Lethal progression of a fetal intracranial arteriovenous malformation

Fetal intracranial vascular tumors present unique clinical challenges. Accurate diagnosis of the lesion, as well as an understanding of the local and systemic impacts, will guide the antenatal surveillance and the treatment plan and will determine the prognosis. Management will be altered by and dependent on intrauterine progression, gestational age, and fetal condition at birth. In addition, large vascular tumors can lead to the development of the Kasabach-Merritt sequence in the fetus and to either fetal or maternal hemodynamic impairment. Vascular tumors are either malformations or neoplasms. Color and pulsed wave Doppler sonography are useful for the identification of vascular lesions and help narrow the differential diagnosis. Once a vascular malformation is identified, a comprehensive anatomic survey is mandatory to determine whether there are coexistent malformations that impact either the diagnosis or prognosis. These lesions can have local mass effects, systemic hemodynamic effects, or both. Therefore, longitudinal assessment of the fetus is focused on the detection of lesion progression and on any fetal or maternal status changes. We report the prenatal diagnosis of an intracranial arteriovenous malformation (AVM) with a dramatic progression affecting both mother and fetus.

Uterine contractility in women whose fetus is delivered in the occipitoposterior position

OBJECTIVE

Most fetuses in the occipitoposterior position rotate spontaneously after striking the pelvic floor. The increased prevalence of prolonged labor, operative delivery, and oxytocin augmentation in women with an occipitoposterior fetal position seems consistent with decreased uterine contractility. We sought to test the hypothesis that women with a persistent occipitoposterior fetal position have inadequate intrauterine pressure.

STUDY DESIGN

Intrauterine pressure was measured prospectively electronically in 94 women whose labor pain was controlled by patient-requested epidural analgesia. Eleven women (12%) were delivered as a persistent occipitoposterior fetal position. In a nested case-control study, these women were compared with 22 women who were delivered as an occipitoanterior fetal position who were matched for age, parity, gestational age, cervical examination at study enrollment, and body mass index. The intrauterine pressure measurements were initiated during the first stage of labor and continued throughout the entire labor process. Women were encouraged in the second stage of labor, after a period of recording baseline contractility, to push using a standardized Valsalva maneuver once the vertex reached the +2 station. The area under the intrauterine pressure curve (integral) was used to estimate uterine contractility and expulsive performances.

RESULTS

Five women (45%) in the occipitoposterior group required operative delivery. The average duration of the second stage of labor in the occipitoposterior group was 91.4 +/- 23.2 minutes compared with 51.7 +/- 6.6 minutes in the occipitoanterior fetal position (P =.04). Ninety percent of women in the occipitoposterior group required oxytocin, compared with 59% of the women in the occipitoanterior group (P =.11). There were no differences in uterine contractility between occipitoposterior and occipitoanterior groups during either the first stage of labor (integral mean +/- SEM: occipitoposterior [1685.3 +/- 194.6 mm Hg. s] vs occipitoanterior fetal position [1700.8 +/- 128.9 mm Hg. s, P =.98]) or second stages of labor (occipitoposterior [1952.6 +/- 186.5 mm Hg. s] vs occipitoanterior fetal position [1740.8 +/- 104.3 mm Hg. s, P =.46]). Further, there were no significant differences in pushing performances between the occipitoposterior and occipitoanterior groups (Valsalva maneuver: occipitoposterior 2864.9 +/- 328.8 mm Hg. s] vs occipitoanterior [2898.6 +/- 222.2 mm Hg. s, P =.90]).

CONCLUSION

Women who were delivered as a persistent occipitoposterior fetal position do not have lower intrauterine pressure levels immediately before or during the second stage of labor.

Myometrial thickness during human labor and immediately post partum

OBJECTIVE

Morphologic studies suggest dramatic, asymmetric uterine growth during pregnancy that is caused by muscle cell hypertrophy. This growth is most marked at the fundus. Our objective was to evaluate sonographically the in vivo changes in myometrial thickness during active labor, second-stage labor, and after delivery.

STUDY DESIGN

Abdominal ultrasound scans were performed on 52 term pregnant women to investigate the dynamic changes in myometrial thickness during the active and second stages of labor and immediately after delivery. Twenty-six women (mean +/- SEM gestational age, 39.09 +/- 0.3 weeks) were in active labor (cervical dilatation >4 cm with regular uterine contractions). An additional 26 nonlaboring women (gestational age, 39.8 +/- 0.2 weeks) provided control measurements. The myometrium was defined sonographically as the echo homogeneous layer between the serosa and the decidua. Myometrial thickness was measured at the low segment and mid anterior, fundal, and posterior uterine walls by the same observer. Myometrial thickness was also measured during uterine contractions and after artificial rupture of the amniotic membranes. All laboring women had uncomplicated labor patterns when studied and were delivered spontaneously.

