Modulation of vascular tone by nitric oxide and endothelin 1 in myometrial resistance arteries from pregnant women at term

Dystocic Labor and Adrenergic and Noradrenergic Neurotransmitters: A Morphological Experimental Study

Authors investigated the catecholaminergic neurotransmitters (chNs) quantitative modifications in pregnant uterine Lower Uterine Segment (LUS) during prolonged labor (PL) with the fetus in an occiput-posterior position (OPP), in occiput transverse position (OTP) and in fetal head asynclitism, all diagnosed by Intrapartum Ultrasonography (IU). The chNs neurotransmitters, particularly adrenaline (or epinephrine-A) and noradrenaline (or norepinephrine-N), were evaluated in LUS fragments sampled during CS of 34 patients undergoing urgent cesarean section (CS) in PL, compared to chNs fibers in the LUS of 36 women submitted to elective CS. All results were statistically analyzed to understand the differences in neurotransmitters morphological analysis by scanning electronic microscopy examination (SEM). The LUS fragments analysis revealed a reduction of A and N fibers in LUS during PL, compared with the expression of A and N fibers in LUS during elective CS. The PL for OPP, the OTP and asynclitism, all positions causing dystocia in labor lead to a reduction in neurotransmitters in LUS, with a uterine vascularization modification and a reduction in the contractility of smooth uterine cells. The A and N neurotransmitters reduction observed in PL negatively interferes with uterine contraction during labor.

Uteroplacental Circulation in Normal Pregnancy and Preeclampsia: Functional Adaptation and Maladaptation

Uteroplacental blood flow increases as pregnancy advances. Adequate supply of nutrients and oxygen carried by uteroplacental blood flow is essential for the well-being of the mother and growth/development of the fetus. The uteroplacental hemodynamic change is accomplished primarily through uterine vascular adaptation, involving hormonal regulation of myogenic tone, vasoreactivity, release of vasoactive factors and others, in addition to the remodeling of spiral arteries. In preeclampsia, hormonal and angiogenic imbalance, proinflammatory cytokines and autoantibodies cause dysfunction of both endothelium and vascular smooth muscle cells of the uteroplacental vasculature. Consequently, the vascular dysfunction leads to increased vascular resistance and reduced blood flow in the uteroplacental circulation. In this article, the (mal)adaptation of uteroplacental vascular function in normal pregnancy and preeclampsia and underlying mechanisms are reviewed.

Placental Origins of Preeclampsia: Potential Therapeutic Targets

Preeclampsia (PE) remains a leading cause of maternal and perinatal morbidity and mortality in obstetrics worldwide. No effective treatments to reduce its incidence and severity in clinical practice are currently available. A variety of hypotheses have been generated aiming to explain the origins of PE, notably being the genetic predispositions and placental dysfunction. As regard to placental dysfunction, much progress has been made in basic research and several potential therapeutic targets have been identified. This review will discuss in detail the potential therapeutic targets in PE models including uteroplacental blood flow, oxidative stress, vasoactive factors and inflammation/immune response, and introduce the evolving technologies for placental research nowadays.

Effect of inducible nitric oxide synthase and neuropeptide Y in plasma and placentas from intrahepatic cholestasis of pregnancy

AIM

To analyze inducible nitric oxide synthase (iNOS) and neuropeptide Y (NPY) expression in maternal plasma and placentas of human with intrahepatic cholestasis of pregnancy (ICP).

METHODS

The plasma and placentas were collected from 35 women with normal pregnancies and 33 women with ICP. Enzyme-linked immunosorbent assays were used to investigate maternal plasma iNOS and NPY levels. The mRNA levels and cell-specific localization of iNOS and NPY were determined by quantitative PCR, Western Blotting and immunohistochemical analysis in placentas.

RESULTS

In human placentas, it revealed iNOS and NPY were mainly localized in syncytiotrophoblast, cytotrophoblastin and vascular endothelium cells using immunohistochemistry analysis. iNOS protein and mRNA expression in ICP maternal plasma and placental tissue were significantly lower than in control groups (P <0.01). In maternal plasma and placentas tissue from ICP patients, a marked up-regulation of NPY protein and mRNA expression were observed (P <0.01).

