The effect of magnesium sulfate tocolysis on the fetal biophysical profile

The role of the fetal biophysical profile in the management of fetal growth restriction

Growth-restricted fetuses are at risk of hypoxemia, acidemia, and stillbirth because of progressive placental dysfunction. Current fetal well-being, neonatal risks following delivery, and the anticipated rate of fetal deterioration are the major management considerations in fetal growth restriction. Surveillance has to quantify the fetal risks accurately to determine the delivery threshold and identify the testing frequency most likely to capture future deterioration and prevent stillbirth. From the second trimester onward, the biophysical profile score correlates over 90% with the current fetal pH, and a normal score predicts a pH >7.25 with a 100% positive predictive value; an abnormal score on the other hand predicts current fetal acidemia with similar certainty. Between 30% and 70% of growth-restricted fetuses with a nonreactive heart rate require biophysical profile scoring to verify fetal well-being, and an abnormal score in 8% to 27% identifies the need for delivery, which is not suspected by Doppler findings. Future fetal well-being is not predicted by the biophysical profile score, which emphasizes the importance of umbilical artery Doppler and amniotic fluid volume to determine surveillance frequency. Studies with integrated surveillance strategies that combine frequent heart rate monitoring with biophysical profile scoring and Doppler report better outcomes and stillbirth rates of between 0% and 4%, compared with those between 8% and 11% with empirically determined surveillance frequency. The variations in clinical behavior and management challenges across gestational age are better addressed when biophysical profile scoring is integrated into the surveillance of fetal growth restriction. This review aims to provide guidance on biophysical profile scoring in the in- and outpatient management of fetal growth restriction.

A Review on the Vagus Nerve and Autonomic Nervous System During Fetal Development: Searching for Critical Windows

The autonomic nervous system (ANS) is one of the main biological systems that regulates the body's physiology. Autonomic nervous system regulatory capacity begins before birth as the sympathetic and parasympathetic activity contributes significantly to the fetus' development. In particular, several studies have shown how vagus nerve is involved in many vital processes during fetal, perinatal, and postnatal life: from the regulation of inflammation through the anti-inflammatory cholinergic pathway, which may affect the functioning of each organ, to the production of hormones involved in bioenergetic metabolism. In addition, the vagus nerve has been recognized as the primary afferent pathway capable of transmitting information to the brain from every organ of the body. Therefore, this hypothesis paper aims to review the development of ANS during fetal and perinatal life, focusing particularly on the vagus nerve, to identify possible "critical windows" that could impact its maturation. These "critical windows" could help clinicians know when to monitor fetuses to effectively assess the developmental status of both ANS and specifically the vagus nerve. In addition, this paper will focus on which factors-i.e., fetal characteristics and behaviors, maternal lifestyle and pathologies, placental health and dysfunction, labor, incubator conditions, and drug exposure-may have an impact on the development of the vagus during the above-mentioned "critical window" and how. This analysis could help clinicians and stakeholders define precise guidelines for improving the management of fetuses and newborns, particularly to reduce the potential adverse environmental impacts on ANS development that may lead to persistent long-term consequences. Since the development of ANS and the vagus influence have been shown to be reflected in cardiac variability, this paper will rely in particular on studies using fetal heart rate variability (fHRV) to monitor the continued growth and health of both animal and human fetuses. In fact, fHRV is a non-invasive marker whose changes have been associated with ANS development, vagal modulation, systemic and neurological inflammatory reactions, and even fetal distress during labor.

Effect of magnesium sulfate on fetal heart rate patterns in the second stage of labor

OBJECTIVE

To estimate the effect of maternal exposure to magnesium sulfate on fetal heart rate characteristics during active labor.

METHODS

Within a 4-year retrospective cohort study of consecutive term deliveries reaching the second stage of labor, we compared women exposed to magnesium for severe preeclampsia to all women not exposed. Primary outcome was the electronic fetal monitoring tracing in the 30 minutes preceding delivery. Secondary outcomes were fetal acidemia and nursery disposition. Attributable risk estimates and multivariable logistic regression were used to estimate the association between magnesium exposure and fetal heart rate characteristics. Unadjusted risk estimates for the association between fetal heart rate characteristics and neonatal outcomes were generated stratified by group.