RESULTS

The myometrium was significantly thinner during active labor compared with nonlabor at each site studied: midanterior (mean [+/-SEM] myometrial thickness, 5.8 +/- 0.27 vs 8.83 +/- 0.51 mm; t test, P <.001), fundus (mean myometrial thickness, 6.78 +/- 0.32 vs 8.49 +/- 0.35 mm; P =.0015), and posterior (mean myometrial thickness, 6.22 +/- 0.34 vs 8.12 +/- 0.30 mm; P <.001). However, myometrial thickness did not differ among sites within the two groups. The thickness of the low segment was not affected by labor status (nonlabor, 4.68 +/- 0.48 vs labor, 4.66 +/- 0.37 mm; P =.97). Similarly, the myometrial thickness of the anterior uterine wall was unaffected by contractions (no contractions, 5.56 +/- 0.2 vs contractions, 5.68 +/- 0.22 mm; t test, P =.654). There was no change in myometrial thickness measured immediately before and after rupture of the amniotic membranes, despite a significant decrease of the amniotic fluid index. There was significant thickening of the anterior and fundal myometrium during the second stage of labor after the fetal head descended to +3 station by digital examination (anterior, 12.99 +/- 0.60 vs 5.8 +/- 0.27 mm; t test, P <.001; fundus, 10.61 +/- 1.63 vs 6.78 +/- 0.32 mm; t test, P =.04). Valsalva maneuver (pushing) during contractions did not affect myometrial thickness at the fundus (between contractions, 10.61 +/- 1.63 vs pushing, 10.76 +/- 1.95 mm; t test, P =.99). Immediately after delivery, the myometrial thickness at the placental insertion site was the thinnest. After completion of the third stage of labor, the uterine fundus remained significantly thinner than the anterior and posterior walls (fundus, 27.37 +/- 3.5 mm vs anterior, 40.94 +/- 3.5 vs posterior, 42.34 +/- 2.44; one-way analysis of variance, P =.02).

CONCLUSION

There is significant and widespread thinning of the myometrium during active labor. Descent of the fetal head during the second stage of labor is associated with a significant relative thickening of the anterior and fundal myometrium. After delivery, the relationship reverses. These findings suggest the directionality of the expulsive force vectors (fundal dominance) is not determined by asymmetric myometrial growth but, rather, may be a function of increased "myometrial mass" that results from increased surface area at the fundus.

Protective effect of N-acetylcysteine against fetal death and preterm labor induced by maternal inflammation

OBJECTIVE

Intrauterine and maternal systemic infections are proposed causes of preterm labor. The resulting prematurity is associated with 75% of infant mortality and 50% of long-term neurologic handicaps. We hypothesize that free radicals generated in large quantities during an inflammatory response shift the fetomaternal redox balance to an oxidative state, compromising the fetus. Thus, if our working hypothesis is correct, selective inactivation of free radicals with N-acetylcysteine (NAC), an antioxidant and glutathione (GSH) precursor, would improve the outcome of preterm deliveries associated with inflammation. We tested aspects of this hypothesis in an animal model of preterm labor and fetal damage (death).

STUDY DESIGN

NAC (1 g/kg) was administered orally to C57Bl/6 mice injected intraperitoneally with either 10 microg lipopolysaccharide (LPS) or saline solution (CRL) on day 16 of gestation. The latency period (time from injection to delivery of the first pup) and fetal viability were recorded. To discriminate between an effect of prematurity from an effect of inflammation, and to document any improvement in survival, mice were killed at 3, 6, and 16 hours after injection. Maternal and fetal redox states were approximated by measuring hepatic GSH.

RESULTS

Each C57Bl/6 LPS-treated mouse delivered prematurely after a significantly shorter latency period (LPS: 16.8 hours [95% CI 15.9-17.6] vs CRL: 54.7 hours [95% CI 43.8-65.5]). NAC doubled the latency interval of LPS-treated animals to 35.2 hours (95% CI 21.0-49.2). LPS alone resulted in a 100% rate of stillbirth. Fifty-eight percent of fetuses were already dead 16 hours after LPS. In contrast, only 33% of fetuses were dead 16 hours after LPS (P =.001) when NAC was given. LPS was followed by a reduction in maternal (LPS: 26.3 nmol/mg [95% CI 19.9-32.8] vs CRL: 41.3 nmol/mg [95% CI 34.7-47.9, P <.01]) and fetal GSH (LPS: 19.7 nmol/mg [95% CI 11.7-27.8] vs CRL: 34.5 nmol/mg [95% CI 32.0-37.0, P <.001]). This decline was reversed by NAC (NAC/LPS maternal GSH: 37.0 nmol/mg [95% CI 22.5-51.5] and fetal GSH: 28.4 nmol/mg [95% CI 22.8-33.9]). Importantly, maternal liver GSH impacted on fetal survival. NAC/LPS mothers with living pups 16 hours after LPS had significantly higher liver GSH compared with NAC/LPS mothers whose pups died in utero. In fact, all NAC-treated mice whose hepatic GSH exceeded 20 nmol/mg had living fetuses at 16 hours.

CONCLUSION

Maternal inflammation in C57Bl/6 mice results in oxidative stress associated with maternal and fetal GSH depletion. Oxidative stress damages the fetus independent of prematurity. Restoration of maternal and fetal oxidative balance by NAC protects the fetus and reduces the rate of preterm birth.

Chorion-induced myometrial relaxation is mediated by large-conductance Ca2+-activated K+ channel opening in the guinea pig

OBJECTIVE

We previously demonstrated that chorion releases a factor that inhibits both spontaneous and oxytocin-stimulated myometrial contractility. Here, we investigate the mechanism of action of this unidentified substance.

STUDY DESIGN

Myometrial strips from pregnant guinea pigs were mounted in an organ bath and contractility stimulated with oxytocin.

