Role of the L-arginine nitric oxide pathway in hypoxic fetoplacental vasoconstriction.

The role of nitric oxide in hypoxic fetoplacental vasoconstriction (HFPV) was investigated using dually perfused human placental cotyledons. Standard medium (Earle's salt solution with added dextran and L-arginine) was equilibrated with 95 per cent O2 and 5 per cent CO2 (maternal side) and 94 per cent N2 and 6 per cent CO2 (fetal side). Part 1 consisted of perfusion for 1 h, then maternal perfusate equilibrated with a 95 per cent N2 and 5 per cent CO2 for 20 min (hypoxia), and then the original perfusion conditions resumed for 40 min. In part 2, this sequence was repeated with standard medium alone (n = 6), or with added N-nitro-L-arginine methyl ester (L-NAME) (n = 6), or L-NAME and nitroglycerin (n = 6). When standard medium was used throughout, basal fetal perfusion pressure (30 +/- 2 mmHg) and the hypoxia-induced increase in perfusion pressure (18 +/- 1 mmHg) did not change significantly between parts 1 and 2. L-NAME increased basal perfusion pressure from 33 +/- 3 to 56 +/- 2 mmHg whereas perfusion pressure remained unchanged with L-NAME and nitroglycerin or nitroglycerin alone. The hypoxic vasoconstriction observed during part 1 in the L-NAME (14 +/- 3 mmHg) and the L-NAME with nitroglycerin groups (18 +/- 2 mmHg) was abolished during part 2 (to - 4 +/- 1 and 0.4 +/- 0.5 mmHg, respectively) whereas nitroglycerin alone significantly blunted the response (21 +/- 3 to 6 +/- 1 mmHg). Results suggest that a reduction in basal NO release mediates hypoxic fetoplacental vasoconstriction in the perfused human placental cotyledon in vitro.

Ultrasound detection of neural tube defects in patients with elevated maternal serum alpha-fetoprotein.

We conducted this study to determine the accuracy of ultrasound in the prenatal diagnosis of neural tube defects in women with elevated maternal serum alpha-fetoprotein (MSAFP). Among 905 pregnancies, 49 neural tube defects were correctly diagnosed by ultrasound alone; one was not. Ultrasound scanning had 98% sensitivity and 100% specificity for the detection of neural tube defects. The predictive value of a positive ultrasound diagnosis was 100% and of a negative ultrasound 99.9% for neural tube defects. Forty-three other structural abnormalities were also detected in patients with elevated MSAFP, including 19 abdominal wall defects, seven chromosomal abnormalities, five urinary tract abnormalities, one cardiac abnormality, and 11 others. Two chromosomal abnormalities were not detected. We suggest that ultrasound can be used reliably to detect neural tube defects, thereby avoiding the risks of amniocentesis.

Acute hypoxemia does not affect the umbilical artery flow velocity waveform in fetal sheep.

The present study in sheep was undertaken to test whether acute fetal hypoxemia causes abnormalities in the umbilical artery velocity waveform. A 1-hour period of hypoxemia was induced in six chronically catheterized fetal sheep by reducing the inspired oxygen content of the ewe. During hypoxemia, the ratio of the systolic to diastolic velocity did not change significantly compared with controls. From this experimental evidence, we conclude that normal Doppler waveforms in the umbilical artery do not necessarily imply fetal normoxemia in sheep and that, because a direct cause-effect relationship has not been established, fetuses that have abnormal waveforms are not necessarily hypoxemic. Whether this is also true in humans remains to be shown.

Isolation of acylcarnitines from urine: a comparison of methods and application to long-chain acyl-CoA dehydrogenase deficiency.