CONCLUSION

iNOS and NPY may play a role in the effect of maternal cholestasis on the placenta. The down-regulation of iNOS and up-regulation of NPY in ICP may influence the blood flow of the utero-placental-fetal unit, which may play a significant role in poor fetoplacental vascular perfusion, acute hypoxia and adverse pregnancy outcomes.

Prophylactic treatment for preeclampsia in high-risk teenage primigravidae with nitric oxide donors: a pilot study

OBJECTIVES

Preeclampsia is associated with significant morbidity and mortality especially in high-risk groups. Impairment of endogenous nitric oxide has been shown to be associated with the disease and prophylactic therapy may ameliorate this condition and improve pregnancy outcome. This study valuated nitric oxide donors prophylactic treatment for preeclampsia in high-risk teenage primigravidae.

METHODS

The study included three hundred primigravidae aged ≤ 20 years with singleton pregnancy. Abdominal pulsed color Doppler ultrasound was done at 24 weeks gestation and pregnancies with uterine artery diastolic notch were randomly allocated to a control group received placebo vaginal tablets and a study group received isosorbid mononitrate 20 mg tablet once daily applied vaginally until delivery.

OUTCOMES

Incidence of preeclampsia and maternal, fetal, and neonatal outcome in both groups.

RESULTS

The study group had significant lower incidence of preeclampsia, preterm birth, intrauterine growth restriction and of neonatal admission to the intensive care (p < 0.05).

CONCLUSIONS

Nitric oxide donors prophylactic treatment for preeclampsia in high-risk teenage pregnancies decrease the incidence of preeclampsia and improve maternal, fetal, and neonatal outcomes. Further studies on larger sample size are required to confirm these results.

Oxytocin, its antagonist Atosiban, and preterm labor: a role for placental nitric oxide

OBJECTIVE

The aim of the present study was to understand the role played by Atosiban, an oxytocin receptor antagonist, on trophoblastic human cells, and the molecular bases of its efficacy and safety in the treatment of preterm labor. NO, peroxinitrite production and NOS expression have been evaluated on placenta obtained from term and preterm labors.

PATIENTS AND METHODS

We studied trophoblast cells isolated from selected placental tissue from 20 controls and 20 preterm patients after cesarean sections. Each sample was studied at basal state and after 2 hours incubation with oxytocin and Atosiban.

RESULTS

Significant variations of NO levels, peroxynitrite production and iNOS and eNOS expression both in the preterm, term samples and in each of the considered groups were observed. In the control group Atosiban re-established NO levels that were reduced after incubation with oxytocin, while in preterm samples NO levels were not only re-established but, after incubation with Atosiban, significantly increased compared to basal levels.

CONCLUSIONS

This confirms the beneficial role of Atosiban in prolonging the pregnancy of spontaneous labor at very early gestational periods. In conclusion, Atosiban might be an effective drug to prevent preterm labor, in the therapeutic approach to this pathology.

Differential vasodilation of human placental and myometrial arteries related to myofilament Ca(2+)-desensitization and the expression of Hsp20 but not MYPT1

Endothelial-dependent regulation of vascular tone occurs in part via protein kinase G1α-mediated changes in smooth muscle myofilament sensitivity to Ca(2+). Tissue-specific differences in PKG-dependent relaxation have been attributed to altered expression of myofilament-associated proteins that are substrates for PKG binding. These include the alternative splicing of the myosin targeting subunit (MYPT1) of myosin light chain phosphatase to yield leucine zipper positive (LZ(+)) and negative (LZ(-)) isovariants, with the former being required for PKG-mediated relaxation, and/or altered expressions of telokin, vasodilator-stimulated phosphoprotein (VASP) or heat shock protein Hsp20. During human pregnancy the uterine and placental circulations remain distinct entities and, as such, their mechanisms of vascular tone regulation may differ. Indeed, the sensitivity of myometrial arteries to endothelial-dependent agonists has been suggested to be greater than that of placental arteries. We tested the hypothesis that this was related to tissue-specific changes in PKG-mediated myofilament Ca(2+)-desensitization and/or the expressions of PKG-interacting myofilament-associated proteins. Permeabilized human placental and myometrial arteries were constricted with maximal activating Ca(2+) (pCa 4.5), or sub-maximal Ca(2+) (pCa 6.7) and the thrombane mimetic U46619, and exposed to 8-Br-cGMP. In each case, relaxation was significantly greater in myometrial arteries (e.g. relaxation in pCa 4.5 to 8-Br-cGMP was 49 ± 9.7%, n = 7) than placental arteries (relaxation of 23 ± 6.6%, n = 6, P < 0.05). MYPT1 protein levels, or MYPT1 LZ(+)/LZ(-) mRNA ratios, were similar for both artery types. Of other proteins examined, only Hsp20 expression was significantly elevated in myometrial arteries than placental arteries. These results demonstrate that the reduced human placental artery relaxation to PKG stimulation lies partly at the level of myofilament (de)activation and may be related to a lower expression of Hsp20 than in myometrial arteries.