RESULTS

Of 5,387 women, 248 (4.6%) were exposed to magnesium. Magnesium exposure was associated with lower fetal heart rate baseline (136.9 ± 12.3 beats per minute compared with 139.0 ± 13.5 beats per minute; P=.02), increased risk of baseline less than 120 beats per minute (adjusted odds ratio [OR] 1.76, 95% confidence interval [CI] 1.21-2.56), and increased risk of absent or minimal variability (adjusted OR 2.41, 95% CI 1.78-3.27). More than 20% increased frequency of ever absent or minimal variability was attributable to magnesium (attributable risk 0.21, 95% CI 0.15-0.27). There were no significant differences in presence or number of accelerations or decelerations; however, magnesium was associated with fewer prolonged decelerations (adjusted OR 0.64, 95% CI 0.49-0.84). After excluding women with adverse neonatal outcomes, these associations remained.

CONCLUSION

Maternal exposure to magnesium is associated with lower fetal heart rate baseline within the accepted normal range, decreased variability, and fewer prolonged decelerations without evidence of adverse effect on neonatal outcome.

LEVEL OF EVIDENCE

II.

The uses and limitations of the fetal biophysical profile

In the second half of the twentieth century, true antepartum fetal assessment became possible, mainly due to the advent of real-time ultrasound. Initially, the most widely used form of antepartum fetal assessment was electronic fetal heart rate monitoring, through the nonstress test or the oxytocin-induced contraction stress test. It was soon realized, however, that these forms of monitoring had significant limitations. The biophysical profile allows a more thorough evaluation of fetal well-being and has the potential to significantly reduce the false-positive rate of the nonstress test/contraction stress test.

Biophysical profile for fetal assessment in high risk pregnancies

BACKGROUND

A biophysical profile (BPP) includes ultrasound monitoring of fetal movements, fetal tone and fetal breathing, ultrasound assessment of liquor volume with or without assessment of the fetal heart rate. The BPP is performed in an effort to identify babies that may be at risk of poor pregnancy outcome, so that additional assessments of wellbeing may be performed, or labour may be induced or a caesarean section performed to expedite birth.

OBJECTIVES

To assess the effects of the BPP when compared with conventional monitoring (CTG only or MBPP) on pregnancy outcome in high-risk pregnancies.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (October 2007), CENTRAL (The Cochrane Library 2006, Issue 4), MEDLINE (1966 to November 2006), EMBASE (1974 to November 2006) and CINAHL (1980 to November 2006).

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials involving a comparison of fetal BPP with other forms of antepartum fetal assessment in women with high-risk pregnancies.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed eligibility, quality and extracted data.

MAIN RESULTS

We included five trials, involving 2974 women. Most trials were not of high quality. Although the overall incidence of adverse outcomes was low, available evidence from randomised controlled trials does not support the use of BPP as a test of fetal wellbeing in high-risk pregnancies. We found no significant differences between the groups in perinatal deaths (relative risk (RR) 1.33, 95% confidence interval (CI) 0.60 to 2.98) or in Apgar score less than seven at five minutes (RR 1.27, 95% CI 0.85 to 1.92). Combined data from the two high-quality trials suggest an increased risk of caesarean section in the BPP group RR 1.60, 95% CI 1.05 to 2.44, n = 280, interaction test P = 0.03. However, the number of participating women was relatively small (n = 280). Therefore, additional evidence is required in order to be definitive regarding the efficacy of this test in high-risk pregnancies. Furthermore, the impact of the BPP on other interventions, length of hospitalisation, serious short-term and long-term neonatal morbidity and parental satisfaction requires further evaluation.

AUTHORS' CONCLUSIONS

At present, there is insufficient evidence from randomised trials to support the use of BPP as a test of fetal wellbeing in high-risk pregnancies.

Magnesium Sulfate: The First-Line Tocolytic

Magnesium sulfate has become the first-line tocolytic for short-term use to arrest idiopathic preterm labor. The reasons for its acceptance include familiarity of the drug, ease of use, and the virtual absence of serious maternal side effects. Sufficient data exist showing its efficacy if used in higher doses. Attention to treating preterm labor has shifted to seeking answers about the fundamental causes. Gathering information about the specific causes and designing tailor-made treatment protocols for each of the numerous potential causes is essential. Scientifically sound research is needed to obtain answers about the important clinical questions surrounding magnesium sulfate.