Carnitine esters from acetylcarnitine (C2 acyl chain) to octadecanoylcarnitine (C18 acyl chain) can be extracted from urine with recoveries of greater than 80%. However, to obtain such recoveries, it is important to choose the method of extraction appropriate to the acylcarnitines of interest. For acylcarnitines with acyl chain length C2 to C8 (acetylcarnitine to octanoylcarnitine), an ion-exchange procedure is recommended. Acylcarnitines with acyl chain length C8 to C12 (octanoylcarnitine to dodecanoylcarnitine) are best isolated from carefully acidified urine by solvent extraction with butan-1-ol. For long-chain acylcarnitines, C10 to C18 (decanoylcarnitine to octadecanoylcarnitine), solvent extraction of unacidified urine with hexan-2-ol is particularly simple and effective.

Calcium mobilization and sensitivity in intact and triton skinned aorta from thyropathologic rats.

Calcium mobilization and sensitivity in aortic rings from hyperthyroid, hypothyroid, and euthyroid rats was examined. The magnitudes of contractions were measured in rings consecutively exposed to phenylephrine (1 microM) incubated in normal physiological saline (PSS), in calcium-free PSS and in normal PSS containing nifedipine (1 microM). By comparing the generated tension under these three conditions it was possible to estimate the contributions of calcium release from the sarcoplasmic reticulum (SR), of influx through voltage gated calcium channels (VGCC), and of influx through receptor operated calcium channels (ROCC). The comparison revealed no change in the contribution of SR calcium release in the three thyroid states, but showed increased VGCC influx and decreased ROCC influx in hyperthyroid rings. No changes were seen in the hypothyroid state. When rings were chemically "skinned" with triton X-100 and subsequently contracted with increasing concentrations of free calcium, dose response curves were not significantly different among rings from the three thyroid states. This suggests that changes in tension development in hyperthyroid aortic tissue may be due, in part, to alterations in membrane calcium influx rather than to SR calcium release or modified calcium activation of contractile elements.

The usefulness of faecal haemoglobin, albumin and alpha-1-antitrypsin in the detection of gastrointestinal bleeding.

A pilot study was undertaken to find out whether faecal haemoglobin, albumin and alpha-1-antitrypsin from patients with gastrointestinal disorders could distinguish active bleeders from non-active bleeders and healthy volunteers. Alpha-1-antitrypsin is not as readily degraded by endogenous and bacterial breakdown as haemoglobin and albumin and consequently could be a better marker for occult bleeding.

Use of Laplace transform analysis to describe the effect of placental embolisation on umbilical arterial Doppler waveforms in fetal sheep.

This is the first study to investigate changes in umbilical arterial Doppler shift waveforms caused by placental embolisation in fetal lambs described by a Laplace transform analysis method. The complete maximum velocity envelope of the waveform was quantified mathematically by the coefficients of the Laplace transform. The changes in the dominant coefficient were significantly correlated with changes in umbilico-placental vascular resistance. The Doppler shift waveforms reproduced those seen clinically in some growth-retarded pregnancies and were acquired in a clinically realistic manner. Increasing vascular resistance two fold in this experiment appeared to produce more consistent changes in the dominant coefficient of the Laplace transform than in the pulsatility index. Both analysis techniques correlated with umbilico-placental vascular resistance and these correlations were not significantly different from each other.

Experimentally induced changes in heart rate alter umbilicoplacental hemodynamics in fetal sheep.

In the anesthetized sheep fetus, we have accelerated heart rate by atrial pacing (n = 6) or caused decelerations by stimulating the vagus nerve (n = 7). Alterations in heart rate were linearly related to changes in the ratio of the diastolic minimum (D) to systolic maximum (S) of flow and velocity, and to changes in the flow pulsatility index in the umbilical artery. Decelerations slightly increased vascular resistance, and decreased blood flow and mean arterial pressure, but accelerations had no significant effect. The index of impedance was unaltered by either intervention. The major factor mediating the influence of heart rate on blood flow pulsatility in the umbilical artery was the aortic blood pressure pulsatility. An equation was derived to adjust flow D/S to a standardized heart rate. Results showed that heart rate correction can affect the interpretation of experimental data.

Effect of placental resistance, arterial diameter, and blood pressure on the uterine arterial velocity waveform: a computer modeling approach.