Pregnancy increases myometrial artery myogenic tone via NOS- or COX-independent mechanisms

Myogenic tone (MT) is a primary modulator of blood flow in the resistance vasculature of the brain, kidney, skeletal muscle, and perhaps in other high-flow organs such as the pregnant uterus. MT is known to be regulated by endothelium-derived factors, including products of the nitric oxide synthase (NOS) and/or the cyclooxygenase (COX) pathways. We asked whether pregnancy influenced MT in myometrial arteries (MA), and if so, whether such an effect could be attributed to alterations in NOS and/or COX. MA (200-300 μm internal diameter, 2-3 mm length) were isolated from 10 nonpregnant and 12 pregnant women undergoing elective hysterectomy or cesarean section, respectively. In the absence of NOS and/or COX inhibition, pregnancy was associated with increased MT in endothelium-intact MA compared with MA from nonpregnant women (P < 0.01). The increase in MT was not due to increased Ca(2+) entry via voltage-dependent channels since both groups of MA exhibited similar levels of constriction when exposed to 50 mM KCl. NOS inhibition (N(ω)-nitro-L-arginine methyl ester, L-NAME) or combined NOS/COX inhibition (L-NAME/indomethacin) increased MT in MA from pregnant women (P = 0.001 and P = 0.042, respectively) but was without effect in arteries from nonpregnant women. Indomethacin alone was without effect on MT in MA from either nonpregnant or pregnant women. We concluded that MT increases in MA during human pregnancy and that this effect was partially opposed by enhanced NOS activity.

Humans at high altitude: hypoxia and fetal growth

High-altitude studies offer insight into the evolutionary processes and physiological mechanisms affecting the early phases of the human lifespan. Chronic hypoxia slows fetal growth and reduces the pregnancy-associated rise in uterine artery (UA) blood flow. Multigenerational vs. shorter-term high-altitude residents are protected from the altitude-associated reductions in UA flow and fetal growth. Presently unknown is whether this fetal-growth protection is due to the greater delivery or metabolism of oxygen, glucose or other substrates or to other considerations such as mechanical factors protecting fragile fetal villi, the creation of a reserve protecting against ischemia/reperfusion injury, or improved placental O(2) transfer as the result of narrowing the A-V O(2) difference and raising uterine P(v)O₂. Placental growth and development appear to be normal or modified at high altitude in ways likely to benefit diffusion. Much remains to be learned concerning the effects of chronic hypoxia on embryonic development. Further research is required for identifying the fetoplacental and maternal mechanisms responsible for transforming the maternal vasculature and regulating UA blood flow and fetal growth. Genomic as well as epigenetic studies are opening new avenues of investigation that can yield insights into the basic pathways and evolutionary processes involved.

Maternal and fetal circulating sKL and ET-1 levels as function of normal labor at term

OBJECTIVES

To determine whether labor is associated with alterations of the levels of soluble c-kit ligand (sKL) and endothelin-1 (ET-1) in maternal plasma and umbilical cord blood.

METHODS

The sKL and ET-1 levels were investigated in umbilical cord and maternal plasma on the day of delivery in 18 pregnant women with vaginal delivery during labor, 18 non-pregnant women and 9 pregnant women before cesarean delivery, using an ELISA assay.

RESULTS

Umbilical cord plasma sKL levels were significantly higher than the maternal plasma in both types of delivery (p = 0.0001, p < 0.0001, respectively). However, maternal plasma ET-1 levels in the presence of labor were significantly higher than the cesarean delivery group (p < 0.0001). No difference was noted for sKL and ET-1 in umbilical cord vessels of both groups. Furthermore, a highly significant inverse correlation was documented between the individual levels of cord plasma ET-1 and the levels of cord plasma sKL (r = -0.6269, p = 0.0054).

