Myometrial arginase activity increases with advancing pregnancy in the guinea pig

OBJECTIVES

Arginase has been suggested to play an important role in cellular growth and development, particularly important to the fetus, by supplying L-ornithine for the synthesis of polyamines. The purpose of this investigation was to determine whether pregnancy alters myometrial arginase activity and whether estradiol was responsible for the change.

STUDY DESIGN

Myometrium and kidney were obtained from nonpregnant and pregnant guinea pigs of known gestational age. Arginase activity was measured under physiologic conditions by the conversion carbon 14-labeled guanidino-L-arginine to carbon 14-labeled urea. The concentrations of the enzyme's substrate, L-arginine, and its principal metabolite, L-ornithine, were measured in myometrium from near-term pregnant animals by use of an amino acid analyzer. Finally, a group of random cycle guinea pigs received 500 microgram/kg estradiol for 5 days before the myometrium was removed.

RESULTS

Myometrial arginase activity in pregnant animals was more than double that of myometrium from nonpregnant animals by the time the first measurement was made at 0.14 gestation. It continued to rise, peaking at values >25-fold higher than the nonpregnant activity by 0.90 gestation. Arginase activity in the myometrium underlying the placental implantation site was >25 fold higher (p<0.05) than myometrium from nonpregnant animals when first studied at 0.63 gestation and 10-fold higher than the contralateral fundal myometrium at the same time of gestation. Myometrial arginase activity in the sterile horn of six pregnant animals was half that of the horn containing one or more pups, but still five times higher than that of nonpregnant animals. Renal arginase activity also rose with advancing pregnancy, but the magnitude of the increase (up to 2-fold) was much smaller than that observed in either the fundal or placental implantation site myometrium. Estradiol had no significant effect on myometrial arginase activity.

CONCLUSIONS

These studies demonstrate that pregnancy increases myometrial arginase activity and that the presence of placenta or fetus is necessary for the maximal effect.

Decreased fetal erythropoiesis and hemolysis in Kell hemolytic anemia

OBJECTIVE

Lower changes in optical density (450 nm) measurements have been reported in fetuses with anti-Kell anemia compared with those anti-D anemia. The purpose of this investigation was to determine if hemolysis and erythropoiesis differ between anti-Kell and anti-D hemolytic disease.

STUDY DESIGN

Ninety-three pregnancies complicated by either anti-D or anti-Kell alloimmunization were evaluated. Fetal blood samples obtained at the first cordocentesis were tested for the red blood cell antigen type, hemoglobin, hematocrit, reticulocyte count, nucleated red blood cells, total serum bilirubin concentration, umbilical venous respiratory blood gases, serum erythropoietin level, and strength of the direct Coombs test. To determine the evolution of hemolytic anemia in the two antigen groups, these laboratory parameters were repeated on the fetal blood samples triggering the decision to perform a fetal intravascular transfusion (hematocrit <30%).

RESULTS

A total of 65 of 93 fetuses were antigen positive (11 for Kell and 54 for RhD). The mean gestational age and laboratory measurements of antigen- positive, nonanemic fetuses at first blood sampling did not differ significantly between groups. There was a strong inverse relationship observed between the hemoglobin concentration and reticulocyte count independent of gestational age in the anti-D group but not in the anti-Kell group. Eight (73%) fetuses with anti-Kell antibodies and 37 (69%) with anti-D antibodies underwent intravascular transfusion. At the cordocentesis when the decision for transfusion was made, anti-Kell anemic fetuses had lower reticulocyte counts and total bilirubin concentrations. The strong inverse relationship between the hemoglobin and reticulocyte count was again seen only in the anti-D group. In both groups, fetal erythropoietin increased significantly between the first and last blood samplings and in each group were negatively correlated with hemoglobin independent of gestational age.

CONCLUSION

Anti-Kell anemic fetuses have lower reticulocyte counts and total serum bilirubin levels than do comparable anti-D anemic fetuses. This finding argues in favor of fetal blood sampling rather than amniotic fluid analyses for the management of fetal hemolytic disease resulting from Kell antibodies. Unlike RhD alloimmunized fetuses, these fetuses do not manifest an inverse relationship between hemoglobin concentration and reticulocyte count. We speculate that compared to anti-D fetal anemia, anti-Kell anemia is associated with increased hemolysis of nonhemoglobinized or incompletely hemoglobinized erythroid precursors.