RESULTS

Guinea pig chorion produced a time-dependent decrease in oxytocin-induced myometrial contractility. The ability of the chorion to reduce contractility was unaltered by inhibiting chorionic synthesis of either nitric oxide (N [omega]-nitro-L-arginine), carbon monoxide (tin-protoporphyrin), prostaglandins (indomethacin), or the myometrial cyclic guanosine monophosphate pathway (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalime-1-one and Rp-8Br-cGMP). In contrast, iberiotoxin, an inhibitor of large conductance Ca(2+)-activated K(+) channels reduced the quiescent effect of chorion by 40%; in contrast, inhibition of adenosine triphosphate-sensitive (glibenclamide) and voltage-gated K(+) channels (4amynopyridine) had no effect.

CONCLUSION

Chorion-induced relaxation of oxytocin-stimulated myometrial contraction is, in great part, the product of a paracrine substance that opens myometrial large conductance Ca(2+)-activated K(+) channels.

Application of ductus venosus Doppler velocimetry for the detection of fetal aneuploidy in the first trimester of pregnancy

OBJECTIVE

To test the hypothesis the application of ductus venosus Doppler velocimetry may serve as a screening tool between 10 and 14 weeks' gestation for the detection of fetuses with chromosomal abnormalities.

METHODS

372 consecutive fetuses were studied. Based on prior study, a chromosomal abnormality was suspected when either the nuchal translucency was above the 95th centile, or there was reversed or absent flow in the ductus venosus during atrial contraction. Sensitivity, specificity, and the negative and positive predictive values were calculated.

RESULTS

There were 29 chromosomally abnormal fetuses. Of these 29 fetuses, ductus venosus blood flow during atrial contraction was either absent (n = 2) or reversed (n = 25) in 93.1%. In the chromosomally normal fetuses (n = 343), only 6 (1.7%) had abnormal Doppler profiles in the ductus venosus (specificity = 98.3%, positive and negative predictive values = 81.8% and 99.4%, respectively).

CONCLUSION

The Doppler waveform of the ductus venosus was at least equal to NT thickness measurement for the detection of chromosomal abnormalities.

Effects of sublingual nitroglycerin on human uterine contractility during the active phase of labor

Nitroglycerin is administered intravenously in acute obstetric emergencies to relax the uterus. However, complications (eg, hypotension, acute uterine bleeding) are frequent, which prompted a search for alternative routes of administration. We hypothesized that the sublingual administration of nitroglycerin would reduce uterine tone and contractility with few complications. Intrauterine pressure was measured in 12 women who were actively laboring (>4 cm dilatation, regular contractions) with epidural analgesia and who were alert and responsive throughout the study. In a double-blind fashion, subjects were randomized to receive either placebo or sublingual nitroglycerin (3 doses, 800 microg each) 10 minutes apart. The obstetric anesthesiologist continuously monitored maternal blood pressure and fetal heart rate. Cervical dilatation was assessed at the beginning and the end of the protocol. The area under the intrauterine pressure curve (integral) was used to estimate uterine contractility. Intrauterine pressure was analyzed before the randomization code was broken. Nitroglycerin did not alter the intrauterine pressure integral after the first dose (placebo, 3147 mm Hg x s [95% CI, 2206-4088] vs nitroglycerin, 4146 mm Hg x s [95% CI, 2451-5841]; P =.22), second dose (placebo, 3123 mm Hg x s [95% CI, 2447-3799] vs nitroglycerin, 3611 mm Hg x s [95% CI, 2723-4499]; P =.28), or third dose (placebo, 3303 mm Hg x s [95% CI, 2616-3990] vs nitroglycerin, 3810 mm Hg x s [95% CI, 2306-5314]; P =.45). Cervical dilation, basal uterine tone, duration and frequency of uterine contractions, or fetal heart rhythm remained unaffected. Maternal mean arterial pressure decreased significantly after nitroglycerin was administered. All women were delivered vaginally without intervention. Three doses of sublingual nitroglycerin (800 microg per dose) reduce neither uterine activity nor tone, despite lowering maternal blood pressure. If a clinical option, sublingual nitroglycerin will require a higher dose, which would place mother and fetus at risk for complication.

Pushing in labor: performance and not endurance

OBJECTIVE

It is believed that delivery is faster if women are instructed to voluntarily bear down in synchrony with their uterine contractions. Confronted by the large variance in the duration of the second stage of labor, many clinicians attribute a "fast" or a "short" expulsion time solely to the patient's willingness to cooperate or to the strength of epidural anesthesia if it is a factor. Yet, knowledge of pushing performance and the factors affecting it remain limited. We investigated the maternal, fetal, and labor characteristics that influence the maternal "pushing performance" and sought to design a predictive index that prospectively identified "high" versus "low" pushing performers.

STUDY DESIGN

Intrauterine pressure (IP) was prospectively measured during the second stage of labor in 52 women recruited at one North American hospital. Recordings were begun after documentation of full cervical dilatation and descent of the fetal head to +2 station (on a -3/+3 scale). Each woman acted as her own control, received epidural anesthesia, and was alert and responsive throughout the study. Pushing (closed glottis technique) was performed in a standardized fashion. Multivariate analysis with linear regression was applied to identify significant associations between maternal, fetal, or labor characteristics as the independent variables and the percent increase in IP consequent to active pushing as the dependent variable.