CONCLUSIONS

The sKL levels found in umbilical cord plasma are consistent with the pleiotropic effects of sKL in facilitating the transition of the fetus to the neonatal stage. The reduced ET-1 maternal plasma levels, compared to non-pregnant women, probably are indicative of a putative mechanism for embryo protection from vasoconstriction sequelae. This assumption is strengthened by the corresponding ET-1 levels in umbilical cord plasma.

Effects of pregnancy, hypertension and nitric oxide inhibition on rat uterine artery myogenic reactivity

BACKGROUND/AIMS

The purpose of this study was to examine the effects of hypertension and nitric oxide (NO) inhibition on myogenic tone in uterine arteries during pregnancy.

METHODS

Premyometrial radial uterine arteries from nonpregnant and late pregnant Sprague-Dawley rats were evaluated for myogenic reactivity from the following groups: control, hypertensive/NO-inhibited (L-NAME treatment) and normotensive/NO-inhibited (L-NAME plus hydralazine).

RESULTS

In both nonpregnant and pregnant animals, L-NAME treatment significantly elevated blood pressures, while the addition of hydralazine made the animals normotensive. In nonpregnant animals, little myogenic tone was seen in controls; tone increased significantly in the L-NAME group, and was attenuated in those treated with L-NAME plus hydralazine. In pregnant animals, controls developed significant tone; this was reduced in the L-NAME group, and returned to control levels in the L-NAME plus hydralazine group.

CONCLUSIONS

Dimensional measurements showed that arteries from the pregnant hypertensive group did not undergo expansive remodeling, suggesting that tone development is related to phenotypic alterations in vascular smooth muscle and/or altered physical forces secondary to adaptive changes in arterial diameter. These differences implicate pregnancy-specific pathways in the development and inhibition of myogenic tone, and point to potentially opposing roles of NO and hypertension.

Inhibition of nitric oxide synthases abrogates pregnancy-induced uterine vascular expansive remodeling

BACKGROUND/AIMS

It was the aim of this study to test the hypothesis that hypertension and/or inhibition of nitric oxide (NO) synthases alters uterine vascular remodeling during pregnancy.

METHODS

Using a model of hypertension (NO synthase inhibition with L-NAME) in nonpregnant and pregnant rats, comparisons were made with age-matched controls, as well as with animals receiving hydralazine along with L-NAME to maintain normotension in the presence of NO synthase inhibition. Circumferential and axial remodeling of large (main uterine, MUA) and small (premyometrial radial) arteries were quantified and compared.

RESULTS

L-NAME treatment prevented expansive circumferential remodeling of the MUA; cotreatment with hydralazine was without effect. Circumferential remodeling of smaller premyometrial radial arteries was also significantly attenuated in hypertensive pregnant animals, while premyometrial radial arteries from rats receiving hydralazine with L-NAME were of intermediate diameter. Neither hypertension nor NO synthase inhibition had any effect on the substantial (200-300%) axial growth of MUA or premyometrial radial arteries.

CONCLUSION

NO plays a major role in facilitating pregnancy-induced expansive remodeling in the uterine circulation, particularly in larger arteries. Some beneficial effects of hydralazine on expansive circumferential remodeling were noted in smaller radial vessels, and these may be linked to its prevention of systemic hypertension and/or to local effects on the arterial wall. Neither NO synthase inhibition nor hypertension had any effect on arterial longitudinal growth.

Gender-Specific Alteration of Adrenergic Responses in Small Femoral Arteries From Estrogen Receptor-β Knockout Mice