Expression and localization of inducible and endothelial nitric oxide synthase in the rat ovary. Effects of gonadotropin stimulation in vivo

Nitric oxide is reportedly involved in the regulation of several ovarian processes, yet the isoforms of nitric oxide synthase (NOS) expressed in the ovary are unknown. Our purpose was to identify and localize NOS isoenzymes in the rat ovary and to examine++ if mRNA expression of NOS isoenzymes change after gonadotropin stimulation. Using reverse transcriptase-PCR, we demonstrated that inducible (iNOS) and endothelial (eNOS), but not neuronal, NOS mRNAs are expressed in the ovary. In a gonadotropin-stimulated rat model, unstimulated ovaries had the highest levels of iNOS mRNA as quantified by ribonuclease protection assay. After gonadotropin injection, iNOS mRNA declined to undetectable levels in ovaries containing ovulatory follicles before increasing slighty in ovaries containing copora lutea. In situ hybridization studies localized iNOS to granulosa cells of secondary follicles and small antral follicles. Western blots of unstimulated ovaries demonstrated iNOS protein. In contrast to iNOS, eNOS mRNA levels, determined by quantitative PCR, increased after gonadotropin stimulation and peaked in ovaries containing ovulatory follicles before declining in the luteal phase. eNOS protein was localized to blood vessels in the ovary by immunohistochemistry. We conclude that two isoforms of NOS are expressed in the ovary and the mRNA levels for these isozymes are differentially regulated.

Fetal blood sampling and fetal thrombocytopenia

The purpose of this investigation is to determine whether fetal thrombocytopenia is a risk factor for puncture site bleeding. Three groups of fetuses either with or at known risk for thrombocytopenia were identified from a prospectively maintained data base of 1,100 procedures: alloimmune thrombocytopenia (ATP, 29 cordocenteses); unexpected thrombocytopenia (53 cordoncenteses), and intravascular transfusion for fetal hemolytic anemia (194 transfusions). A fourth group (58 cordocenteses) included as a normal control consisted of all appropriately grown fetuses tested within the same gestational age range as those with ATP. In total, 276 fetal blood sampling procedures were included, of which 134 (49%) yielded a platelet count of < 120 x 10(3)/microliters and 38 (14%) a platelet count of < 50 x 10(3)/microliters. The first platelet count obtained from fetuses with ATP ranged from 1 x 10(3) to 159 x 10(3)/microliters. There was no correlation between the platelet count and bleeding time whether the analysis was limited to only pretreatment procedures or included all. Each fetus with unexpected thrombocytopenia was systemically ill. There was no correlation between platelet count and the duration of bleeding from the cord puncture site. Intravascular transfusion produced a significant decline in the platelet count (238 +/- 66 x 10(3) vs. 153 +/- 56 x 10(3)/microliters, p < 0.001). Twenty-nine percent of the post-transfusion platelet counts were below 120 x 10(3)/microliters. There was a significant negative correlation between the final platelet count and the duration of puncture site bleeding (r = -0.178, p = 0.03) independent of either the presence of hydrops, the initial or the increase in the umbilical venous pressure during transfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Congenital infection

The past year has shed much new light on congenital infection. A key development has been the application of polymerase chain reaction technology to the diagnosis of intrauterine infection. This technique appears to be the diagnostic tool of choice for toxoplasmosis and cytomegalovirus. Pharmacologic treatment appears to reduce the sequellae of toxoplasmosis when treated either in utero or postnatally. Obstetric interventions may reduce vertical transmission. Education has been shown to reduce the incidence of seroconversion for toxoplasmosis, and HIV-positive women treated with zidovudine have a dramatically reduced rate of transmission to their offspring.

Growth deficient fetuses with absent or reversed umbilical artery end-diastolic flow are metabolically compromised

Controversy continues regarding the clinical relevance of absent or reversed umbilical artery blood flow during diastole. The purpose of this study was to characterize the blood gas and lactate measurements of growth deficient fetuses with absent (ADF) or reversed (RDF) umbilical artery (UA) diastolic flow. In a descriptive study from February 1988 through October 1991, 42 consecutive structurally and karyotypically normal growth deficient fetuses identified to have either ADF or RDF diastolic flow in the UA were studied. Heparinized blood specimens were obtained from them and the pH, PCO2, PO2 and lactate measured. Fourteen of these specimens were obtained from the umbilical vein by cordocentesis and 28 at the caesarean delivery of non-labouring patients. Statistical analyses were performed using Fisher's exact test, Student t-test and linear correlation. All measured parameters in fetuses with ADF or RDF undergoing cordocentesis were significantly abnormal compared to gestational age corrected norms. Both the mean venous and arterial pH of fetuses with RDF were significantly lower than that of fetuses with ADF. With few exceptions, preoperative maternal oxygenation failed to correct the fetal hypoxaemia associated with either ADF or RDF. In the setting of severe fetal growth deficiency secondary to uteroplacental dysfunction, ADF and RDF are clinically reliable indicators of fetal compromise as determined by the umbilical blood gases. RDF is associated with a greater impairment of placental gas exchange than ADF.

