS (p = 0.443) or eNOS mRNA (p = 0.409). The existence of iNOS in the human postpartum cervix suggests that increased production of NO, probably induced by cytokines, may be relevant to the process of natural cervical ripening in humans.

Gender differences in coronary artery diameter reflect changes in both endothelial Ca2+ and ecNOS activity

Elevation of nitric oxide (NO) release from the vascular endothelium may contribute to some of the gender-associated differences in coronary artery function. The mechanisms by which gender affects NO release from the endothelium of coronary arteries are not known. In this study, endothelial function was examined in pressurized coronary arteries from female and male rats. Diameter and endothelial cell intracellular Ca2+ concentration ([Ca2+]i) in intact arteries, as well as enzymatic activity of endothelial constitutive nitric oxide synthase (ecNOS) in arterial lysates, was measured. Elevation of intravascular pressure to 60 mmHg constricted coronary arteries from female animals less than coronary arteries from male animals (18% and 31% constriction, respectively). The increased arterial diameter of coronary arteries from females was associated with elevated endothelial [Ca2+]i (female 174 nM, male 90 nM; P < 0.001). Elevation of Ca2+ activated ecNOS with a similar slope and half-activation constant ( approximately 160 nM) for both female and male coronary arteries. However, at [Ca2+] > 100 nM, ecNOS activity was significantly higher in coronary arteries from female rats compared with their male equivalents (P < 0.01). Maximal activity for ecNOS at saturating Ca2+ (300 nM) was 37% higher in coronary arteries from female animals compared with male animals (P < 0.05). Thus elevated [Ca2+]i in the endothelium of female coronary arteries alone is predicted to increase the production of NO (by nearly 2-fold). This gender difference combined with increased ecNOS activity at a given [Ca2+] in females indicates that tonic NO production should be nearly threefold greater in female coronary arteries compared with male coronary arteries. We conclude that, in the regulation of endothelial Ca2+ and ecNOS, gender differences contribute significantly to the overall decrease in myogenic tone observed in coronary arteries of females.

Elevation of inducible nitric oxide synthase activity in human endometrium during menstruation

Nitric oxide (NO) is a known agonist of programmed cell death (apoptosis). In order to discover its potential role during menstrual shedding, a process associated with extensive apoptosis, we evaluated activity and mRNA levels of the inducible and constitutive isoforms of NO synthase (NOS) in endometrial specimens of the proliferative (n = 11), late-secretory (n = 7), and menstrual (n = 17) phase of the cycle. These levels were compared with the proportion of apoptotic cells by detection of histochemically labeled DNA fragments. Inducible NOS (iNOS) activity during menstruation was six times that of the proliferative or late-secretory phase (p < 0.05), whereas constitutive NOS activity remained unchanged. Competitive reverse transcription-polymerase chain reaction revealed 146% and 77% increases of iNOS mRNA expression in the late-secretory and menstrual phases, respectively, compared to the proliferative phase (p < 0.05), whereas constitutive NOS mRNA expression remained constant. Inducible NOS immunostaining was restricted to epithelial cells, whereas constitutive NOS immunostainig was confined to vascular endothelia. In addition, the proportion of apoptotic cells within the glands of late-secretory or menstrual endometrium was twice that of the proliferative phase (p < 0.05). We conclude that local production of NO is involved in the signal transduction mechanisms leading to endometrial breakdown during menstruation.

Endothelial vasodilator production by uterine and systemic arteries. III. Ovarian and estrogen effects on NO synthase