RESULTS

Women in labor increase their IP 62% by actively pushing with a contraction during the second stage. A scattergram of the individual percent increase above the baseline IP integral revealed that for some women, pushing more readily increased their IP than it did for others (range, 0% to 192%). The percent increase was best calculated by a linear combination of myometrial thickness, estimated fetal weight, the maternal body mass index, and the obstetric need for labor augmentation (P =.007, r = 0.52, power = 0.975). A 66% change in IP provided the best separation between high and low pushing performance. Myometrial thickness provided the single strongest contribution to the regression equation's predictive value (P =.01, r = -0.36). A myometrial thickness of 6 mm had a specificity of 88% (but only 53% sensitivity) for the identification of women able to increase their IP by 66% over baseline.

CONCLUSIONS

In women in labor who have received epidural anesthesia, the efficiency with which maternal expulsive efforts are converted into increased IP is directly related to the patient's body mass index but inversely related to myometrial thickness, the sonographic estimate of fetal weight, and the need for labor augmentation.

The effect of fundal pressure manoeuvre on intrauterine pressure in the second stage of labour

OBJECTIVE

To investigate the relationship between intrauterine pressure and the application of a standardised fundal pressure manoeuvre, and to determine the maternal, fetal and labour characteristics that modulate the relationship.

DESIGN

Prospective measurement of intrauterine pressure during the second stage of labour.

SETTING

North American university hospital.

POPULATION

Forty full-term women in spontaneous labour were studied during the second stage. Each woman acted as her own control. All women laboured with requested epidural analgesia.

METHODS

A fundal pressure manoeuvre was performed so as to standardise the level of force and the surface area of application. Intrauterine pressure was measured using a sensor-tip catheter. Five interventions were analysed: 1. valsalva during a uterine contraction; 2. fundal pressure and valsalva during a contraction; 3. fundal pressure during a contraction without valsalva; 4. fundal pressure in the absence of uterine contractions; and 5. valsalva in the absence of uterine contractions.

RESULTS

Women in the second stage of labour transiently increased their expulsive force (as reflected by intrauterine pressure) by 86% of their baseline contraction using valsalva and fundal pressure simultaneously. The efficiency by which both contraction-enhancing manoeuvres increased intrauterine pressure was directly related to gestational age and inversely related to myometrial thickness.

CONCLUSION

Fundal pressure applied under controlled conditions significantly increases intrauterine pressure in some, but not all women. Simultaneous measurement of intrauterine pressure, to maintain feedback during application will create a 'controlled environment' for the obstetrician and reassurance that this manoeuvre can be applied in a controlled fashion. Future delineation of the group of women that could benefit from fundal pressure, as well as the group that is refractory is essential to avoid unnecessary or delayed operative interventions.

Pregnancy and estradiol decrease GTPase activity in the guinea pig uterine artery

The mechanisms by which pregnancy redistributes cardiac output in an organ-specific manner are poorly understood. We propose that it is consequential to estrogen-mediated alterations in G protein-mediated signal transduction. Aortas and uterine (UAs) and mesenteric arteries (MAs) were obtained from late-pregnant, nonpregnant, or ovariectomized guinea pigs chronically treated with 17beta-estradiol. High-affinity GTPase activity was assayed enzymatically. The cGMP generated in response to the endothelium-dependent agonist ACh was measured in UAs incubated with or without cholera toxin (CTX, which inhibits G(s)alpha). Pregnancy significantly decreased UA but not aorta or MA GTPase activity. 17beta-Estradiol decreased UA GTPase activity compared with untreated ovariectomized animals. ACh increased cGMP in pregnant but not nonpregnant UAs. Pretreatment of nonpregnant UAs with CTX increased ACh-induced cGMP levels similar to pregnancy. Thus pregnancy and estradiol decrease the GTPase activity of a CTX-sensitive G protein in UAs, increasing receptor-dependent cGMP release. This alteration in receptor-mediated G protein coupling in UAs may contribute to the characteristic cardiovascular adaptation to pregnancy.

Use of McRoberts' position during delivery and increase in pushing efficiency

McRoberts' position is used during the second stage of labour to facilitate delivery of the fetal shoulders. Few clinical studies have been done to measure its efficacy. We measured intrauterine pressure in 22 women in term labour, after the vertex reached 3+ station, in the dorsal lithotomy position. Patients pushed with legs either in stirrups or hyperflexed by 1358 (McRoberts' position). Maternal valsalva transiently increased the expulsive force by 32% over naturally occurring contractions. Use of McRoberts' position almost doubled the intrauterine pressure developed by contractions alone (from 1653 mm Hg s to 3262 mm Hg s [97%]).

Leveraging healthcare for the greater good: lessons learned from the National Centers of Excellence in Women's Health

The creation of the National Centers of Excellence in Women's Health (CoE) program in 1996 by the Office on Women's Health, Department of Health and Human Services, included the stipulation that each institution awarded a CoE contribute at least a 25% match for the federal funds. Even the combination of these two sources of monies was insufficient for each CoE to accomplish its goals, however, so leveraging funds became necessary for each CoE to function effectively. The forms of leveraging varied from CoE to CoE, in part as a result of the institutional environment and the unique possibilities each permitted and in part as a result of the creativity of the leaders of the CoEs. This paper describes the concepts and some applications of leveraging in the setting of the CoEs, which might be applicable to other settings as well.