Regionalization of endothelium-dependent relaxation in the thoracic aorta of pregnant and nonpregnant guinea pigs

Regional variation in the response of the thoracic aorta to contractile agonists has previously been demonstrated. Since the net contractile response reflects the interaction between smooth muscle activation and the release of endothelial substances, we hypothesize that agonist-stimulated release of endothelium-derived nitric oxide (NO) also varies along the length of the thoracic aorta. The distribution of thoracic aorta estrogen receptors is also regionalized. Since pregnancy augments the release of endothelium-derived NO by acetylcholine (ACh) in some arterial beds, we further hypothesize that pregnancy enhances the stimulated release of NO from the thoracic aorta. Aortae were removed from nonpregnant and near term pregnant guinea pigs and cut into ring segments numbered sequentially proximal to distal. The rings were suspended at their optimal passive tension and submaximally contracted with prostaglandin F2 alpha. Endothelium-derived NO-dependent relaxation to ACh increased moving proximal to distal along the aorta independent of pregnancy and ACh relaxation was unaffected by pretreatment with physostigmine to inhibit cholinesterase. The magnitude of the relaxation to carbachol among the different segments was similar to ACh. Pregnancy decreased the ED50 for ACh of segments from the middle and distal segments of the thoracic aorta. Relaxation to the NO donor sodium nitroprusside and the nonreceptor-mediated endothelium-dependent relaxing agent A23187 was uniform along the length of the aorta and independent of pregnancy. These experiments demonstrate regional variation in the stimulated release of endothelium-derived NO in the guinea pig thoracic aorta which is increased by pregnancy.

Pregnancy increases guanosine 3',5'-monophosphate in the myometrium independent of nitric oxide synthesis

The mechanism for myometrial quiescence during pregnancy is unknown. cGMP plays an integral role in the relaxation of smooth muscle, and nitric oxide (NO) is the most important endogenous activator of soluble guanylate cyclase. The purpose of this study was to determine the effect of gestational age on myometrial cGMP and NO synthase (NOS) activity in the guinea pig. Myometrial cGMP content (measured by RIA) rose slowly until 0.49 (fraction of pregnancy completed) gestation before abruptly increasing to 200 times the non-pregnant control value. It then declined precipitously after 0.87 gestation. Of the known isoenzymes of NOS, the messenger RNAs coding for both endothelial and neuronal NOS could be amplified from the myometrium of pregnant and nonpregnant animals using reverse transcriptase-polymerase chain reaction, but inducible NOS messenger RNA was not found. Myometrial calcium-dependent NOS activity (measured by the conversion of L-[U-14C]arginine to [U-14C]citrulline) declined slowly with advancing gestation (r2 = 0.096; slope = -0.34; P = 0.01), but never differed significantly from the activity in nonpregnant animals [31.1 +/- 11 (term pregnancy) vs. 56.9 +/- 16 (nonpregnant) pmol/min.g; P = NS]. Calcium-independent activity declined shortly after conception, and then rose toward the nonpregnant level (r2 = 0.19; slope = 0.45; P = 0.0009). However, at no time was it significantly different from that in the nonpregnant animal. Pregnancy had no effect on myometrial L-arginine and L-citrulline content. The administration of L-nitro-arginine methyl ester (200 mg/kg) to inhibit NOS dramatically increased blood pressure and reduced fetal renal NOS activity, but had no effect on the myometrial cGMP content. Estradiol (500 micrograms/kg for 5 days) modestly increased cGMP, but in contrast to many tissues in which estradiol increases NOS, it had no effect on myometrial NOS activity. We conclude that pregnancy dramatically increases cGMP by a mechanism independent of NOS. The stimulus remains to be identified. The temporal change in cGMP concentration is consistent with the hypothesis that cGMP mediates myometrial quiescence during pregnancy.

