Human Na(+)-dependent vitamin C transporter 1 (hSVCT1): primary structure, functional characteristics and evidence for a non-functional splice variant.

We report here on the cloning and functional characterization of human Na(+)-dependent vitamin C transporter 1 (SVCT1). The human SVCT1 cDNA, obtained from a Caco2 cell cDNA library, encodes a protein of 598 amino acids with 12 putative transmembrane domains. The SVCT1-specific transcript, 2.4 kb in size, is expressed in kidney, liver, small intestine, thymus and prostate. When expressed heterologously in HRPE cells, SVCT1 mediates the transport of ascorbate, the reduced form of vitamin C, in a Na(+)-dependent manner. The transporter is specific for ascorbate with a K(t) of approximately 75 microM. The relationship between the cDNA-specific uptake rate of ascorbate and Na(+) concentration is sigmoidal with a Na(+):ascorbate stoichiometry of 2:1, indicating that the transport process is electrogenic. In Caco2 cells and in normal human intestine, SVCT1 also exists as a non-functional splice variant with a four amino acid sequence inserted between E-155 and V-156. The splice variant results from the use of a donor site 12 bp downstream of the normal donor site.

Cloning and functional characterization of a Na(+)-independent, broad-specific neutral amino acid transporter from mammalian intestine.

We have isolated a cDNA from a rabbit intestinal cDNA library which, when co-expressed with the heavy chain of the human 4F2 antigen (4F2hc) in mammalian cells, induces system L-like amino acid transport activity. This protein, called LAT2, consists of 535 amino acids and is distinct from LAT1 which also interacts with 4F2hc to induce system L-like amino acid transport activity. LAT2 does not interact with rBAT, a protein with a significant structural similarity to 4F2hc. The 4F2hc/LAT2-mediated transport process differs from the 4F2hc/LAT1-mediated transport in substrate specificity, substrate affinity, tissue distribution, interaction with D-amino acids, and pH-dependence. The 4F2hc/LAT2-associated transport process has a broad specificity towards neutral amino acids with K(t) values in the range of 100-1000 microM, does not interact with D-amino acids to any significant extent, and is stimulated by acidic pH. In contrast, the 4F2hc/LAT1-associated transport process has a narrower specificity towards neutral amino acids, but with comparatively higher affinity (K(t) values in the range of 10-20 microM), interacts with some D-amino acids with high affinity, and is not influenced by pH. LAT2 is expressed primarily in the small intestine and kidney, whereas LAT1 exhibits a much broader tissue distribution.

Interaction of clonidine with human placental Na+ -H+ exchanger.

The effect of clonidine, an alpha 2-adrenergic receptor agonist, on the Na+ -H+ exchanger in human placental brush-border membrane vesicles was examined. The exchanger was inhibited by clonidine. The inhibition was freely reversible, and the apparent inhibition constant for the process was 250 microM. The nature of inhibition was found to be competitive with respect to Na+. The Dixon plot (1/v versus clonidine concentration) was linear (r2 = 0.998), indicating the interaction of the drug with a single site on the exchanger protein. Similar kinetic analyses with amiloride, a potassium-sparing diuretic, and cimetidine, a histamine type II receptor antagonist, revealed that these drugs also inhibited the Na+ -H+ exchanger by interacting with a single site on the protein. The presence of clonidine increased the intercepts without affecting the slopes of the l/v versus amiloride concentration and the l/v versus cimetidine concentration plots. These results demonstrate that all three drugs, amiloride, cimetidine and clonidine, interact with the human placental Na+-H+ exchanger at a single site in a mutually exclusive manner, and the site of interaction is identical with the Na+-binding site on the external surface of the exchanger protein.

Clinical features of the reactive positive contraction stress test.