Pregnancy enhances G protein activation and nitric oxide release from uterine arteries

We hypothesized that pregnancy modulates receptor-mediated responses of the uterine artery (UA) by altering G protein activation or coupling. Relaxation and contraction to NaF (0.5-11.5 mM), acetylcholine (10(-9)-10(-5) M), and bradykinin (10(-12)-3 x 10(-5) M) were measured in isolated UA of pregnant and nonpregnant guinea pigs. Responses were measured in the presence and absence of either cholera toxin (2 microg/ml) or pertussis toxin (Galpha(s) and Galpha(i) inhibitors, respectively). NaF relaxation was endothelium dependent and nitro-L-arginine sensitive (a nitric oxide synthase inhibitor). Relaxation to NaF, acetylcholine, and bradykinin were potentiated by pregnancy. Cholera but not pertussis toxin increased relaxation to acetylcholine and bradykinin in UA from nonpregnant animals, had no effect in UA from pregnant animals, and abolished the pregnancy-induced differences in acetylcholine relaxation. Cholera toxin potentiated the bradykinin-induced contraction of UA of both pregnant and nonpregnant animals, whereas pertussis toxin inhibited contraction of UA from pregnant animals only. Therefore, pregnancy may enhance agonist-stimulated endothelium-dependent relaxation and bradykinin-induced contraction of UA by inhibiting GTPase activity or enhancing Galpha(s) but not Galpha(i) activation in pregnant animals. Thus the diverse effects of pregnancy on UA responsiveness may result from hormonal modulation of G proteins coupled to their specific receptors.

Endotoxemia causing fetal bradycardia during urosepsis

BACKGROUND

Fetal bradycardia is a recognized response to maternal hypothermia associated with hypoglycemia, tocolysis with magnesium sulfate, or urosepsis, and it is thought to be a direct response to the decrease in the maternal core temperature.

CASE

A 25-year-old white woman, gravida 1, para 0, at 31 1/7 weeks' gestation was admitted with a diagnosis of pyelonephritis. The baseline fetal heart rate was 120 beats per minute with accelerations. Within 3 hours of admission, the patient became hypothermic (35.1C) and, concomitantly, the fetal heart rate baseline declined to 90 beats per minute with marked variability. Despite sustained maternal hypothermia, the fetal heart rate baseline rose to 120 beats per minute. It was another 6 hours before the patient's temperature rose above 38.5C. Her urine and blood cultures were positive for Serratia rubidacea infection. The patient delivered a healthy infant at 39 weeks' gestation.

CONCLUSION

Fetal bradycardia in the presence of urosepsis might be due to the release of endotoxin from gram-negative bacteria, triggering production of cardiotoxic cytokines, rather than to maternal hypothermia alone.

Chorion releases a factor that inhibits oxytocin-stimulated myometrial contractility in the pregnant guinea pig

It was postulated that chorion releases a substance necessary for the maintenance of uterine quiescence during pregnancy. A decrease in the release of this substance at the end of the pregnancy would be necessary for normal myometrial activation. This hypothesis was tested by demonstrating the ability of chorion to inhibit oxytocin-stimulated myometrial contractility in vitro. Tissues were obtained from timed pregnant Duncan-Hartley guinea pigs either at pre-term or near-term gestation. Myometrial strips were placed in organ baths for isometric tension measurement and contractions stimulated by oxytocin (10(-8) mol/l). Fetal membranes or conditioned medium from chorion were added directly to the organ bath. Near-term chorion and chorion conditioned-medium decreased oxytocin-stimulated contractile activity to 39% and 49% respectively. Neither pre-term nor near-term amnion reduced oxytocin-stimulated myometrial contractile activity. Relaxation induced by pre-term chorion was greater than near-term chorion (23% and 41% of the oxytocin-induced basal level respectively; P < 0.05). Further, chorion-induced relaxation was independent of the gestational age of the myometrium. Human chorion from a term, not-in-labour woman also inhibited oxytocin-stimulated guinea pig myometrial contractility. It was concluded that the chorion releases a substance or substances that reduce oxytocin-stimulated myometrial contractility and may be involved in the maintenance of uterine quiescence during pregnancy.

Natriuretic peptide-induced relaxation of myometrium from the pregnant guinea pig is not mediated by guanylate cyclase activation

We tested both relaxation and cGMP generation by atrial (ANP), brain (BNP), and C-type natriuretic peptide (CNP) in oxytocin-stimulated myometrium from near-term pregnant guinea pigs to investigate the ability and mechanism of natriuretic peptides to inhibit myometrial contractility. Myometrial strips were contracted by 10(-8) M oxytocin, and relaxation to the cumulative addition (10(-9)-10(-6) M) of the natriuretic peptides measured. Maximal relaxation to BNP was significantly greater than to ANP (52 versus 32% respectively; p < 0.05), whereas CNP failed to produce relaxation. However, the increase in cGMP produced by BNP (10(-7) M) was significantly less than that produced by ANP (10(-7) M) (4.5 versus 7.0 times basal; p < 0.05); CNP did not increase myometrial cGMP. Anantin, a competitive blocker of the guanylate cyclase A receptor, significantly reduced the increase in cGMP produced by ANP and BNP, but had no effect on relaxation induced by either peptide. Rp-8-Br-cGMP, an inhibitor of the cGMP-dependent protein kinase, did not alter BNP-induced relaxation. The atrial natriuretic peptide-fragment 4-23 amide, a natriuretic peptide clearance receptor agonist, failed to inhibit oxytocin-stimulated myometrial contraction. We conclude that natriuretic peptide induced relaxation of oxytocin-stimulated myometrium from the pregnant guinea pig is not mediated by either guanylate cyclase A or B activation, is independent of the cGMP pathway, and does not involve clearance receptor activation. Our results suggest that natriuretic peptide-induced relaxation of pregnant myometrium is mediated via a novel mechanism.