First trimester three-dimensional ultrasound volumetry of the gestational sac

First trimester amniotic fluid is an ultrafiltrate of maternal plasma and constitutes the major component of gestational sac volume (GSV). We hypothesized that GSV, assessed by 3-dimensional (3-D) ultrasound volumetry, would reflect function of the early uteroplacental unit and therefore provide a basis for predicting pregnancy outcome. We tested this hypothesis in 38 pregnancies which had first trimester GSV measurements by two investigators thus allowing determination of interobserver variation. Gestational age (GA) was based on a careful history and conventional 2-dimensional ultrasound measurements. Serum for beta-hCG, estradiol (E2) and progesterone (P) was obtained at the time of ultrasound examinations. "Normal" outcome was defined as confirmation of a viable fetus. "Abnormal outcome" was defined as either a "blighted ovum" or embryonic demise. Statistical analysis was performed by Independent t-test and regression analysis. There were 31 "normal" and 7 "abnormal" pregnancies studied between 5 and 11 weeks gestation (mean +/- SD 8.3 +/- 1.3 weeks). GSV was significantly correlated to GA (r = 0.74, P < 0.001), higher than to beta-hCG (r = 0.40, P = 0.034), E2 (r = 0.70, P < 0.001) and P (r = 0.21, P = 0.334), respectively. In the abnormal group 2/2 pregnancies with a twin sac had a GSV within 1 SD of the mean. 3/5 cases of missed abortions or blighted ovum had a GSV < 2 SD of the mean. The interobserver correlation was high (r = 0.99, P < 0.00f2p4This is the first clinical study investigating the diagnostic use of 3-D ultrasound volumetry in first trimester pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide: an autocrine regulator of human granulosa-luteal cell steroidogenesis

We investigated the presence of nitric oxide (NO) synthase in ovarian follicular cells obtained from women undergoing in vitro fertilization procedures. Endothelial NO synthase messenger RNA was demonstrated by polymerase chain reaction amplification of reverse transcribed RNA. NO synthase was localized to granulosa-luteal cells by immunocytochemistry, using a monoclonal antibody. Ovarian follicular cell NO synthase enzyme activity was confirmed by measuring the conversion of L-arginine to citrulline. To investigate the effect of NO on granulosa-luteal cell steroidogenesis, NO synthase inhibitors and NO donors were added to cell cultures. NG-Monomethyl-L-arginine and N-nitro-arginase methyl ester, selective inhibitors of NO synthase, significantly increased estradiol secretion by granulosa-luteal cells. S-Nitroso-L-acetyl penicillamine (S-NAP) and S-nitroso glutathione, NO donors, caused a dose-dependent decrease in both estradiol and progesterone secretion. The decrease by S-NAP was reversed by hemoglobin, which binds free NO. Although S-NAP increased the concentration of cGMP in granulosa-luteal cells, cGMP analogs had no effect on steroidogenesis in cell cultures. S-NAP and native NO in solution decreased cellular and microsomal aromatase activities. We conclude that NO synthase is present in human granulosa-luteal cells and that NO inhibits estradiol secretion independent of cGMP by directly inhibiting aromatase.

Diagnosis, pathophysiology, and treatment of chronic twin-to-twin transfusion syndrome

The discovery of a 'stuck twin' during an ultrasound examination has often been equated with twin-to-twin transfusion based to a great extent on postnatal confirmation of discordant fetal size and hemoglobin concentration. However, the diagnosis of twin-to-twin transfusion cannot be made with certainty after birth since virtually all monochorionic gestations have placental anastomoses and there are many causes of growth deficiency and abnormal hemoglobin concentration. The purpose of this study is to investigate the pathophysiology of chronic twin-to-twin transfusion syndrome and apply the findings to the development of a management algorithm. In 42 twin gestations with stuck twin associated with acute hydramnios, we performed targeted ultrasound cordocentesis in each fetus and therapeutic amniocentesis. The diagnosis of chronic twin-to-twin transfusion syndrome required: sonographic evidence of monochorionicity; rapid reaccumulation of fluid after amniocentesis; discordant fetal size, and divergent fetal hematocrit measurements with at least one above or below the 95% confidence interval for gestational age. These criteria were met in 20 of 42 (48%) pregnancies. The mean gestation was 23.8 +/- 2 weeks (range 21-27 weeks). In 4 pregnancies, the transfer of adult RBCs from the donor to the recipient was documented. Monochorionicity was confirmed in all postnatally. All recipients had polycythemia and hyperproteinemia. Hydrops developed only in the recipient twin (6 of 20) and was associated with an elevated umbilical venous pressure. All pregnancies were treated with aggressive serial therapeutic amniocenteses. There was no objective evidence that amniocentesis altered the magnitude of the shunt.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of nitric oxide synthases early in pregnancy