During a five-year period, 2815 patients undergoing 5685 fetal heart rate (FHR) tests produced 147 positive contraction stress tests. Baseline FHR patterns were considered reactive if three or more accelerations occurred during 30 minutes of the contraction stress test and nonreactive if fewer or no accelerations were noted. There were 75 reactive positive contraction stress tests and 72 nonreactive positive contraction stress tests. Both groups were promptly delivered, generally (91%) within 24 hours of the last test. Fetuses producing reactive positive patterns tended to be more mature, larger, and most frequently tested for postmaturity. Fetuses with nonreactive positive patterns had significantly higher rates of perinatal mortality and morbidity, growth retardation, and cesarean deliveries; they were frequently carried by hypertensive mothers. Each group was analyzed according to deceleration: contraction ratio, and deceleration: contraction ratio deciles from 30 to 100% were examined. Perinatal complications increased progressively with higher deceleration: contraction ratios, irrespective of baseline reactivity; however, nonreactive fetuses in any deceleration: contraction ratio decile had more frequent perinatal compromise than their reactive counterparts. The lack of specificity (26 poor outcomes in 75 cases) associated with the reactive positive contraction stress tests encourages more frequent attempts at vaginal delivery; in this group, 64 of 71 patients had successful vaginal deliveries. Furthermore, the high incidence of good fetal outcome in the reactive positive group suggests that the urgency of delivery in such circumstances be reassessed and that other fetal-maternal indicators be considered in delivery decisions.

Antepartum fetal heart rate testing in preterm pregnancy.

The nonstress test (NST) and the contraction stress test (CST) have had wide application to term pregnancies, but little has been reported of use in the management of preterm fetuses. Seventy-two of 438 high-risk gravidas, receiving both tests between 25 and 34 weeks' gestation, delivered singleton infants before completion of their 34th week. On the basis of the last NST and CST preceding delivery, the 72 fetuses could be divided into reactive-negative and nonreactive-positive groups. Nonreactive-positive fetuses experienced greater perinatal mortality and significantly higher rates of intrapartum fetal distress, neonatal depression, respiratory distress syndrome (RDS), intrauterine growth retardation, and cesarean section. Pulmonary complications in nonreactive-positive fetuses, regardless of the lecithin: sphingomyelin ratio, were significantly increased if intrapartum fetal distress had preceded delivery. Most neonatal deaths stemmed from RDS-related complications, 86% preceding the 31st week of gestation; however, nearly half of the perinatal deaths before the 30th week followed reactive NSTs. The data suggest that for clinical management of preterm pregnancy, fetal heart rate testing should be initiated after the 29th week; earlier, test significance is less clear and infant survival less likely. Maternal estriol determinations aid little in the management of nonreactive-positive fetuses. Rather, the care of these selected pregnancies should be temporized through the 30th week; when delivery is then elected, intrapartum fetal distress should be avoided through liberal use of cesarean section in the nonreactive-positive group.

Serum complement levels and perinatal outcome in pregnancies complicated by systemic lupus erythematosus.

Previous reports suggest an association between maternal serum complement component (C3 and C4) levels and perinatal outcome. Eighteen women with systemic lupus erythematosus (21 pregnancies) were prospectively studied. C3 and C4 levels were measured monthly unless more frequent data were needed for acute medical management. Perinatal outcome was then correlated with both maternal clinical and serologic status before and during pregnancy. Twelve pregnancies were carried to term, 11 of which began in clinical remission. Eight of these 12 had normal C3 and C4 levels at the onset of pregnancy, and 11 were normal at delivery. Four pregnancies were delivered prematurely (with one neonatal death from septic meningitis); all began pregnancy in clinical remission but three had low C3 and C4 levels before delivery. Three pregnancies beginning in clinical remission ended in spontaneous first- or early second-trimester abortions; all had low C3 and C4 levels before aborting. Normal complement component levels were observed in the remaining two pregnancies that were terminated electively; they had no evidence of fetal or placental abnormality. The correlation of maternal serum complement levels and pregnancy outcome in this series suggests that these parameters may help in the assessment of fetal as well as maternal prognosis in lupus-complicated gestations.

Simultaneous nonstress fetal heart rate testing in twin pregnancy.