Application of a functional genomics approach to identify differentially expressed genes in human myometrium during pregnancy and labour

The molecular mechanisms regulating uterine relaxation and contraction during pregnancy are poorly understood. In the present study, we used for the first time a functional genomics approach applying gene array technology to identify novel candidate genes involved in the regulation of uterine quiescence and contractility during pregnancy. The purpose of this approach was to obtain a molecular snapshot of the expression profile of gene transcripts as a function of the time dependent process regulating myometrial quiescence. Using this approach, we found several genes whose expression in human myometrium was altered with the onset of labour. For example, the expression of insulin-like growth factor (IGF)-II, calgranulin A and B, and G-protein coupled receptor were decreased while the expression of IGF-binding proteins, Ca(2+)/CaM binding protein kinase C substrate, and angiotensin converting enzyme were increased in the labouring, compared with non-labouring, pregnant myometrium. The differentially-expressed genes include several genes whose roles in myometrial quiescence are yet to be understood, although they have been reported to regulate vascular smooth muscle tone. Our findings illustrate the advantage of a functional genomics approach over a single gene analysis in identifying a large number of novel and potentially important genes mediating uterine smooth muscle contractile activity.

Differential alterations in responsiveness in particulate and soluble guanylate cyclases in pregnant guinea pig myometrium

OBJECTIVE

The mechanism underlying myometrial quiescence during pregnancy is unknown. Our group has previously shown that during pregnancy myometrial cyclic guanosine monophosphate content rises to several hundred times the nonpregnant levels, only to abruptly decline days before the onset of labor. Cyclic guanosine monophosphate plays an integral role in the relaxation of smooth muscle. The aim of this investigation was therefore to determine the effects of pregnancy on both soluble and particulate guanylate cyclase enzymatic activities and messenger ribonucleic acid expressions.

STUDY DESIGN

Myometrium was obtained from randomly cycling adult nonpregnant guinea pigs and near-term (50-60 days' gestation) pregnant guinea pigs of similar chronologic age. Subcellular fractions were prepared by differential ultracentrifugation. Guanylate cyclase activity was determined by the conversion of guanosine triphosphate to cyclic guanosine monophosphate under basal or stimulated conditions in either the soluble guanylate cyclase or particulate guanylate cyclase fraction. A nitric oxide donor, S-nitroso- N-penacillamine, was used to activate soluble guanylate cyclase (n = 10 animals in each group). Several natriuretic peptides (atrial natriuretic peptide, brain natriuretic peptide, and C-type natriuretic peptide) and uroguanylin were used to stimulate the different particulate guanylate cyclase isoforms guanylate cyclase A, guanylate cyclase B, and guanylate cyclase C, respectively, in pregnant (n = 8) and nonpregnant (n = 6) animals. Cyclic guanosine monophosphate content was measured by radioimmunoassay, and enzymatic activity was expressed as picomoles of cyclic guanosine monophosphate per milligram of protein per minute. Total guanylate cyclase represented the sum of soluble guanylate cyclase and particulate guanylate cyclase activities for a tissue. To investigate whether the observed changes in guanylate cyclase activity were paralleled by changes in receptor expression, messenger ribonucleic acid levels of the genes for guanylate cyclase A and guanylate cyclase B isoforms were quantified by ribonuclease protection assay (n = 5 animals in each group).

RESULTS

Under basal conditions particulate guanylate cyclase represented 78% (nonpregnant state) to 88% (during pregnancy) of the total guanylate cyclase activity in the guinea pig myometrium. Pregnancy further reduced myometrial soluble guanylate cyclase (both basal and stimulated by nitric oxide) relative to the nonpregnant state. Pregnancy selectively increased atrial natriuretic peptide-stimulated particulate guanylate cyclase activity (attributed to guanylate cyclase A), although it did not change basal myometrial particulate guanylate cyclase activity in general. Guanylate cyclase B (particulate guanylate cyclase stimulated by C-type natriuretic peptide) and guanylate cyclase C (particulate guanylate cyclase stimulated by uroguanylin) activities were unaltered by pregnancy. The selective increase in responsiveness of particulate guanylate cyclase to atrial natriuretic peptide during pregnancy was not paralleled by an increased in level of messenger ribonucleic acid for the gene for guanylate cyclase A.

CONCLUSION

Pregnancy reduced the in vitro responsiveness of the myometrial soluble guanylate cyclase to nitric oxide while increasing the responsiveness of the particulate isoform to atrial natriuretic peptide and brain natriuretic peptide through a mechanism independent of any change in receptor expression.

