Neuronal death after perinatal asphyxia

Chronic allopurinol treatment during the last trimester of pregnancy in sows: effects on low and normal birth weight offspring

Low-birth-weight (LBW) children are born with several risk factors for disease, morbidity and neonatal mortality, even if carried to term. Placental insufficiency leading to hypoxemia and reduced nutritional supply is the main cause for LBW. Brain damage and poor neurological outcome can be the consequence. LBW after being carried to term gives better chances for survival, but these children are still at risk for poor health and the development of cognitive impairments. Preventive therapies are not yet available. We studied the risk/efficacy of chronic prenatal treatment with the anti-oxidative drug allopurinol, as putative preventive treatment in piglets. LBW piglets served as a natural model for LBW. A cognitive holeboard test was applied to study the learning and memory abilities of these allopurinol treated piglets after weaning. Preliminary analysis of the plasma concentrations in sows and their piglets suggested that a daily dose of 15 mg.kg(-1) resulted in effective plasma concentration of allopurinol in piglets. No adverse effects of chronic allopurinol treatment were found on farrowing, birth weight, open field behavior, learning abilities, relative brain, hippocampus and spleen weights. LBW piglets showed increased anxiety levels in an open field test, but cognitive performance was not affected by allopurinol treatment. LBW animals treated with allopurinol showed the largest postnatal compensatory body weight gain. In contrast to a previous study, no differences in learning abilities were found between LBW and normal-birth-weight piglets. This discrepancy might be attributable to experimental differences. Our results indicate that chronic prenatal allopurinol treatment during the third trimester of pregnancy is safe, as no adverse side effects were observed. Compensatory weight gain of treated piglets is a positive indication for the chronic prenatal use of allopurinol in these animals. Further studies are needed to assess the possible preventive effects of allopurinol on brain functions in LBW piglets.

Magnesium sulfate effect on erythrocyte membranes of asphyxiated newborns

OBJECTIVES

Magnesium sulfate has been recognized as a neuroprotective agent against hypoxia-ischemia, mainly by the protection from the excitotoxicity associated with increased glutamate concentration. However, the mechanism of MgSO4 action is not fully understood and is considerably controversial.

DESIGN AND METHODS

During the 2 first hours of life, the asphyxiated full-term newborns were treated intravenously with one dose of MgSO4 250 mg/kg body weight. At birth, after 6 and 48 h of life the activity of ATP-dependent enzymes in erythrocyte membranes: Mg2+-ATPase, Ca2+-ATPase, protein kinases A and C, were determined. Using monoclonal antibodies, the band 3 and its phosphotyrosine level were also assayed.

RESULTS

The time-dependent decrease of Ca2+-ATPase activity was detected in untreated newborns, whereas MgSO4 prevented this reduction. After 48 h, protein kinases activities differed in MgSO4-treated and untreated groups. Magnesium therapy increased the amount of band 3 and diminished proteolytic degradation of this protein.

CONCLUSION

Our results demonstrated, for the first time, that magnesium sulfate treatment significantly altered the activities of some important enzymes in erythrocyte membrane from asphyxiated newborns. It also reduced the post-asphyxial damages of membrane compounds. These data may partly explain the molecular mechanisms of MgSO4 action in asphyxiated newborns.

Protein kinases activities in erythrocyte membranes of asphyxiated newborns

OBJECTIVES

Perinatal asphyxia represents a major cause of acute brain impairment and mortality in neonates. To develop the effective therapies able to reduce post-asphyxial damages, the understanding of biochemical processes accompanying asphyxia appears to be of the great relevance.

DESIGN AND METHODS

The activities of protein kinases A and C, and tyrosine kinases in erythrocyte membranes of healthy and asphyxiated neonatals were compared. Using monoclonal antibodies the band 3 presence and its phosphotyrosine levels were assayed.

RESULTS

In asphyxiated erythrocyte membranes the activities of PKA and tyrosine kinases increased, whereas the activity of PKC was reduced in relation to healthy newborns. Under asphyxia the band 3 has been overphosphorylated; however, its amount decreased.

CONCLUSION

These findings may provide some evidence for a potential role of asphyxia in disturbance of phosphorylation processes in erythrocytes, as reflected by altered protein kinases activities. The diminished band 3 presence may be partially responsible for the impairment of erythrocyte function.

The physiology of fetal heart rate patterns and perinatal asphyxia

The purpose of electronic fetal heart rate (FHR) monitoring is the ongoing assessment of fetal oxygenation. FHR tracings are analyzed for characteristic patterns that signify specific hypoxic or nonhypoxic events. A working knowledge of fetal physiology and the fetal response to hypoxia can aid and refine clinical interpretation of FHR patterns during labor. This article reviews the fetal response to decreased oxygenation, the physiology of subsequent FHR patterns and the clinical presentation of asphyxia in the newborn.