Twenty-four sets of twins in the third trimester of pregnancy underwent 120 simultaneously recorded nonstress tests (NSTs). Synchronous patterns of fetal heart rate alterations occurred in 58% of the cases and were associated with single placentas and small weight differences between twins. Reactive NSTs were frequent (77%) and, when they occurred within 1 week of delivery, conferred a good prognosis, ie, no perinatal deaths and low morbidity. Nonreactive NSTs were associated with both fetal deaths and a perinatal morbidity of 28%. simultaneous NSTs for twins are technically feasible in the third trimester. They confer a reliable prognosis when reactive; nonreactive tests are less specific and require further investigation.

Does the onset of spontaneous labor at term influence fetal biophysical test parameters?

Recent data suggest that fetal breathing movement incidence declines while fetal heart rate (FHR) and body movement incidence do not change within 72 hours of spontaneous term labor. We conducted a retrospective study to determine whether the length of time from testing to spontaneous labor onset could influence these biophysical test parameters. Eighty-one normal term fetuses underwent 60-minute tests 1-40 days before the onset of spontaneous labor: 41 were tested within 7 days of labor (19 within 3 days and 22 within 4-7 days) and 40 were tested more than 7 days before labor. We simultaneously acquired and analyzed FHR baseline, frequency of accelerations between ten to 14 beats per minute and more than 15 beats per minute in amplitude, percent of time spent in breathing and moving, and fetal breath rate. These biophysical parameters were not significantly different between the groups, implying that they may continue to provide clinically useful information in the prelabor period.

Intrauterine pressure catheter performance in an in vitro uterine model: a stimulation of problems for intrapartum monitoring.

OBJECTIVE: To compare pressure recordings from fluid-filled and sensor-tip catheters under varying intrauterine conditions in a uterine model. METHODS: The uterine model was a 4.1-L dual-walled polyurethane bladder with ports for dual catheter insertion. "Contractions," generated by a programmable pump, were analyzed by computer. The first three experiments used an internal volume of normal saline and included either "normal" catheter placement, distal end of the catheter coated with petroleum jelly, or distal end of the catheter kinked at 150 degrees. The fourth and fifth experiments were similar to the first except that the internal volume was either pea soup or bovine blood. Each study had at least 20 consecutive pressure waveform sequences with peaks of 100, 60, and 20 mmHg, and a resting baseline of 10 mmHg. Ascent and descent phases were each 25 seconds. Peak and baseline pressure phases were each 10 seconds. RESULTS: Each catheter generated satisfactory pressure waveforms, which were similar in all experiments except for the one involving simulated meconium. In this trial, significant waveform damping occurred when pea soup filled the fluid catheter line (P < .05, t test). CONCLUSIONS: In most extreme experimental conditions, the catheter types behaved similarly when detecting "intrauterine" pressure. The sole exception, thick meconium simulation, suggests that fluid-filled catheters would be less reliable in this condition unless flushed continuously with saline.

Can fetal biophysical observations anticipate outcome in preterm labor or preterm rupture of membranes?

OBJECTIVE: To evaluate fetal biophysical testing as a predictor of preterm delivery after preterm labor or preterm rupture of the membranes (PROM). METHODS: We studied 50 women with suspected preterm labor and intact membranes and 25 women with PROM but not in labor between 28 and 36 weeks' gestation. Before treatment, each subject had cervical Bishop scoring and 1-hour ultrasound observation of fetal heart rate, breathing, body movements, and flexion-extensions. Data were compared with t tests, chi 2 tests, or receiver operating curves. RESULTS: The mean gestational age at entry was similar in both groups. Twenty (80%) PROM and ten (18%) preterm labor patients delivered within 72 hours of admission; two (8%) PROM and 38 (76%) preterm labor patients delivered more than 7 days after admission. Absent breathing and body movements had high positive predictive values (100%) but moderate sensitivities (less than 55%) for predicting delivery within 72 hours or 7 days in the PROM and preterm labor groups. These sensitivities increased to nearly 70% with the addition of Bishop scores. The optimal diagnostic cutoffs for delivery within 72 hours or 7 days were a breathing incidence below 1% for the PROM group and a body movement incidence below 1% for the preterm labor group, and a breathing incidence of at most 5%. CONCLUSIONS: Complete absence of one biophysical variable confers limited sensitivity but high positive predictive value for early delivery in patients with preterm labor or PROM. The use of cutoff percentages for the incidence of individual variables improved sensitivity for both conditions. Cervical scoring added to biophysical monitoring by improving the sensitivity for early delivery of patients in preterm labor.