The Effect of Magnesium Sulfate on the Behavioral Activities of Fetal Goats

OBJECTIVES

To investigate fetal heart rate accelerations, fetal breathing movements, and fetal electrocortical activities during administration of magnesium sulfate to fetal goats.

METHODS

The fetal heart rate accelerations, fetal breathing movements, and fetal electrocortical activities during 6 hours of continuous magnesium sulfate infusion into the fetal jugular vein were examined in 8 chronically instrumented fetal goats at 124-131 days of gestation. Fetal breathing movements were defined as repetitive negative fluctuations of the fetal tracheal pressure. Fetal electrocortical activities were assessed by visual analysis of periods of high-voltage and low-voltage electrocortical activities.

RESULTS

Continuous infusion of magnesium sulfate for 6 hours significantly increased the fetal plasma magnesium concentration from 2.8 +/- 1.2 to 8.3 +/- 2.6 mg/dL without significant changes in fetal arterial blood gases. The incidence of fetal heart rate accelerations during magnesium infusion was significantly decreased from that found during the control periods. After 2 hours of infusion, the incidence of fetal breathing movements significantly decreased from 33.9% +/- 20.5% to 1.2% +/- 1.4% and remained at this level during the remaining 4 hours of magnesium infusion. The percentage of time that the fetuses were found to have low-voltage electrocortical activities decreased from 51.6% +/- 9.0% to 40.4% +/- 8.2% after 2 hours of infusion but recovered to 49.9% +/- 12.0% by 6 hours of magnesium infusion.

CONCLUSION

We concluded that fetal magnesium sulfate administration affected fetal heart rate accelerations and fetal breathing movements continuously but electrocortical activities only temporarily during 6 hours of observations.

An update on the controversies of tocolytic therapy for the prevention of preterm birth

Preterm birth is the major cause of perinatal mortality and morbidity in the developed world. Where there are no contraindications to their use, tocolytics can improve neonatal survival rates by approximately 3% per day between 23 and 27 weeks gestation with a concomitant reduction in morbidity. The ultimate aim of tocolytic therapy is to prolong pregnancy until growth and maturation is complete, but even short-term delay may enable the administration of antepartum glucocorticoids to reduce hyaline membrane disease or to arrange transfer to a center with neonatal intensive care facilities. Both of these have been shown to reduce neonatal mortality and morbidity. Until recently, none of the currently used tocolytics, whether licensed or unlicensed, were developed specifically for the inhibition of preterm labor and consequently, they exhibit various potentially serious side-effects. As a result of the recent licensing of the oxytocin antagonist, atosiban, developed for the treatment of preterm labor and due to its high utero-specificity, obstetricians have experienced an advance in their options for the management of spontaneous preterm labor.

Magnesium sulfate as a tocolytic agent

Although magnesium sulfate is widely used as a tocolytic agent in the hope of preventing spontaneous preterm birth, there is a paucity of data from large well-designed randomized clinical studies demonstrating the efficacy of magnesium sulfate therapy. Given the potential for untoward side effects and the inherent risks of magnesium sulfate therapy, a thorough understanding of the potential risks and benefits of this agent is needed. To accomplish this understanding we have provided a detailed review the history, pharmacology, physiology, maternal/fetal side effects, and tocolytic efficacy of magnesium sulfate.

Fetal cardiovascular function during prolonged magnesium sulfate tocolysis

The purpose of this study was to evaluate the fetal cardiovascular function during prolonged magnesium sulfate tocolysis. We performed a fetal ultrasonographic examination in 15 patients (Mg group) during magnesium sulfate tocolysis for the treatment of preterm labor. The maternal serum magnesium concentration was 5.7 +/- 0.5 mg/dl at the time of the examination. Sixteen fetuses in normal pregnancies at similar gestational ages were used as the control group. The fetal heart rate and the middle cerebral artery pulsatility index in the Mg group were lower than in the control group (p < 0.01). Fractional shortening (FS) of the right ventricle in the Mg group was lower (p < 0.01), while FS of the left ventricle was higher (p < 0.01) than in the controls. The calculated blood flow through the tricuspid orifice in the Mg group was lower than in the control group (p < 0.01). In contrast, the blood flow through the mitral orifice in the Mg group was higher than in the control group (p < 0.01). In conclusion, in spite of the fact that the right ventricular function is depressed, the fetus maintains its cardiac output during prolonged hypermagnesemia by increasing its left ventricular function. These results indicate the different fetal intracardiac and peripheral circulation, especially in the brain, from normal fetuses.