Estrogen receptor-beta knockout mice become hypertensive as they age, and males have a higher blood pressure than females. We hypothesized that the absence of estrogen receptor-beta may contribute to development of cardiovascular dysfunction by modification of adrenergic responsiveness in the peripheral vasculature. Small femoral arteries (internal diameter <200 microm) were isolated from estrogen receptor-beta knockout and wild-type mice and mounted on a wire myograph. Concentration-response curves to phenylephrine and norepinephrine were compared and the contribution of adrenoceptor subtypes established using specific agonists and antagonists. The involvement of endothelial factors in the modulation of resting tone was also investigated and immunohistochemical analysis used to confirm the presence or absence of estrogen receptor expression. Compared with wild type, arteries from estrogen receptor-beta knockout male, but not female, mice demonstrated gender-specific enhancement of the response to phenylephrine (alpha1-adrenoceptor agonist), which was accompanied by elevated basal tension attributable to endothelial factors. Contractile responses to the mixed adrenoceptor agonist norepinephrine did not differ significantly between estrogen receptor-beta knockout and wild type; however, beta-adrenoceptor inhibition unmasked an enhanced underlying alpha1-adrenoceptor responsiveness in estrogen receptor-beta knockout males. beta-adrenoceptor-mediated dilatation was also enhanced in estrogen receptor-beta knockout versus wild-type males. We suggest that estrogen receptor-beta modifies the adrenergic control of small artery tone in males but not in females.

Contribution of endogenous endothelin-1 to basal vascular tone during normal pregnancy and preeclampsia

OBJECTIVE

The aim of this study was to determine the physiologic role for endogenous endothelin in the regulation of vascular tone during normal pregnancy and preeclampsia. The vascular sensitivity to endothelin-1 during pregnancy was studied also.

STUDY DESIGN

Forearm blood flow was measured by venous occlusion plethysmography during intra-arterial infusion of phosphoramidon, an endothelin-converting enzyme inhibitor, for 60 minutes, which was followed by co-infusion with endothelin-1 for 30 minutes. Three groups were studied: healthy nonpregnant women, normal pregnant women, and women with preeclampsia.

RESULTS

There was a significant increase in forearm blood flow in the nonpregnant group after phosphoramidon infusion alone (73%+/-37%; P<.05). Phosphoramidon did not change forearm blood flow in pregnant subjects. Co-infusion with endothelin-1 significantly decreased forearm blood flow in both the nonpregnant and normal pregnant women (53%+/-7% and 40%+/-11%, respectively; P<.01). No response to endothelin-1 was found among women with preeclampsia.

CONCLUSION

The vascular sensitivity to endothelin-1 is not altered during normal pregnancy in contrast to preeclamptic pregnancy, where no effect of endothelin-1 was seen. Reduced endothelin dependence during pregnancy might be one mechanism behind the fall in peripheral vascular resistance.

Endothelial function in conduit and resistance arteries in men with coronary disease

The aims of this study were to determine whether non-invasive measurement of endothelial function in conduit arteries reflects that of subcutaneous resistance arteries measured in vitro and to examine whether there is an endothelial dysfunction also in resistance arteries in patients with a previous myocardial infarction. The brachial artery diameter responses to a hyperemic flow stimulus and an in vitro method, pressure myography, to directly evaluate flow-mediated responses in arteries obtained from biopsies of subcutaneous fat were measured in 25 patients with a previous myocardial infarction and in 8 aged matched healthy subjects. Flow-mediated dilatation of the brachial artery was more pronounced in the healthy group compared with the group with coronary disease, 5.1 +/- 2.5% and 2.6 +/- 2.1%, respectively (p < 0.05). The flow-mediated dilatation in subcutaneous arteries from CHD patients was significantly reduced compared to control subjects (e.g. percent change from initial preconstriction at maximum flow rate of 204 microl/min: 42 +/- 7% CHD (n = 25) versus 84 +/- 24% control (n = 8), ANOVA, p = 0.03). There was a significant correlation between flow-mediated dilatation of the brachial artery and maximum flow-mediated dilatation at microvascular level, (p < 0.01). In conclusion this study demonstrates endothelial dysfunction in both conduit and resistance circulation in patients after myocardial infarction compared to an aged-matched healthy control group. Furthermore, a significant and independent relationship between endothelial function by means of flow-mediated dilatation in large conduit arteries and resistance arteries was observed.

Effects of blockade of the endothelin receptor A and inhibition of nitric oxide synthesis on uteroplacental and renal blood flow in awake pregnant rats

OBJECTIVE

The aim of this study was to evaluate the role of the ETA receptor and nitric oxide (NO) in the regulation of uteroplacental and renal blood flow in pregnant rats.