Nonstress test: dimensions of normal reactivity.

Despite the widespread use of the nonstress test, there has been no consensus on the criteria for normal reactivity. The authors studied 495 nonstress tests of 230 normal term fetuses, using a standardized protocol. The frequency distribution of movement-associated fetal heart rate (FHR) accelerations exceeding 15 beats per minute and 15 seconds' duration was examined in windows, ranging from ten to 40 minutes. Mean, median, and modal frequencies of movement-associated FHR accelerations were determined in 1910, 1418, 895, and 473 windows of ten, 20, 30, and 40 minutes, respectively. No significant difference in movement-associated FHR acceleration frequency was observed for any sequential ten-minute window, but movement-associated FHR accelerations were absent in 19.5, 8.8, 5.2, and 5.0% of 10-, 20-, 30-, and 40-minute windows, respectively. The broad frequency distributions of movement-associated FHR accelerations, produced by normal fetuses, precludes discrete diagnostic cutoffs in short time windows, unless one is willing to accept significant negative predictive errors.

Clinical significance of fetal tachypnea during antepartum biophysical testing.

Fetal tachypnea has been regarded as a rare finding with a poor perinatal prognosis. Eighteen cases of fetal tachypnea were noted during the biophysical tests of 200 patients. Biophysical testing consisted of concurrent ultrasound observations of fetal breathing and body movements and electronic monitoring of fetal heart rate, coupled with determinations of fetal tone and amniotic fluid volume. Fetal breathing movement frequency and rate, fetal trunkal movement frequency, and baseline fetal heart rate were analyzed on a programmed microcomputer. The mean (+/- SD) breathing rate was 68.2 +/- 6.4 breaths per minute; mean breathing frequency, 55 +/- 22.6%; mean baseline heart rate, 141 +/- 8 beats per minute; mean trunkal movement incidence, 5.5 +/- 2.6%; and mean acceleration frequency, 14.6 +/- 9.8 per hour. No fetus was apneic for more than eight minutes, and there were no significant correlations between fetal breath rates and the other biophysical parameters. There were no perinatal deaths. Seven fetuses experienced perinatal morbidity, of whom five had other abnormalities on biophysical testing. This study indicates that fetal tachypnea occurs more often than previously believed and does not generally signify fetal compromise unless other biophysical abnormalities are also present.

Maternal plasma D-dimer levels in normal and complicated pregnancies.

OBJECTIVE: To evaluate D-dimer as a marker for fibrinolysis in normal and complicated pregnancies using an enzyme-linked immunosorbent assay (ELISA) technique. METHODS: Four groups of pregnant women were enrolled: 17 normal women followed longitudinally from 28-40 weeks' gestation, 14 patients with preterm labor at 28-34 weeks, 17 patients with preeclampsia at term (37-40 weeks), and 14 patients with abruptio placentae (32-40 weeks). We assayed peripheral venous blood samples from each patient for D-dimer levels using a commercial ELISA kit. D-dimer values were calculated by regression analysis using internal standards and controls for each assay. Data were compared using Student t test or analysis of variance with repeated measures. RESULTS: D-dimer values increased slightly with increasing gestational age. Patients with preterm labor, preeclampsia, and abruptio placentae had mean D-dimer values significantly greater than those of controls (P < .003). D-dimer values of the abruption group were approximately twice those of the control group (3393 +/- 2086 versus 1750 +/- 839 ng/dL). CONCLUSION: An increase in fibrinolysis may be associated with the pregnancy complications studied, as reflected by alterations in maternal plasma D-dimer levels.