Effect of antenatal steroid administration on the fetal biophysical profile

PURPOSE

Our objective was to determine whether antenatal steroid administration affects the biophysical profile score in fetuses.

METHODS

A prospective study was conducted in 84 fetuses between 28 and 34 weeks' menstrual age at risk of preterm delivery. Two intramuscular injections of 12 mg of betamethasone were given to the mother 24 hours apart. All fetuses underwent biophysical profile testing prior to and between 24 and 48 hours after steroid administration. Biophysical profiles (including nonstress tests) were evaluated by two maternal-fetal medicine specialists blinded to the timing of steroid administration. Neonatal outcome, including Apgar score, menstrual age at delivery, admission to and length of stay in the neonatal intensive care unit, and mortality, was analyzed in all subjects.

RESULTS

In 31 (37%; 95 confidence interval, 26.6-47.2%) of 84 cases, the biophysical profile score decreased at least 2 points after steroid administration. The most commonly affected variables were fetal breathing and the nonstress test. There was no significant difference in the neonatal outcome between the fetuses whose biophysical profile decreased and those whose did not.

CONCLUSIONS

Biophysical profile scores were decreased in more than one third of fetuses within 48 hours of antenatal steroid administration, but neonatal outcome was not affected. Knowledge of this occurrence could avoid incorrect decision making regarding fetal well-being.

Intrapartum fetal distress and magnesium sulfate

OBJECTIVE

Intrapartum fetal distress is an obstetric emergency traditionally managed by immediate delivery by either the vaginal route or cesarean section. However, there is usually time to attempt intrauterine resuscitation. The purpose of this study was to report the utilization of magnesium sulfate for intrauterine resuscitation.

METHOD

Twenty-one fetuses received magnesium sulfate 4-g intravenous bolus in mothers awaiting cesarean section for fetal distress in the labor room of the Complejo Hospitalario Metropolitano de la Caja de Seguro Social de Panamá, from March through August 1997. Fetal distress in labor was defined as the presence of repetitive late decelerations, persistent loss of baseline variability, severe variable decelerations, or bradycardia.

RESULTS

Twenty-one fetuses received magnesium sulfate 4-g intravenous bolus in mothers awaiting cesarean section for fetal distress. Uterine activity ceased in seven patients, diminished in 13 patients and did not change in one. In all cases, but one, there was recovery of the FHR within 4 min; furthermore there was rose reactive of FHR in nine patients. The 1-min Apgar scores were 7 or above in 18 cases and the 5-min Apgar scores were 7 or above in 20 patients.

CONCLUSIONS

In summary, magnesium sulfate may be useful in the management of acute intrapartum fetal distress when there is evidence of increased uterine activity.

The effect of magnesium sulfate on fetal heart rate parameters: A randomized, placebo-controlled trial

OBJECTIVE

We sought to determine the effect of magnesium sulfate on fetal heart rate baseline value, variability, and acceleration-deceleration pattern.

STUDY DESIGN

Normal, nonlaboring pregnant patients at >30 weeks' gestation were recruited. Baseline fetal heart rate monitoring for 1 hour was performed. After an 800-kcal meal, patients were randomized to receive either an intravenous loading dose of 6 g of magnesium sulfate in 100 mL of isotonic sodium chloride solution or 100 mL of isotonic sodium chloride solution alone. Subsequently, patients in the magnesium sulfate group received a 2-g/h intravenous infusion for 3 hours at a rate of 125 mL/h. Patients randomized to the sodium chloride solution group received a sodium chloride solution infusion at a similar rate (unlabeled intravenous bags). Maternal blood was drawn at 0, 1, and 3 hours for determination of total and ionized magnesium and calcium, electrolyte, and glucose levels. One hour of fetal heart rate monitoring was repeated at 1 and 3 hours of infusion. Tracings were interpreted without identifiers (of time or group) by using the National Institute of Child Health and Human Development fetal heart rate monitoring guidelines.