STUDY DESIGN

Regional blood flows were measured by the microsphere technique in pregnant Sprague-Dawley rats (term 23 days). Blood flow was measured before and after ETA receptor blockade (BQ-123, 1 mg/kg) at gestational day (GD) 19 or 21 (n=8 and n=9, respectively). In 2 additional groups blood flow was measured before and after NO synthase inhibition (L-NAME 2 microg/min) at GD 19 or 21 (n=10 in each group).

RESULTS

BQ-123 significantly increased placental and myometrial blood flows by almost 80% and 35%, respectively, at both gestational ages. BQ-123 did not alter renal blood flow. No effect on placental or myometrial blood flow was observed after L-NAME infusion, neither at GD 19 nor GD 21. Renal blood flow decreased by nearly 35% in both groups after L-NAME.

CONCLUSION

There is an important role for endogenous ET in the regulation of uteroplacental blood flow in the rat. NO contributes to a significant vasodilatation in the renal vasculature; however, NO appears not to be involved in the maintenance of uteroplacental blood flow in the awake pregnant rat.

Myogenic reactivity is enhanced in rat radial uterine arteries in a model of maternal undernutrition

OBJECTIVES

The purpose of this study was to determine if maternal undernutrition during pregnancy altered myogenic tone in small radial uterine arteries.

STUDY DESIGN

Myogenic tone of radial uterine arteries was studied from late pregnant rats (day 20) that were fed either ad libitum or globally restricted diet (moderately severe dietary restriction) throughout pregnancy.

RESULTS

Myogenic tone was enhanced in the radial uterine arteries from the diet-restricted compared with the ad libitum group. Nitric oxide synthase inhibition enhanced myogenic tone in the arteries from the ad libitum group only. Prostaglandin H synthase inhibition had no effect on myogenic tone in either group.

CONCLUSION

Diet restriction during pregnancy enhances myogenic tone in the radial uterine arteries partly as a result of impairment of the nitric oxide synthase pathway. Enhanced myogenic tone in turn may reduce uteroplacental blood flow and, thus, contribute to reduced birth weight, and lead to effects of fetal programming in utero that can have long-term consequences into adulthood.

Chronic hypoxia opposes pregnancy-induced increase in uterine artery vasodilator response to flow

We tested the hypotheses that pregnancy increases the uterine artery (UA) vasodilator response to flow and that this increase is impaired under conditions of chronic hypoxia (30 days, simulated elevation 3,960 m). UA were isolated from 24 normoxic or chronically hypoxic midpregnant guinea pigs and studied with the use of pressure myography. Normoxic pregnancy increased UA flow vasodilator response and protected against a rise in wall shear stress (WSS). Chronic hypoxia opposed these effects, prompting vasoconstriction at high flow and increasing WSS above levels seen in normoxic pregnant UA. The nitric oxide synthase inhibitor N(G)-nitro-l-arginine (l-NNA) eliminated the pregnancy-associated increase in flow vasodilation in normoxic UA, suggesting that increased nitric oxide production was responsible. The considerable residual vasodilation after nitric oxide synthase and cyclooxygenase inhibition implicated endothelial-derived hyperpolarizing factor (EDHF) as an additional contributor to flow vasodilation. l-NNA increased flow vasodilation in UA from chronically hypoxic animals, suggesting that chronic hypoxia may have lowered EDHF or elevated peroxynitrite production. In conclusion, flow is an important physiological vasodilator for the acute and more chronic UA dimensional changes required to increase uteroplacental blood flow during normal pregnancy. Chronic hypoxia may be a mechanism that opposes the pregnancy-associated rise in UA flow vasodilation, thereby increasing the incidence of preeclampsia and intrauterine growth restriction at a high altitude.

Vascular endothelial growth factor induced functional and morphologic signs of endothelial dysfunction in isolated arteries from normal pregnant women

OBJECTIVE

The purpose of this study was to determine the effects of vascular endothelial growth factor on basal tone, endothelium-dependent dilatation, permeability, and morphologic features of endothelium in isolated arteries from normal pregnant women. We hypothesized that vascular endothelial growth factor might induce signs of endothelial dysfunction.