A computer model was used to simulate velocity waveforms that can be visualized in the human uterine artery using Doppler ultrasound. It was found that increasing uteroplacental vascular resistance from normal caused an increase in the systolic/diastolic velocity ratio (S/D) and pulsatility index (PI) of the waveform. Increasing uteroplacental resistance also caused the appearance of a dicrotic notch. Reducing the uterine artery radius increased the S/D and PI and this effect was accentuated at high placental resistance. In contrast, increasing mean arterial pressure in the uterine artery had little effect on S/D and PI. Results suggest that waveform shape abnormalities observed in obstetric patients with pregnancy-induced hypertension are primarily caused by high uteroplacental vascular resistance and a reduced uterine arterial diameter.

Site-dependent effects of increases in placental vascular resistance on the umbilical arterial velocity waveform in fetal sheep.

Placental vascular resistance was increased by embolization or by arterial vasoconstriction with angiotensin II and the effect on the flow and velocity waveforms in the umbilical artery was examined. Fetal sheep (n = 6) were studied under halothane anesthesia following the implantation of vascular catheters and an umbilical arterial electromagnetic flow probe. Blood flow and velocity (measured using Doppler ultrasound) gradually decreased during diastole and ultimately reversed in direction as cotyledon resistance was increased up to 14 fold. Cotyledon resistance was significantly correlated with the ratio of diastolic to systolic values (D/S ratio) of blood flow (r = -0.94) and velocity (r = -0.79). In contrast, increasing placental resistance up to 16 fold by constricting the umbilical arteries caused no significant change in the shape of the flow or velocity waveform.

Anion-exchange separation techniques with methanol-water solutions of hydrochloric and nitric acids.

Mixed methanol-water systems were shown to be of use in the analysis of samples containing 500-mg amounts of metallic impurities for rare earths and actinides. Detailed study of the hydrochloric acid-methanol system led to improved separation of einsteinium and californium from americium and curium as well as to lanthanideactinide separations. Comparisons of elution orders are also drawn between these systems and the corresponding lithium salt systems, with emphasis on ion-hydration theories.

Fetal blood transfusion.

The concept of transfusing the fetus in utero is simple, but its success demands an experienced, dedicated team, with excellent laboratory back-up. High-resolution ultrasound has enabled us to sample fetal blood. This allows immediate, precise assessment and rational treatment of the anemic fetus, with improved outcome for all such fetuses and, particularly, for the hydropic, moribund group. Fetal blood transfusion programs should be concentrated in regional perinatal centers.

Maternal cigarette smoking: the effects on umbilical and uterine blood flow velocity.

Maternal and fetal effects of smoking one cigarette were assessed in 15 healthy women at 36 to 41 weeks' gestation with no obstetric complications. It was found that smoking was associated with increases in maternal heart rate and blood pressure, but there was no significant change in the uterine artery vascular resistance as measured by means of the systolic/diastolic velocity ratio. There also was an increase in the fetal heart rate as well as a highly significant rise in the systolic/diastolic velocity ratio of the umbilical artery. The responses suggest that smoking causes a direct increase in the vascular resistance of the placenta from the fetal side. This resistance may impair oxygen exchange across the placenta and contribute to the increased perinatal morbidity associated with smoking.

PIP: Maternal cigarette smoking is associated with prematurity, small for gestational age babies, and increased perinatal morbidity and mortality. To study the possible mechanisms involved, 15 women 36-41 weeks pregnant were each given 1 cigarette with a nicotine content of 1.05 mg. Doppler ultrasonography was used to monitor the fetal heart rate, systolic and diastolic pressure in the uterine and umbilical arteries and umbilical and uterine blood velocities. The uterine systolic/diastolic ratio was not significantly elevated, but in the fetus the heart rate was significantly elevated and remained so throughout the study, and the mean umbilical systolic/diastolic ratio was significantly elevated and remained so for 30 minutes. This increased systolic/diastolic ratio in the umbilical artery is similar to that seen in fetuses with intrauterine growth retardation and is indicative of increased vascular resistance of the placenta from the fetal side, which may impair oxygen exchange across the placenta.