OBJECTIVE

We have previously demonstrated that calcium-dependent nitric oxide synthase is induced by estrogen and that by the end of pregnancy nitric oxide synthase of both endothelial and neuronal origin is increased in various maternal tissues. This rise in activity may be crucial for the alterations in muscle activity necessary for a successful pregnancy. If so, the increase in nitric oxide synthase activity must occur early in gestation.

STUDY DESIGN

We tested the hypothesis that pregnancy increases nitric oxide synthase activity early in gestation by measuring in heart, kidney, skeletal muscle, and esophagus of time-mated guinea pigs the conversion by nitric oxide synthase of carbon 14-labeled L-arginine to carbon 14-labeled citrulline and the concentration of cyclic guanosine monophosphate, the second messenger of nitric oxide.

RESULTS

Calcium-dependent nitric oxide synthase activity was increased twofold to fourfold by pregnancy in each tissue examined. The rise began by 0.14 gestation (9 of 63 +/- 2 days) and reached a plateau by 0.30 gestation (19 days), which was then maintained until term. The treatment of pregnant animals with tamoxifen decreased nitric oxide synthase activity to nonpregnant values in the heart, where tamoxifen is an estrogen receptor antagonist, but not in kidney, skeletal muscle, and esophagus. Cyclic guanosine monophosphate also rose progressively in each tissue studied until about 0.70 gestation before declining in skeletal muscle, kidney, and heart. It remained elevated in the esophagus.

CONCLUSION

These studies demonstrate that nitric oxide synthase activity in maternal tissues rises early in pregnancy and is associated with an increase in cyclic guanosine monophosphate, the second messenger of nitric oxide. These findings are consistent with the hypothesis that an increase in nitric oxide synthase plays a role in smooth muscle adaptations of pregnancy.

Effect of pregnancy on contraction and endothelium-mediated relaxation of renal and mesenteric arteries

We have hypothesized that differences in the effect of pregnancy on mechanisms modulating vascular reactivity underlie the redistribution of cardiac output. Because pregnancy increases mesenteric blood flow by 75% and renal blood flow by only 10% in the guinea pig, we investigated the effect of pregnancy on vascular reactivity in these two beds. Relaxation in response to acetylcholine (ACh), an endothelium-dependent relaxing agent, and contraction induced by the thromboxane mimetic U-46619 were measured in ring segments of mesenteric and renal arteries from pregnant and nonpregnant guinea pigs. To determine the role of the endothelium, nitric oxide (NO), and vasodilator prostaglandins in modulating vascular response, rings were denuded, treated with N omega-nitro-L-arginine (L-NNA) to inhibit NO synthase, or treated with indomethacin to inhibit cyclooxygenase. Pregnancy increased ACh-stimulated relaxation of mesenteric arteries but not renal arteries. L-NNA significantly reduced ACh sensitivity (based on the concentration that produced 50% of the maximal response) in arteries from pregnant and nonpregnant animals, and indomethacin slightly decreased maximal relaxation only in the renal artery of nonpregnant animals. ACh sensitivity of mesenteric arteries was still increased after L-NNA or indomethacin. Pregnancy reduced the threshold concentration of U-46619 in mesenteric artery but had no effect on contraction of renal artery. Contraction of both arteries was enhanced by denudation. L-NNA and indomethacin were less effective than denudation in arteries from pregnant and nonpregnant animals, which suggests that pregnancy alters thromboxane contraction by endothelium-dependent mechanisms other than NO and prostaglandins. Thus, pregnancy differentially alters vascular reactivity of mesenteric and renal arteries in the guinea pig.