RESULTS

Magnesium sulfate administration resulted in decreased fetal heart rate baseline values and variability in the third hour. The fetal heart rate baseline value was 134.4 +/- 6.3 versus 136.6 +/- 6.4 beats/min before infusion (P >.05), 134.4 +/- 7.1 versus 135.1 +/- 6. 6 beats/min in the first hour (P >.05), and 134.6 +/- 7.1 versus 132. 3 +/- 7.6 beats/min in the third hour (P <.05) in the sodium chloride solution group versus the magnesium sulfate group, respectively. Fetal heart rate variability (grades 1-5) was 2.75 +/- 0.33 versus 2.82 +/- 0.29 before infusion (P >.05), 2.81 +/- 0.30 versus 2.84 +/- 0.28 in the first hour (P >.05), and 2.71 +/- 0.52 versus 2.67 +/- 0.36 in the third hour in the sodium chloride solution group versus the magnesium sulfate group, respectively (P <. 05). Magnesium sulfate blocked the positive correlation between gestational age and number of accelerations found in control subjects. No significant decelerations were identified.

CONCLUSIONS

Prolonged administration of magnesium sulfate was associated with decreased fetal heart rate baseline values and variability. Given the small magnitude of these changes, the clinical significance of these findings is questionable. Magnesium sulfate inhibition of the increasing number of accelerations with gestational age needs to be considered when fetal well-being is assessed.

Failure of magnesium sulfate infusion to inhibit uterine activity in pregnant sheep

OBJECTIVES

Our purpose was to determine the effect of magnesium sulfate infusion on nonlabor uterine contractures and corticotropin-induced preterm uterine contractions in pregnant sheep.

STUDY DESIGN

Fetal and maternal vascular catheters and uterine electromyographic electrodes were surgically placed in 15 pregnant sheep between 118 and 125 days' gestation. After 3 to 5 days of recovery, magnesium sulfate was infused into 7 ewes with a 0.11 gm/kg bolus over 20 minutes, followed by 0.08 gm/kg/hr. In 8 animals labor was induced with use of an intrafetal corticotropin infusion, after which 4 ewes received magnesium sulfate and 4 received saline solution. Continuous recordings of uterine electromyographic activity, amniotic pressure, fetal heart rate, blood pressure, and tracheal pressure were made. Maternal and fetal magnesium, calcium, albumin concentrations, and blood gases were determined before and during the infusion.

RESULTS

Maternal magnesium concentrations increased from an average of 0.94 +/- 0.03 mmol/L to 2.73 +/- 0.1 mmol/L at the end of the bolus, remaining elevated (2.44 +/- 0.17 mmol/L) for 8 hours. Fetal magnesium concentrations (0.89 +/- 0.03 mmol/L before the bolus) did not change with the maternal infusion. In ewes not in labor, uterine contractures occurred 3.7 +/- 0.7 times per 2 hours before and did not change significantly with the infusion of magnesium sulfate. During corticotropin-induced preterm labor uterine contractions were present 13 +/- 3.2 times per hour before infusions and were unchanged by infusion of magnesium sulfate to the ewes.

CONCLUSIONS

Magnesium sulfate infusion in pregnant sheep has no effect on either nonlabor uterine contractures or on corticotropin-induced preterm uterine contractions.

Effect of intravenous magnesium sulfate on the biophysical profile of the healthy preterm fetus

OBJECTIVE

The null hypothesis is that intravenous magnesium sulfate does not affect the biophysical profile of the healthy preterm fetus.

STUDY DESIGN

Thirty-one fetuses of 25 patients between the gestational ages of 24 and 35 weeks, median 31.4 and mean (+/- SD) 30.4 (+/- 2.9), who required tocolysis for uterine contractions were prospectively studied. After normal fetal biophysical assessment was documented, intravenous magnesium sulfate was started as a 4 or 6 gm loading dose and then infused at 2 to 3.5 gm/hr to achieve tocolysis. Blood was drawn for measurement of maternal serum magnesium levels immediately before intravenous magnesium sulfate was administered and at 2 and 12 hours after the loading dose. Biophysical profiles, consisting of a possible 12 points, were performed at the same time as blood was drawn. Serum magnesium levels were compared with one-way analysis of variance for repeated measures and biophysical profile scores with Friedman's test. Statistical significance was considered p < 0.05.