Chronic hypoxia increases the NO contribution of acetylcholine vasodilation of the fetal guinea pig heart

To investigate the effect of chronic hypoxia (HPX) on vasodilation of the fetal heart, we exposed pregnant guinea pigs to room air or 12% O(2) for 4, 7, or 10 days. We excised hearts from anesthetized fetuses (60 +/- 3 days; 65-day gestation = term) and measured changes in both the coronary artery pressure of the isolated constant-flow preparation and endothelial nitric oxide synthase (eNOS) mRNA of fetal ventricles. Dilator responses to cumulative addition (10(-9)-10(-5) M) of acetylcholine and sodium nitroprusside in prostaglandin F(2alpha) (5 x 10(-6) M)-constricted hearts were similar among normoxia (NMX), 4-, 7-, and 10-day HPX (control). Nitro-L-arginine (L-NA, 10(-4)M), a NOS inhibitor, inhibited maximal acetylcholine dilation of hearts exposed to 10-day HPX greater than NMX, 4-, and 7-day HPX. Hypoxia (after 7 and 10 days) increased eNOS mRNA of fetal ventricles compared with NMX and 4-day HPX. 4-Aminopyridine (3 mM), a voltage-dependent K(+)-channel inhibitor, inhibited acetylcholine- but not sodium nitroprusside-induced dilation of NMX and 10-day HPX hearts to a similar magnitude. Glibenclamide (10(-5) M), an ATP-sensitive K(+)-channel inhibitor, had no effect on vasodilation. We conclude that chronic HPX increases the contribution of NO but does not alter K(+)-channel activation in response to acetylcholine-stimulated coronary dilation. Thus increases in NO production via upregulation of eNOS gene expression may be an adaptive response to chronic HPX in the fetal coronary circulation.

Coronary artery blood flow visualization signifies hemodynamic deterioration in growth-restricted fetuses

OBJECTIVE

To determine the relationship between fetal coronary blood flow (CBF) visualization in intrauterine growth restriction (IUGR), longitudinal changes in arterial and venous flow velocity waveforms and perinatal outcome.

METHODS

A total of 48 IUGR fetuses (abdominal circumference below the 5th percentile for gestational age) with absent or reversed umbilical artery (UA) end-diastolic velocity (AREDV) were examined longitudinally by echocardiography attempting CBF visualization at each examination. Doppler evaluation of the middle cerebral artery, inferior vena cava (IVC), ductus venosus (DV) and umbilical vein (UV) was performed at each examination. Doppler measurements were correct for gestational age by conversion into Z-scores (delta-indices). Doppler results and outcome from fetuses in which CBF was visualized (group 1, n = 20) and those in which CBF was never visualized (group 2, n = 28) were compared. Outcome parameters analyzed included Apgar scores, cord arterial blood gases, perinatal mortality, respiratory distress, bronchopulmonary dysplasia, intraventricular hemorrhage, necrotizing enterocolitis and postpartum circulatory failure requiring pressor support.

RESULTS

There was no difference in Doppler indices between groups at study entry. CBF visualization coincides with a significant increase of UA-, IVC- and DV delta-indices. The greatest rate of change was observed for indices in the ductus venosus which occurred in the 24 h preceding CBF visualization. Group 1 fetuses required earlier delivery (median 27 + 4, vs. median 30 + 0), had lower birthweight (682 +/- 305 g vs. 936 +/- 416 g), lower cord pH (7.21 +/- 0.1 vs. 7.27 +/- 0.06) and cord pO2 (13 +/- 4.5 vs. 24.1 +/- 13.5 mmHg) compared to group 2 (all values P < 0.05). Mortality was similar (group 1 = 6/20, 30%; group 2 = 6/28, 21.4%).

CONCLUSIONS

In IUGR, fetuses with AREDV and centralization are at high risk for hypoxemia, acidemia and adverse outcome. CBF visualization coincides with deteriorating venous flows. Operator dependence of CBF visualization and the strong association with abnormal venous flow stresses the importance of venous Doppler surveillance in these fetuses.

Relationship between arterial and venous Doppler and perinatal outcome in fetal growth restriction

OBJECTIVE

The aim of this investigation was to assess the relationship between abnormal arterial and venous Doppler findings and perinatal outcome in fetuses with intrauterine growth restriction (IUGR).

METHODS

Doppler velocimetry of the umbilical artery (UA), middle cerebral artery (MCA), inferior vena cava (IVC), ductus venosus (DV) and free umbilical vein was performed in 121 IUGR fetuses with a UA pulsatility index (PI) > 2 SD above the gestational age mean and subsequent birth weight < 10th centile for gestational age. Groups based on the last Doppler exam were: 1 = abnormal UA-PI only (n = 42, 34.7%), 2 = MCA-PI > 2 SD below the gestational age mean (= 'brain sparing') in addition to abnormal UA-PI (n = 29, 24.0%), 3 = DV or IVC peak velocity index (PVIV) > 2 SD above the gestational age mean and/or pulsatile UV flow (n = 50, 41.3%). Z-scores (delta indices) were calculated for Doppler indices. Perinatal mortality, respiratory distress (RDS), bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH), necrotizing enterocolitis (NEC), circulatory failure and umbilical artery blood gases were recorded.

RESULTS

Absence or reversal of umbilical artery end-diastolic flow was observed in 4 (9.5%) of fetuses in group 1, 10 (34.5%) fetuses in group 2 and 41 (82%) fetuses in group 3. A low middle cerebral artery pulsatility index was found in 39 (78%) fetuses in group 3. Multiple regression analysis with gestational age at delivery, delta indices and cord artery blood gas as independent parameters and individual perinatal outcomes as dependent variables was performed. In this analysis the association was strongest with gestational age for each complication. There were no significant differences in Apgar scores between groups. At delivery, 'brain sparing' was associated with hypoxemia and abnormal venous flows with acidemia. Perinatal mortality was highest in group 3 and stillbirth was only observed when venous flow was abnormal. All postpartum complications were more frequent in fetuses with abnormal venous flows. The only statistically significant relation between Doppler indices and outcome was the association between abnormal ductus venosus flow and fetal death (r2 = 0.24, P < 0.05).