The prediction of "controlled" uterine rupture by the use of intrauterine pressure catheters.

OBJECTIVE: To determine whether uterine activity, assessed by either fluid-filled or solid pressure catheters, changes with uterine incision at cesarean delivery. METHODS: Uterine activity was recorded continuously during low transverse cesarean delivery in ten parturients using fluid-filled pressure catheters and in ten women with solid pressure catheters. Visual analyses were performed of the last 30 minutes of uterine recording before uterine incision and of the period after incision; the analyses were then compared within and between the catheter groups for mean uterine tone and contraction amplitude, frequency, and duration. Oxytocin use, anesthesia method, mean gestational age, birth weight, length of labor, duration of monitoring, and uterine incision-to-delivery time were compared between the groups. RESULTS: All obstetric end points were similar in both catheter groups except for a higher mean birth weight in the solid-catheter group. The mean (+/- standard deviation) duration of post-incision monitoring was 4.7 +/- 0.94 minutes. After uterine incision, mean tone and contraction amplitude were unchanged, whereas mean contraction frequency and duration decreased significantly. CONCLUSIONS: Though intrauterine monitoring was brief, this model allows a unique view of "controlled" uterine rupture. Spontaneous uterine rupture may evolve more gradually; however, neither catheter type would be likely to aid its early recognition.

The significance of increasing umbilical artery systolic-diastolic ratios in third-trimester pregnancy.

OBJECTIVE: To evaluate the clinical significance of a marked increase in the systolic-diastolic ratios (S/Ds) of the umbilical artery (UA) Doppler velocity waveforms of third-trimester fetuses. METHODS: We evaluated 552 pregnancies at risk for placental insufficiency. Each patient had at least five successive weekly UA Doppler velocimetry studies between 32-42 weeks and a highest S/D within the normal range for gestational age. The S/D was considered markedly increased if it was at least 20% higher than the mean of four previous values. Clinical end points reviewed included mortality, fetal distress, 5-minute Apgar score below 7, metabolic acidosis, and neonatal intensive care unit (NICU) admissions for reasons other than prematurity. RESULTS: The S/Ds were normal in 478 patients and were markedly increased in 74. The two groups were similar in mean gestational age at testing and delivery and in the rates of fetal growth retardation and low 5-minute Apgar scores. The group without increased S/Ds had a higher mean birth weight and lower incidences of perinatal death, cesarean delivery for fetal distress, acidosis, and NICU admission. The overall sensitivity (43%), specificity (90%), positive predictive value (27%), and negative predictive value (95%) were similar to our previous experience in which we used a criterion of S/D above the 90th percentile. CONCLUSION: Marked increases in UA S/Ds, even if within an institutional "normal" range, may indicate a fetus at increased risk of compromise.

Frequency of asymptomatic bacteriuria in preeclampsia.

Asymptomatic bacteriuria has a reported prevalence of 4 to 7% during pregnancy. Preeclampsia has been reported to increase susceptibility to infection; therefore, the authors examined asymptomatic bacteriuria (greater than 100,000 colonies/mL of urine) as a possible marker for host resistance in preeclamptic pregnancies. One hundred preeclamptic primigravidas at term were compared with 100 nonpreeclamptic primigravidas undergoing primary cesarean section and 100 multigravidas undergoing elective repeat cesarean section. Urine cultures were obtained by bladder catheterization. A significant difference (P less than .005) in the rate of asymptomatic bacteriuria was found in patients with preeclampsia (19%), when compared with that of primigravid (3%), or multigravid (6%) control subjects. Preeclamptic patients with bacteriuria had significantly lower total serum protein and albumin than preeclamptic patients without bacteriuria (P less than .001).

Computerized analysis of resting fetal heart rate tracings.