Outcome of alloimmunized fetuses managed solely by cordocentesis but not requiring antenatal transfusion

A published algorithm for the frequency of fetal blood sampling in the management of fetal hemolytic disease allows many pregnancies to continue 1-3 months after the last sample until delivery at term. Though the positive predictive value for antenatal anemia is known, the likelihood of either neonatal hyperbilirubinemia or an unexpected anemia (< 30%) is not. The perinatal records of 51 antigen-positive neonates who did not require treatment antenatally were abstracted. As fetuses, these neonates had been prospectively coded as either low risk (pattern 1), moderate risk (pattern 2) or high risk (patterns 3 and 4) for antenatal anemia (hematocrit < 30%) based on their hematocrit, reticulocyte count, and the strength of the direct Coombs' test performed on their first sample. Delivery occurred at 38 +/- 2 weeks. Neonatal complications of hemolytic disease were common. Sixty-four percent required phototherapy, 17% one or more double-volume exchange transfusions, and 13% one or more simple transfusions for late-developing anemia. In all, 29% of neonates received postnatal transfusion therapy. The only correlation between the antenatal hematologic/serologic studies and the need for postnatal transfusion therapy was the strength of the indirect Coombs' test performed on the first fetal blood sample. Two neonates unexpectedly had anemia (4% risk). In the first, the hematocrit at 35 weeks was 40% and the ultrasound 1 week later normal. In one, the algorithm had been erroneously applied. Stability of the hematocrit in fetuses at risk to develop antenatal anemia can be accurately predicted by fetal blood tests performed weeks prior to delivery.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct relationship of fetal carboxyhemoglobin with hemolysis in alloimmunized pregnancies

Because carbon monoxide (CO) is a byproduct of heme degradation and because placental diffusing capacity of CO is limited, we hypothesized that the concentration of CO transported in fetal blood as carboxyhemoglobin (HbCO) would correlate with the severity of fetal hemolytic disease. Fetal blood was obtained by cordocentesis and HbCO was measured by gas chromatography. The two primary study groups included control fetuses (n = 26) and fetuses of Coombs-positive mothers before in utero transfusion (n = 15). Compared with controls, fetuses with hemolytic disease had higher HbCO levels (0.0111 +/- 0.0014 versus 0.0159 +/- 0.0072 fraction of total Hb, mean +/- SD, p < 0.002). In contrast, HbCO levels in simultaneously sampled maternal blood samples were not different in the control and alloimmune groups [0.0110 +/- 0.0025 (n = 20) versus 0.0115 +/- 0.0021 (n = 11)]. There was a significant inverse correlation observed between fetal HbCO and Hb concentrations in the group with hemolytic disease (r = -0.73, p < 0.002) but not in controls. In fetuses with hemolytic disease, HbCO and bilirubin were highly correlated (r = 0.88, p < 0.0001). Data from four anemic fetuses who were Coombs negative, three of whom had no evidence of hemolysis, indicated normal HbCO and normal plasma bilirubin levels. A fourth fetus with anemia had viral sepsis and elevated HbCO and plasma bilirubin levels. We conclude that elevated HbCO levels detected in fetuses of nonsmoking mothers with erythrocyte alloimmunization are likely the result of accelerated hemolysis.

Induction of calcium-dependent nitric oxide synthases by sex hormones

We have examined the effects of pregnancy and sex hormones on calcium-dependent and calcium-independent nitric oxide synthases (NOSs) in the guinea pig. Pregnancy (near term) caused a > 4-fold increase in the activity of calcium-dependent NOS in the uterine artery and at least a doubling in the heart, kidney, skeletal muscle, esophagus, and cerebellum. The increase in NOS activity in the cerebellum during pregnancy was inhibited by the estrogen-receptor antagonist tamoxifen. Treatment with estradiol (but not progesterone) also increased calcium-dependent NOS activity in the tissues examined from both females and males. Testosterone increased calcium-dependent NOS only in the cerebellum. No significant change in calcium-independent NOS activity was observed either during pregnancy or after the administration of any sex hormone. Both pregnancy and estradiol treatment increased the amount of mRNAs for NOS isozymes eNOS and nNOS in skeletal muscle, suggesting that the increases in NOS activity result from enzyme induction. Thus both eNOS and nNOS are subject to regulation by estrogen, an action that could explain some of the changes that occur during pregnancy and some gender differences in physiology and pathophysiology.

MR of fetal central nervous system abnormalities

PURPOSE

To investigate whether MR can provide additional information on fetuses with central nervous system abnormalities as demonstrated by ultrasonography.

METHODS

Fetal MR examinations were studied prospectively in 22 pregnant women whose fetuses showed evidence of anomalies on ultrasound performed in the High-Risk Obstetric Clinic.