STUDY DESIGN

Arteries (approximately 200 microm) were dissected from subcutaneous fat biopsy specimens that were obtained at cesarean delivery and mounted on a pressure arteriograph. Changes in basal tone, dilatation to bradykinin (1 nmol/L to 3 micromol/L) before, during, and after 3 hours of incubation with vascular endothelial growth factor (0.5 or 1 nmol/L), vascular endothelial growth factor (0.5 nmol/L) plus bosentan (a nonselective endothelin receptor A and B antagonist, 1 micromol/L), or vehicle were compared. Scanning electron microscopy was applied for endothelial morphologic features. Permeability to Evans blue dye was evaluated in arteries after incubation with vascular endothelial growth factor, vascular endothelial growth factor plus angiopoietin-1, or vehicle, and in arteries that were obtained from women with preeclampsia.

RESULTS

Basal tone was higher after 60 minutes of incubation with vascular endothelial growth factor (0.5 nmol/L) compared with vehicle (29% +/- 5% [n = 10] vs 10% +/- 4% [n = 7], P =.006). Combination of vascular endothelial growth factor with bosentan failed to increase the tone (n = 4). Bradykinin-mediated dilatation was impaired in arteries that were incubated with vascular endothelial growth factor 0.5 nmol/L (max dilatation: 287% +/- 16% vs 160% +/- 23% [n = 10], P =.0001) or vascular endothelial growth factor 1 nmol/L (max dilatation: 207% +/- 21% vs 88% +/- 4% [n = 3], P =.003). Bradykinin-mediated dilatation was similar after incubation with vehicle (n = 7) or the combination of vascular endothelial growth factor plus bosentan (n = 4). Evans blue dye staining was higher after incubation with vascular endothelial growth factor but was reversed by the addition of angiopoietin-1. Scanning electron microscopy demonstrated the development of intercellular gaps.

CONCLUSION

Vascular endothelial growth factor impaired bradykinin-mediated dilatation and enhanced basal tone and permeability. This might indicate a potential role for vascular endothelial growth factor in the development of endothelial dysfunction in pregnancy. Angiopoietin-1 inhibited the vascular endothelial growth factor-induced vascular leakage, which may have therapeutic implications in preeclampsia.

Antenatal administration of celecoxib, a selective cyclooxygenase (COX)-2 inhibitor, appears to improve placental perfusion in the pregnant rabbit

To investigate the effects of celecoxib on fetal growth, and placental prostanoid and nitric oxide (NO) production in fetal rabbits, pregnant rabbits received celecoxib (30 mg/kg per day) from 13 to 20 days (Cel-A), from 13 to 28 days (Cel-B), or vehicle from 13 to 28 days gestation. Fetal body and organ weights, and measurements of linear growth were recorded. The placentas were weighed and analyzed for prostaglandins (PGs), NO oxidation products (NOx), and total cellular protein levels. Placental prostaglandin E2 (PGE2) and NOx levels increased (P < or = 0.05), while thromboxane B2 levels were suppressed (P < or = 0.01) in Cel-B group. Tail length and brain weight were greater, while lung weights were lower in the Cel-B group (P < or = 0.05). Maternal administration of celecoxib appears to preferentially increase placental vasodilators and decrease placental TxA2, suggesting that the drug may increase uteroplacental perfusion without adverse fetal outcome.

Vascular adaptations to pregnancy in mice: effects on myogenic tone

The mechanisms underlying vascular adaptations in pregnancy remain to be fully elucidated. One of the contributory mechanisms for reduced vascular tone may be a reduction of myogenic tone. Myogenic tone was assessed as the difference between internal diameter in the presence and absence of external calcium at different intramural pressure steps (60-100 mmHg). Myogenic responses were reduced in resistance-sized mesenteric and main uterine arteries in late pregnant compared with nonpregnant C57BL/6J mice. In vessels from pregnant, but not nonpregnant mice, the myogenic response was enhanced by preincubation with nitric oxide (NO) synthase inhibitor N(G)-nitro-l-arginine methyl ester, was further elevated by the gap junction inhibitor 18-alpha glycyrrhetinic acid, but was unaltered by the prostaglandin H synthase inhibitor meclofenamate. Endothelium removal enhanced myogenic tone only in the vessels from pregnant animals, thus confirming the role of the endothelium in modulating myogenic tone in pregnancy. These results suggest that endothelium-derived NO as well as gap junction communications modulate myogenic tone in mouse pregnancy.