Previous attempts to computerize the analysis of fetal heart rate (FHR) using mainframe or minicomputers were not accepted in routine clinical practice because of their complexity, cost, and lack of validation. We describe the first practical, inexpensive system integrated into a clinical protocol that analyzes and documents FHR baseline, long-term variability, and episodic events using a standard microcomputer. A comparison of computerized and manual analyses of 284 nonstress tests (NSTs) of high-risk patients revealed no significant differences in determining the number of acceleration and deceleration events and mean FHR baseline. Long-term variability and other reported data could not be compared for lack of manual techniques. The combination of standardized analysis and quantified data may improve the predictive value of the computerized NST compared with the visually analyzed NST. Other benefits include computerized archiving, data transmission by telephone, and linkage to a perinatal data base.

Percent acceleration time: a new method of fetal assessment.

The percent acceleration time (PAT) is a fetal heart rate parameter, which may be derived from the nonstress test (NST). It is based on measurement of the duration of individual movement-associated fetal heart rate accelerations (MAFAs), obtained during a nonstress test, and is calculated by the formula: (formula, see text) The authors studied 148 fetuses undergoing four or more serial nonstress tests who were delivered within one week of their last test. Percent acceleration time of fetuses with normal outcomes had a mean value of 15.5 +/- 10.0 (SD)%, correlated well with the frequency and amplitude of movement-associated fetal heart rate accelerations but was independent of gestational age and mean baseline fetal heart rate. No normal fetus had a percent acceleration time of less than 5% on its last nonstress test, while only one abnormal fetus had a percent acceleration time that exceeded the mean percent acceleration time of the normal group. All abnormal fetuses had a significant progressive decline in percent acceleration time (mean: 50.6%). Percent acceleration time values were more sensitive in identifying fetuses with perinatal compromise than were conventional criteria for nonstress test reactivity, and may provide a useful alternative to assessment of fetal status when other quantitative methods are unavailable (continuous ultrasound visualization) or less reliable (maternal perception, tokodynamometry, palpation).

The effects of epidural anesthesia on the Doppler velocimetry of umbilical and uterine arteries in normal and hypertensive patients during active term labor.

To study the effects of epidural anesthesia on uterine and umbilical artery blood flow in preeclampsia, we observed 25 patients in active labor at 36 or more weeks' gestation. Seven had preeclampsia, eight had chronic hypertension, and ten had no complications. Doppler velocimetry of the uterine and umbilical arteries was performed before and after intravenous fluid loading and at 30 and 60 minutes after epidural blockade. Maternal vital signs and fetal heart rate were monitored continuously. After epidural block, mean maternal blood pressure fell significantly in all groups, but no maternal hypotension was observed. Mean maternal and fetal heart rates were unchanged. After epidural block, mean uterine artery systolic-diastolic (S-D) ratios did not change in the chronic-hypertension and normal groups, but fell significantly in the preeclamptic group to values similar to those of the normal group. Umbilical artery S-D ratios did not change in any group. In preeclamptic pregnancy, epidural anesthesia may help to reduce uterine artery vasospasm and may benefit intrapartum fetal well-being.

The effects of epidural anesthesia on the Doppler velocimetry of umbilical and uterine arteries in normal term labor.

To study the possible effects of epidural anesthesia on the Doppler velocimetry of the fetal umbilical and maternal uterine arteries, 15 normal term parturients were examined during active labor. Each Doppler study, conducted over 90 minutes after a 500-mL intravenous volume pre-load, was divided into three phases: 30 minutes of pre-anesthetic control, 30 minutes during epidural catheter placement and dosing, and 30 minutes after establishing effective regional blockade. During each phase, maternal blood pressure and pulse were monitored every 5 minutes, and continuous-wave Doppler recordings of the umbilical and uterine arteries were made at three separate intervals. Epidural placement and dosage techniques were similar for all patients; 0.25% bupivacaine solution was used and sensory levels of T6 obtained. The mean maternal systolic and diastolic blood pressures and pulse rate declined significantly, but no woman experienced hypotension. Mean systolic/diastolic ratios and pulsatility indices of the umbilical and uterine arteries did not change significantly during the study. We conclude that effective epidural anesthesia does not have a significant impact on Doppler flow characteristics of either the maternal or fetal umbilical vasculature, despite lowered maternal blood pressure and pulse rate.