During the follicular phase of the ovarian cycle, when the local estrogen-to-progesterone ratio is elevated, uterine blood flow is elevated. This vasodilatory response is reproduced by exogenous 17beta-estradiol (E2beta) administration via a nitric oxide (NO)-mediated mechanism. We hypothesized that endogenous ovarian estrogen and exogenous E2beta treatment elevate expression of endothelial cell-derived NO synthase (eNOS) in uterine, but not in systemic, arteries. Uterine, mammary, and systemic (renal and/or omental) arteries were collected from 1) ewes synchronized to the follicular (day -1 to day 0) or luteal (day 10) phases of the ovarian cycle (n = 4 per phase), 2) ovariectomized ewes 120 min after systemic vehicle or E2beta (5 micrograms/kg iv) treatment, and 3) ovariectomized ewes on days 0, 3, 6, 8, and 10 of E2beta (5 micrograms/kg iv, followed by 6 micrograms/kg per day) treatment. Expression of eNOS was localized primarily to the endothelium rather than vascular smooth muscle (VSM) in all arteries examined by immunohistochemistry and Western analysis; inducible NOS was not detected in either endothelium or VSM. Expression of eNOS protein was greater (P < 0.05) in uterine, but not in systemic, artery endothelium-isolated protein collected from follicular versus luteal phase ewes. Acute systemic E2beta treatment of ovariectomized ewes increased (P < 0.05) eNOS protein levels in uterine artery endothelium. Prolonged E2beta administration progressively increased uterine, but not systemic, artery endothelial eNOS protein expression. Therefore, the increased local estrogen-to-progesterone ratio during the follicular phase locally elevates eNOS expression, which possibly elevates uterine blood flow. These responses can be partly reproduced with E2beta administration.

Expression of endothelial (type III) nitric oxide synthase in cytotrophoblastic cell lines: regulation by hypoxia and inflammatory cytokines

Expression of endothelial nitric oxide synthase (eNOS) has been localized to the villous syncytiotrophoblasts suggesting that NO release from these cells could prevent platelet adhesion and aggregation in the intervillous space. Hypoxia- or inflammation-dependent changes in the release of this vasoactive substance may result in thrombus formation and altered vascular resistance which occur in the placental bed of pre-eclamptic patients. To evaluate the influence of low-oxygen tension and inflammation on eNOS production in the trophoblast steady-state eNOS mRNA and protein levels were investigated in cytotrophoblastic BeWo and Jeg-3 cells cultured at 3.5 per cent oxygen and/or in the presence of the pro-inflammatory cytokines IL-1 and TNF-alpha. By RT-PCR and immunocytochemistry we demonstrate that BeWo cells produce eNOS mRNA and protein while eNOS polypeptide was undetectable in JEG-3 cells. In BeWo cells addition of both cytokines decreases eNOS mRNA and protein abundancies within 24 h of incubation while each substance alone had no effect. Compared to controls, the amount of eNOS transcripts was found to be elevated at low-oxygen tension, however, cNOS protein was downregulated after 24 h in the hypoxic environment, as shown by immunocytochemistry and Western blot analysis. Forskolin and methotrexate, which induce biochemical differentiation/ growth arrest in choriocarcinoma cells, stimulate eNOS mRNA and protein synthesis, but cannot overcome the decline of eNOS polypeptide levels during hypoxic incubation. It is speculated that acute hypoxia and inflammation impair eNOS/NO production of the trophoblast in vivo, which might contribute to pathological conditions of gestational diseases.

The effect of hormone replacement therapy on carotid arteries: measurement with a high frequency ultrasound system

OBJECTIVE

To evaluate the effect of hormone replacement therapy (HRT) on carotid arteries in postmenopausal women with a high frequency ultrasound system.

METHODS

In a clinical cross-sectional study carotid artery layers were measured in 82 postmenopausal women receiving a sequential regimen of HRT (oestradiol valerate 2 mg and dydrogesterone 10 mg) and in 70 postmenopausal women without HRT. Measurements of the left carotid artery layers (externa, media, intima) were taken with a single mechanically activated 22.5-MHz transducer with an effective band width of 8 MHz.

RESULTS

A statistically significant increase in thickness of the media layer of the carotid artery was observed in the HRT group (0.34 +/- 0.06 mm) as compared to the untreated group (0.27 +/- 0.03 mm). The media/intima ratio of the treated group was statistically significantly higher than that of the untreated group (P < 0.05). The mean strength of the carotid wall was 0.70 +/- 0.17 mm in the 70 postmenopausal women without HRT and 0.76 +/- 0.24 mm in the 82 patients undergoing HRT.

CONCLUSION

HRT has a morphological effect on the carotid arteries in postmenopausal women. These findings support a cardioprotective effect, especially in terms of prevention of atherosclerosis. This effect can be measured non-invasively by high frequency ultrasound.