RESULTS

Mean (+/- SD) serum magnesium levels were 1.7 (+/- 0.1) mg/dl before infusion, 4.3 (+/- 0.6) mg/dl at 2 hours, and 5.2 (+/- 0.7) mg/dl at 12 hours (p < 0.001). Six fetuses did not have a 12-hour biophysical profile; three were delivered for severe variable decelerations, two progressed in labor, and in one tocolysis was discontinued. The median biophysical profile score was 11 before intravenous magnesium sulfate, at 2 hours, and at 12 hours after the loading dose. The biophysical parameters present and the percentage of fetuses with each parameter were as follows: breathing (> 30 seconds), 88% (22/25) before magnesium sulfate, 84% (21/25) at 2 hours, and 92% (23/25) at 12 hours; nonstress test (reactive), 84% (21/25) before magnesium sulfate, 68% (17/25) at 2 hours, and 80% (20/25) at 12 hours; movement (normal), 100% (25/25) before magnesium sulfate, 100% (25/25) at 2 hours, and 96% (24/25) at 12 hours.

CONCLUSION

Intravenous magnesium sulfate did not significantly alter the biophysical profile in the 25 fetuses evaluated by three biophysical profiles in spite of the significant increase in maternal serum magnesium levels.

Transfer of maternally administered magnesium sulfate into the fetal compartment of the rat: assessment of amniotic fluid, blood, and brain concentrations

OBJECTIVE

Our purpose was to determine whether parenteral magnesium sulfate crosses the rat placenta and enters the fetal brain.

STUDY DESIGN

Twenty-eight pregnant female Long-Evans rats were divided into four groups, seven animals in each group. These groups included the following: single saline solution injection group evaluated after 20 minutes (control), single magnesium sulfate injection (270 mg/kg) evaluated after 20 minutes, and prolonged (2 and 4 hours) serum magnesium elevation (270 mg/kg loading and then 27 mg/kg every 20 minutes for maintenance). Each animal was killed, and maternal and fetal sera, amniotic fluid, and specific brain areas were analyzed for levels of magnesium. Statistical analysis included analysis of variance, multiple comparison procedure, and linear regression analysis.

RESULTS

All three regimens of maternal subcutaneous magnesium sulfate resulted in significantly elevated maternal serum magnesium concentrations (p < 0.01). Fetal blood magnesium concentration rose from 3.9 +/- 0.3 to 4.9 +/- 0.1 mg/dl after 2 hours of continuous injections (p < 0.05), and to 5.3 +/- 0.0 mg/dl after 4 hours (p < 0.01). Amniotic fluid magnesium concentrations rose from 4.2 +/- 0.2 to 5.1 +/- 0.1 mg/dl after 4 hours (p < 0.05). Maternal blood magnesium concentrations were significantly correlated with amniotic fluid concentrations (r = 0.59, p < 0.01). Four hours of maternal magnesium sulfate treatment resulted in a 25% increase in magnesium concentrations in the fetal forebrain (38.3 +/- 2.3 to 47.9 +/- 3.5 mg/dl/gm, p < 0.05). No significant changes in magnesium concentrations were detected in hindbrain.

CONCLUSION

Magnesium sulfate injected subcutaneously into rats crosses the placenta within 2 hours of sustained magnesium levels, enter the fetal blood-brain barrier, and concentrates in the forebrain.

Nickel-induced increases in gap junctional communication in the uterine cell line SK-UT-1

Previous studies have suggested that gap junctions may have a role in various uterine functions, including parturition. Because nickel has been demonstrated to increase uterine contractility in vitro, the effect of nickel (II) chloride on gap junctional communication was assessed in a tumorigenic uterine cell line, SK-UT-1 (ATCC HTB 114). Cells were exposed in vitro to 25 and 50 microM NiCl2 for 24 h or 100 microM NiCl2 for 3, 12, and 24 h, then functional gap junctional communication was measured as the transfer of Lucifer yellow dye from microinjected donor cells to their primary neighbor cells. Dye transfer was significantly increased only in cell cultures exposed to 100 microM NiCl2 for 24 h, compared to untreated controls, lower doses, and shorter exposure periods. This response was inhibited by the simultaneous co-treatment of SK-UT-1 cells with magnesium by adding 100 microM MgSO4 to the dosing medium. Possible mechanisms and implications for these findings are discussed.