CONCLUSION

Growth restricted fetuses with abnormal venous flow have worse perinatal outcome compared to those where flow abnormality is confined to the umbilical or middle cerebral artery. In fetuses with low middle cerebral artery pulsatility, venous Doppler allows detection of further deterioration. While abnormal venous flows can be significantly associated with fetal demise, gestational age at delivery significantly impacts on all short-term outcomes.

Molecular mechanism of cGMP-mediated smooth muscle relaxation

Contraction and relaxation of smooth muscle is a tightly regulated process involving numerous endogenous substances and their intracellular second messengers. We examine the key role of cyclic guanosine monophosphate (cGMP) in mediating smooth muscle relaxation. We briefly review the current art regarding cGMP generation and degradation, while focusing on the recent identification of the molecular mechanisms underlying cGMP-mediated smooth muscle relaxation. cGMP-induced SM relaxation is mediated mainly by cGMP-dependent protein kinase activation. It involves several molecular events culminating in a reduction in intracellular Ca(2+) concentration and a decrease in the sensitivity of the contractile system to Ca(2+). We propose that the cGMP-induced decrease in Ca(2+) sensitivity is a strategic way to achieve "active relaxation" of the smooth muscle. In summary, we present compelling evidence supporting a key role for cGMP as a mediator of smooth muscle relaxation in physiological and pharmacological settings.

Absent umbilical artery end-diastolic velocity in growth-restricted fetuses: a risk factor for neonatal thrombocytopenia

OBJECTIVE

To examine the relationship between umbilical artery (UA) end-diastolic flow and neonatal thrombocytopenia.

METHODS

We prospectively examined 115 anatomically normal single fetuses with UA pulsatility indices more than two standard deviations above the gestational age mean and subsequent birth weights below the tenth percentile. Peripheral neonatal platelet counts in fetuses with positive UA end-diastolic velocity were compared with those of fetuses with absent or reversed UA end-diastolic velocity.

RESULTS

Sixty-seven fetuses (58.3%) had positive UA end-diastolic velocity and 48 (41.7%) had absent or reversed UA end-diastolic velocity. Three neonates in the positive-flow group and 22 neonates in the absent- or reversed-flow group had platelet counts of less than 100, 000/mm(3) (relative risk 10.2; 95% confidence interval; 3.2, 32.3; P <.001). Absent or reversed end-diastolic velocity had a sensitivity of 88%, specificity of 71%, positive predictive value of 46%, and negative predictive value of 96% for predicting neonatal thrombocytopenia. Neonates with absent or reversed flow also had lower median platelet counts (101,500/mm(3) versus 208,000/mm(3), P <.001), hemoglobin levels (15.1 versus 16.4 g/dL, P <.01), and hematocrits (47.6 versus 51.1%, P <.05), as well as higher nucleated red blood cell counts (191 versus 15 per 100 white blood cells, P <. 001).

CONCLUSION

Absent or reversed UA end-diastolic velocity in growth-restricted fetuses is associated with a statistically significant increase in risk of neonatal thrombocytopenia.

Chronic 17beta-estradiol replacement increases nitric oxide-mediated vasodilation of guinea pig coronary microcirculation

BACKGROUND

Estrogen is cardioprotective of the coronary circulation by mechanisms incompletely understood. This study determined the effect of chronic 17beta-estradiol replacement on dilator responses to acetylcholine and sodium nitroprusside of the isolated coronary microcirculation.

METHODS AND RESULTS

Adult female guinea pigs were ovariectomized, and a 21-day-release pellet containing 0.0, 0.1, 0.25, 0.5, or 1.0 mg 17beta-estradiol was implanted subcutaneously. Serum estradiol concentrations ranged from 3.9 to 74.9 pg/mL, increasing with the dose of estradiol. After 19 to 20 days, the animals were euthanized, and their hearts were removed and perfused with buffer at constant flow on an isolated heart apparatus. Both perfusion pressure and contractile force were measured in prostaglandin F(2alpha)-constricted hearts. Vasodilation to the cumulative addition of the endothelium-dependent agonist acetylcholine (10(-9) to 10(-5) mol/L) and the nitric oxide (NO) donor sodium nitroprusside (10(-9) to 10(-5) mol/L) was measured before and after NO synthesis inhibition by nitro-L-arginine (LNA, 10(-4) mol/L). Baseline coronary resistance was unaltered by estradiol, although LNA increased resistance in estradiol-treated hearts more than in ovariectomized controls. Chronic 17beta-estradiol increased sensitivity (measured by -log EC(50) values) but not maximal response to acetylcholine compared with ovariectomized controls. Differences were abolished by LNA at all doses of estradiol. Sodium nitroprusside-induced dilation was unaffected by estradiol replacement.

CONCLUSIONS

Chronic 17beta-estradiol replacement, at doses producing hormone levels within the physiological range, enhances dilator sensitivity of the coronary microcirculation through enhanced NO production by the endothelium, independent of changes in NO sensitivity of the vascular smooth muscle. Thus, estradiol enhances NO production as a protective mechanism of the coronary microcirculation.