Determination of the spatial distribution of major elements in the rat brain with X-ray fluorescence analysis

An energy dispersive X-ray fluorescence analysis was applied for determining the spatial (two-dimensional) distribution of elemental concentrations in rat brain sections. Freeze-dried brain sections prepared from normal and ischemic rats with middle cerebral artery occlusion were scanned with a collimated X-ray beam (0.18 mm in diameter, 50-kV acceleration voltage). The fluorescent Kalpha X-rays of P, S, Cl, and K were detectable, so that the two-dimensional distribution of fluorescent X-ray intensities could be determined for these elements. Furthermore, quantitative determination was possible for P and K by using the fundamental parameter technique. However, the accurate determination of Na and Ca was difficult, because of the low energy of Kalpha X-ray of Na, and the interference of K-Kbeta with Ca-Kalpha. The change in elemental concentrations in ischemic tissue, including the decrease in K concentration and increase in Cl concentration, was demonstrated by this method as a two-dimensional contour map. Since it is possible to obtain a pictorial representation of the elemental concentration in tissue sections, this method may be useful to evaluate the ionic changes in injured brain tissue in relation to histological or autoradiographical observations.

Absence of neuronal damage after umbilical cord occlusion of 10, 15, and 20 minutes in midgestation fetal sheep

OBJECTIVES

Our purpose was to determine whether neuronal damage results after total umbilical cord occlusion of increasing duration in midgestation fetal sheep.

STUDY DESIGN

We performed total umbilical cord occlusion during 10 (n = 11), 15 (n = 8), or 20 (n = 4) minutes in chronically instrumented midgestation fetal sheep. Nine fetuses served as sham controls. During the experiment fetal blood pressure (mean arterial pressure) and heart rate were continuously recorded. Fetal blood gas analyses were performed at regular intervals before, during, and after the occlusion. Three days after the occlusion neuronal damage was evaluated histologically in three regions of the fetal brain.

RESULTS

Total umbilical cord occlusion resulted in hypotension, bradycardia, severe mixed acidemia, hypoxia, and hypercapnia. All fetuses survived the occlusion. No neuronal damage nor macroscopic intraventricular or germinal matrix hemorrhages were observed in either group.

CONCLUSION

Prolonging the duration of total umbilical cord occlusion in midgestation fetal sheep resulted in a progressive increase in the severity of asphyxia, not in neuronal damage.

Magnesium sulfate therapy during asphyxia in near-term fetal lambs does not compromise the fetus but does not reduce cerebral injury

OBJECTIVE

Our purpose was to investigate (1) the safety of fetal magnesium sulfate treatment and (2) possible beneficial effects on the brain during perinatal asphyxia.

STUDY DESIGN

In 20 chronically instrumented fetal lambs (gestational age 125.8 +/- 3.5 days) four total umbilical cord occlusions for 5 minutes were repeated at 30-minute intervals. Fetuses received either saline solution (n = 11) or magnesium sulfate (n = 9) as a bolus of 300 mg intravenously 2 hours before occlusions, followed by an infusion of 100 mg/hr until 1 hour after occlusions.

RESULTS

In the treated fetuses plasma magnesium levels rose from 0.85 +/- 0.20 to 2.23 +/- 0.40 mmol/ L. Occlusions induced asphyxia, associated with mortality; 4 of 11 fetuses in the control group versus 1 of 9 in the magnesium-treated group died (not significant). Fetal electroencephalographic activity decreased and cerebral impedance increased during occlusions. Maximum spike and seizure activity occurred 5 to 10 hours after asphyxia. Neuronal loss was primarily localized in the corpus striatum. Magnesium caused no alterations in blood pressure, heart rate, or cerebral and peripheral blood flow, nor did it influence electrophysiologic responses or neuronal loss.

CONCLUSIONS

Administration of magnesium sulfate was safe but did not offer significant cerebral protection from asphyxia in the near-term fetal lamb.

Brief repeated umbilical cord occlusions cause sustained cytotoxic cerebral edema and focal infarcts in near-term fetal lambs

The aim of this study was to determine whether asphyxia induced by clinically relevant, brief repetitive umbilical cord occlusions is associated with cerebral compromise. Chronically instrumented fetal lambs were studied at 126.5 +/- 2.8 d of gestation (mean +/- SD, term 147 d). Occlusions were performed 1 out of every 2.5 min (group I, n = 7), 2 out of every 5 min (group II, n = 9), or not at all (shams, group III, n = 5), and discontinued at a predetermined threshold of severe or persistent hypotension. After 58 +/- 8 and 24 +/- 2 occlusions, in groups I and II, respectively, the pH was 6.83 +/- 0.09, Pco2 9.52 +/- 1.4 kPa, base excess -23.5 +/- 3.7 mM, and lactate 14.1 +/- 1.6 mM. Two fetuses (out of group II) did not recover from the final occlusion. Ongoing asphyxia was associated with progressive suppression of the EEG, which occurred faster and with more epileptiform and spike activity in group II. Cortical impedance remained elevated for 15.0 +/- 4.0 and 11.5 +/- 4.4 h, for groups I and II, respectively (NS). Focal infarcts occurred in the parasagittal cortex, thalamus, and cerebellum, in 6 out of 14 surviving asphyxiated fetuses. Mild selective neuronal loss was observed in these regions in 13 out of 14 fetuses. Infarction was associated with a longer period of blood pressure below baseline levels, with more epileptiform activity, and with slower normalization of the EEG. In a paradigm mimicking birth asphyxia, histologic damage similar to that observed clinically was found. The results suggest that brief repeated insults interact, leading to cardiac compromise and cumulative cell membrane damage in the fetal cerebrum.