Fetal and maternal hemodynamic responses to exercise in pregnancy assessed by Doppler ultrasonography.

It is common for women to undertake vigorous exercise in the late phase of pregnancy. This may have detrimental effects on the blood flow to the uterus and placenta or from the fetus to the placenta. Fifteen pregnant women with no obstetric or medical complications were subjected to a 5-minute exercise period. The maternal heart rate and blood pressure were elevated after exercise. The uteroplacental and umbilical circulations were assessed with Doppler ultrasonography. The ratio of the systolic/diastolic velocity in the uterine artery was elevated, which suggests that uteroplacental vascular resistance increased. The fetal heart rate was elevated after exercise, whereas the systolic/diastolic velocity ratio in the umbilical artery was unaltered. We conclude that moderate maternal exercise causes increased resistance to blood flow in the uterine circulation, whereas the umbilical circulation remains unaltered.

The contractile response of smooth muscle to immersion in hypertonic solutions.

1. Strips of bovine tracheal muscle and rabbit aorta produced sustained contractions on perfusion with Krebs solution made twice normal strength by addition of sucrose. The contractures were relaxed on return to normal Krebs solution. 2. Similar contractures were produced by tracheal muscle strips in Krebs solutions made twice normal strength by addition of galactose, glucose or NaCl whereas urea caused only a transient contraction. 3. In twice normal strength Krebs solution (sucrose added) the basal tension of rat portal vein and guinea-pig taenia coli was increased. Spontaneous mechanical activity was maintained, but the frequency of contractions was reduced. 4. The hypertonic contracture of bovine trachea in twice normal strength Krebs solution (sucrose added) was reduced by 15% by omission of Ca from the bathing fluid (0.1 mmol/l EGTA added). Severe Ca depletion, by prolonged washing in Ca-free Krebs with 12.5 mmol/l EGTA and Carbachol added, resulted in a 77% reduction in the hypertonic contracture. 5. In twice normal Krebs solution (sucrose added), the hypertonic contracture was partially relaxed by isoprenaline (4 x 10(-6) mol/l); the contractile response to carbachol was reduced; the contractile response to high-K Krebs solution was maintained. 6. Atropine (5 x 10(-7) mol/l) abolished the contractile response to carbachol, but had no effect on the hypertonic contracture. 7. It is suggested that the contraction of bovine tracheal strips in hypertonic solutions is mainly due to activation of the contractile myofilaments rather than simple cell shrinkage. Hypertonic solutions may also interfere with some steps in the excitation-contraction coupling sequence.

Vascular responsiveness in the unstressed borderline hypertensive rat.

This study compares vascular responses of unstressed borderline hypertensive rats (BHR) to age-matched Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Rings of thoracic aorta were mounted for isometric force determinations in tissue baths. Cumulative additions of phenylephrine (PE) or serotonin (5-HT) produced contractile responses in BHR aorta that were less than WKY but greater than SHR. Removing the endothelium increased force development to both agonists, with BHR showing the greatest increase. Based on EC50 determinations, no differences in PE sensitivity existed between groups, although in response to 5-HT, rings from SHR were significantly more sensitive than WKY. While the sensitivity of all rings increased with denuding, BHR showed a greater relative increase in sensitivity than WKY or SHR (intact EC50 divided by denuded EC50) to both PE and 5-HT. This suggests that there may be greater endothelium-derived relaxation in BHR than in WKY or SHR. In rings precontracted with 1 microM PE, the cumulative addition of acetylcholine resulted in greater relaxation in BHR than in SHR and WKY preparations. Thus, rings from unstressed BHR, which have only slightly higher blood pressures than WKY rats, demonstrate greater endothelium-mediated relaxation than WKY or SHR. Increased endothelium-derived relaxation may represent a possible mechanism for masking hypertension in BHR that is compromised as a result of exposure to a chronic stress paradigm.