RESULTS

In 19 of 22 cases, postpartum confirmatory diagnoses were obtained by MR or CT examinations, autopsy, or surgery. In general, the image quality of MR is comparable with that of ultrasound. However, in six of 22 cases (27%), MR provided additional information that altered the ultrasound diagnosis; these included cases of infarction, diastematomyelia, normal hemimegalencephaly with early myelination, Dandy-Walker variant, and lipoma. All of these cases had postpartum confirmation. The additional information changed the treatment in three of six patients (no intervention or elective abortion).

CONCLUSIONS

In certain situations MR can add valuable information to that obtained by sonography in the evaluation of the fetal central nervous system.

Fetal echogenic bowel on ultrasound: is there clinical significance?

Though echogenic fetal bowel has been associated with meconium ileus and/or peritonitis, it may be a normal finding in the second trimester. The purpose of this study is to determine which characteristics might distinguish fetuses ultimately having abnormal outcomes in a population at low risk for cystic fibrosis. Seven fetuses with echogenic bowel were identified: 5 fetuses < or = 20 weeks gestation (group 1) and 2 fetuses 20-25 weeks gestation (group 2) at diagnosis. Four of 5 group 1 fetuses had resolution of the echogenic bowel during the second trimester. One group 2 fetus had a persistent mass associated with growth deficiency and trisomy 18. The neonatal bowel evaluation was normal in the remaining 2 fetuses although echogenic findings persisted into the third trimester. In a low-risk population, echogenic bowel usually resolves without neonatal sequelae. Even when persistent into the third trimester, echogenic bowel does not uniformly herald an abnormal outcome. Echogenic bowel coexistent with other abnormalities (such as growth deficiency or structural malformations) may be a comarker for aneuploidy.

Effect of intravenous beta-sympathomimetic tocolysis on human fetal serum erythropoietin levels

OBJECTIVE

The major stimulus for erythropoietin production is tissue hypoxia. We sought to investigate the relationship of beta-sympathomimetic administration for tocolysis and fetal serum erythropoietin.

STUDY DESIGN

Umbilical cord blood was obtained from infants whose mothers received intravenous beta-sympathomimetic tocolysis and who were delivered at < or = 34 weeks' gestation. Serum erythropoietin was measured by radioimmunoassay. On the basis of the presumed 2- to 4-hour half-life of fetal erythropoietin, the infants were divided into two groups. In group 1 (n = 16) beta-sympathomimetic therapy was discontinued < 24 hours before delivery; in group 2 (n = 11) it was discontinued > or = 24 hours before delivery.

RESULTS

Group 1 fetuses had significantly higher erythropoietin levels than did group 2 fetuses (37.3 vs 13.9 mU/ml, p = 0.02). The duration of beta-sympathomimetic tocolysis and the maximum infusion rate were not different. The two groups did not differ in gestational age, birth weight, route of delivery, presence of labor, or duration of first or second stage of labor.

CONCLUSIONS

We speculate that intravenous beta-sympathomimetic tocolytic therapy stimulates fetal erythropoietin production by decreasing fetal oxygenation as a result of the reversible fetal metabolic effects of the tocolysis. These data suggest that beta-sympathomimetic tocolysis should be undertaken cautiously if fetal compromise is suspected, fetal well-being should be assessed carefully if tocolysis is undertaken, and treatment should be discontinued promptly if a clear benefit is not realized.

Endothelium-derived relaxing factor inhibits norepinephrine contraction of fetal guinea pig arteries

As in the adult circulation, the endothelium may play an important role in determining fetal vascular tone. The purpose of this study was to determine the influence of the endothelium on norepinephrine- and phenylephrine-induced contraction of pulmonary and carotid arteries from near-term fetal guinea pigs. Isometric contractions of isolated rings to the cumulative addition of norepinephrine (10(-9)-10(-5) M) were measured before and after 1) endothelium removal, 2) NG-monomethyl-L-arginine (L-NMMA; 10(-4) M) to inhibit endothelium-derived relaxing factor (EDRF), 3) methylene blue (10(-5) M) to inhibit guanylate cyclase, 4) oxyhemoglobin (3 x 10(-6) M) to bind EDRF, and 5) indomethacin (10(-5) M) to inhibit cyclooxygenase. All treatment effects were measured in endothelium-intact segments. The maximal norepinephrine contraction of fetal pulmonary (40 +/- 8% KCl, n = 7) and carotid (13 +/- 7% KCl, n = 7) arteries was much less (P < 0.05) than the maximal contraction to 120 mM KCl. Treatments that inhibit the action of EDRF increased contraction of both fetal pulmonary and carotid arteries. L-NMMA also increased contraction to phenylephrine. Indomethacin had no effect on the contractile responses to norepinephrine of either artery. Thus EDRF inhibits alpha-adrenoceptor-stimulated contraction of fetal pulmonary and carotid arteries and may attenuate the constrictor responsiveness of the fetal circulation in vivo.