Coronary artery myogenic response in a genetic model of hypertrophic cardiomyopathy

Hypertrophic cardiac myopathy (HCM) is the leading cause of mortality in young athletes. Abnormalities in small intramural coronary arteries have been observed at autopsy in such subjects. The walls of these intramural vessels, especially in the ventricular septum, are thickened, and the lumen frequently appears narrowed. Whether these morphological characteristics have functional correlates is unknown. We studied coronary myogenic tone in a transgenic mouse model of HCM that has mutations in the cardiac alpha-myosin heavy chain gene. This transgenic mouse has a cardiac phenotype that resembles that occurring in humans. We examined the possible vascular contributions to the pathology of HCM. Septal arteries from 3- and 11-mo-old wild-type (WT) and transgenic (TG) mice were studied on a pressure myograph. The myogenic response to increased intravascular pressure in older animals was significantly reduced [maximal constriction: 32 +/- 4% (TG) and 46 +/- 4% (WT), P < 0.05]. After inhibition of endothelin receptors with bosentan, both WT and TG mice had similar increases in myogenic constriction. The sensitivity to exogenous endothelin was significantly reduced in TG mice, suggesting that the reduced myogenic constriction in HCM was due to reduced receptor sensitivity. In conclusion, we show for the first time that 1) myogenic tone in the coronary septal artery of the mouse is regulated by a basal release of endothelin, and 2) pressure-induced myogenic activation is attenuated in HCM, possibly consequent to a reduction in endothelin responsiveness. The associated reduction in coronary vasodilatory reserve may increase susceptibility to ischemia and arrhythmias.

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.

Preeclampsia: evidence for impaired shear stress-mediated nitric oxide release in uterine circulation

OBJECTIVE

We sought to compare flow-mediated dilatation and myogenic and norepinephrine-induced tone in myometrial resistance arteries from women with preeclampsia and healthy pregnant women and to evaluate the role that nitric oxide may play in these responses.

STUDY DESIGN

Arteries (approximately 200 microm, at 50 mm Hg) were dissected from myometrial biopsy specimens from women undergoing emergency cesarean delivery because of preeclampsia (n = 6) and from healthy control subjects undergoing planned cesarean delivery (n = 9). Responses to intraluminal flow, pressure, and a constrictor agonist (norepinephrine, 10(-6) mol/L) were studied in the absence and presence of the nitric oxide synthase inhibitor N omeganitro-L -arginine (10(-4) mol/L). Myogenic and norepinephrine-induced tone were calculated after the determination of artery diameter in the absence of extracellular calcium and in the presence of papaverine (10(-4) mol/L).

RESULTS

An increase in intraluminal flow led to dilatation of isolated myometrial arteries from healthy gravid women, whereas flow-mediated dilatation was absent in arteries from gravid patients with preeclampsia (increase in diameter at maximum flow rate of 204 microL/min, 28% +/- 5% in healthy gravid patients vs -15% +/- 6% in gravid women with preeclampsia; analysis of variance, P <.05). Addition of N omega-nitro-L -arginine had no significant effect on flow-mediated responses in arteries from women with preeclampsia, whereas flow-mediated dilatation was abolished after addition of N omega-nitro-L -arginine in arteries from healthy gravid women (increase in diameter at a maximum flow rate of 204 microL/min, 28% +/- 5% control vs -9% +/- 5% N omega-nitro-L -arginine; analysis of variance, P <.05). Arteries from women with preeclampsia developed pressure-induced myogenic and norepinephrine-induced tone, similar to that obtained in arteries from healthy gravid women. In arteries from gravid women with preeclampsia, inhibition of nitric oxide synthase enhanced myogenic-induced tone (25% +/- 4% control vs 35% +/- 5% N omega-nitro-L -arginine; P <.05) and norepinephrine-induced tone (36% +/- 4% control vs 46% +/- 6% N omega-nitro-L -arginine; P <.05), as in arteries from healthy gravid women.

CONCLUSIONS

Nitric oxide may participate in modulation of pressure- and norepinephrine-induced tone even in preeclampsia, but the shear stress-mediated release of nitric oxide is absent. Failure of shear stress-mediated dilation in myometrial arteries from gravid women with preeclampsia might contribute to the impaired uteroplacental blood flow in this disease.