Umbilical pressure measurement in the evaluation of nonimmune hydrops fetalis

OBJECTIVE

Nonimmune hydrops fetalis continues to have a perinatal mortality rate > 50%. Although many abnormalities are associated with nonimmune hydrops fetalis, the direct mechanism by which the hydrops occurs is often obscure, even after delivery. There are at least three possible mechanisms for hydrops: heart failure (whether primary or a secondary effect of obstructed venous return), lymphatic malformation, and liver or peritoneal disease. The development of safe access to the fetal circulation by cordocentesis allows for the measurement of the umbilical venous pressure, which is closely related to the fetal central venous pressure. The premise that nonimmune hydrops fetalis of cardiac origin could be distinguished from that of noncardiac origin was examined by measuring the umbilical venous pressure.

STUDY DESIGN

Umbilical venous pressure was measured during indicated diagnostic cordocentesis in three groups of fetuses: 20 with nonimmune hydrops fetalis, four with a cardiac malformation but without nonimmune hydrops fetalis, and eight with immune hydrops (fetal hemolytic disease). In 16 of 20 fetuses with nonimmune hydrops fetalis the serum total protein and albumin concentrations were also measured.

RESULTS

Presumed inadequate cardiac output, as indicated by an elevated umbilical venous pressure, was the mechanism of nonimmune hydrops fetalis in 13 of 20 (65%). The pathologic condition included arrhythmia, cardiothoracic abnormalities, severe polycythemia and hyperviscosity, viral infection, and severe anemia. Successful antenatal treatment normalized the umbilical venous pressure. Nonimmune hydrops fetalis secondary to noncardiac mechanisms did not progress in severity and was not amenable to antenatal therapy. Hypoproteinemia and hypoalbuminemia were found in only six of 16 cases and were similarly distributed between cardiac and noncardiac mechanisms.

CONCLUSIONS

This is the first report where the measurement of umbilical venous pressure was applied to the evaluation of nonimmune hydrops fetalis. Cardiac dysfunction was the most common mechanism causing hydrops. The finding of a normal umbilical venous pressure greatly reduces the likelihood that the heart is the cause of the hydrops, even when there is a coexistent heart malformation. This immediate information allows the practitioner either to focus on therapeutic interventions that might lower the umbilical venous pressure or to look for noncardiac causes for the hydrops.

"Normal" umbilical arterial and venous acid-base and blood gas values

Study groups often considered representative of entire populations inevitably do not consider normal fetuses because nonpathologic events can alter the study parameters. Therefore, the term "normal" and its range, when used for comparisons, must be scrutinized by the obstetrician, pediatrician, and those with medicolegal concerns.

Diagnosis of fetal infection in the patient with an ultrasonographically detected abnormality but a negative clinical history

Unsuspected fetal infection (viral or parasitic) is often overlooked as a possible cause of abnormalities revealed on ultrasonographic examination during pregnancy. Infectious agents can produce a wide spectrum of ultrasonographic findings. Our objective was to highlight those findings and review the rationale and method of antenatal investigation. No ultrasonographic findings are pathognomonic for a particular agent. The search for possible fetal infection consists of both direct and indirect techniques. Methods to directly demonstrate fetal infection include maternal-fetal serologic studies, culture, electron microscopy, and polymerase chain reaction. Emerging evidence strongly suggests that prior assumptions concerning the sensitivity of both maternal and fetal-neonatal serologic studies are incorrect. Serologic studies alone are inadequate to exclude fetal infection as a cause of an ultrasonographically detected abnormality. Indirect techniques suggestive of fetal infection include fetal hematologic and biochemical measurements. New approaches and methods for the detection of fetal infection are needed. The evaluation should be initiated antenatally. Needless delay until after delivery increases the likelihood that the diagnosis will be missed. Antenatal diagnosis provides the opportunity for therapy and often leads the practitioner to modify the obstetric and neonatal care plan. A protocol used by the University of Iowa Fetal Diagnosis and Treatment Unit for the diagnosis and management of unsuspected fetal infection is offered as an example of a protocol that has been successful in the past.