Cerebral metabolism during sustained hypoxemia in preterm fetal sheep

OBJECTIVE

The purpose of this study was to determine the effect of sustained hypoxia with resulting metabolic acidosis on cerebral metabolism in the preterm ovine fetus.

STUDY DESIGN

Twelve fetal sheep were studied at 0.75 of gestation during a normoxic control period, after 1 and 8 hours of sustained hypoxemia, and again after a 1-hour recovery period. Cerebral arteriovenous differences were analyzed for oxygen content, blood gases and pH, glucose, and lactate. Cerebral blood flow was measured with the microsphere technique.

RESULTS

Induced hypoxemia resulted in a variable degree of fetal acidemia that was entirely metabolic. Although cerebral oxidative metabolism was well maintained throughout the study, cerebral glucose consumption was variably increased when measured after 1 hour of sustained hypoxemia, with a subsequent decrease after 1 hour of recovery. Although lactate was neither consumed nor produced during the control period, by 8 hours of hypoxic study a significant efflux of lactate from the brain was evident, which continued into the recovery period.

CONCLUSION

Sustained hypoxemia results in an increase in the anaerobic metabolism of glucose by the preterm fetal brain independent of any change in cerebral oxidative metabolism, which may give rise to an accumulation of lactic acid and contribute to neurologic impairment.

Voltage-sensitive Na+ channels increase in number in newborn rat brain after in utero hypoxia

The effect of chronic in utero hypoxia on voltage-sensitive Na+ channels in newborn rat brain was investigated by means of ligand binding and autoradiography with [3H]saxitoxin (STX, Na+ channel ligand). We found that: (a) binding properties were different between hypoxic and control brains with alinear Scatchard plots in hypoxic brain versus linear ones in the control; (b) STX binding density increased greatly in response to hypoxic stimulation; and (c) the hypoxia-induced increase in STX binding was heterogeneous in various brain areas. We conclude that chronic hypoxia in utero alters the expression of Na+ channels and induces an up-regulation of Na+ channel density as a function of brain area. This is the first report of this phenomenon and we believe that the increased Na+ channels may play an important role in the etiology of neurological disorders such as epilepsy.

Effects of asphyxia on the fetal lamb brain

OBJECTIVE

Our purpose was to study the effect of fetal asphyxia on the release of hypoxanthine and xanthine in cerebrospinal fluid and on brain histologic characteristics.

STUDY DESIGN

In seven fetal lambs (3 to 5 days after surgery, gestational age 124.3 +/- 2.6 days) asphyxia was induced by restriction of uterine blood flow.

RESULTS

Fetal pH and base excess were reduced to 6.99 +/- 0.02 and -17.6 +/- 0.9 mmol/L, respectively. Cerebral blood flow increased during asphyxia and returned to normal in the recovery phase. Maximum concentrations of cerebrospinal fluid hypoxanthine and xanthine were reached in the normoxemic recovery phase. This high level of substrates during normoxemia facilitates oxygen free radical formation and may thus aggravate postasphyctic brain damage. Histologic evaluation of the brain 3 days after the insult showed a variable degree of edema. Coagulative neuronal changes, characteristic of irreversible cell death, were only occasionally detected. These changes were most obvious in the Purkinje cells of the cerebellum.

CONCLUSIONS

Fetal asphyxia induced by uterine blood flow restriction is associated with high levels of cerebrospinal fluid hypoxanthine and xanthine in the recovery phase. Microscopically detectable brain damage, although not extensive, is mainly located in the cerebellum.

Sulfonylurea receptor expression in rat brain: effect of chronic hypoxia during development

Sulfonylurea receptors are believed to be related to ATP-sensitive potassium channels and play a key role during hypoxia/ischemia in the CNS. Our previous work has shown that these receptors in rat brainstem neurons are more important in the adult rat than in the newborn during hypoxia. In the present study, we studied the time course of postnatal development of sulfonylurea receptors in detail and the effect of chronic hypoxia on receptor density in newborn pups and adult rats exposed to hypoxia either as fetuses or as 90-d-old rats using receptor binding and autoradiography. Our current results show that sulfonylurea receptor density 1) was very low at birth and developed fast within the first 2 postnatal wk and then gradually reached adult levels and 2) continued to increase in the cortex and cerebellum but decreased in the brainstem with little or no change in other areas after postnatal wk 5. Chronic hypoxia 1) decreased body weight, brain size, and brain protein concentration and 2) increased sulfonylurea receptor density in utero but had much less of an effect in the adult. From these data, we conclude that sulfonylurea receptors develop mostly in the first 2 wk postnatally and chronic hypoxia increases sulfonylurea receptor expression in utero in spite of the fact that overall protein decreases.

Real time micro-fiberoptic monitoring of endogenous fluorescence in the rat conceptus during hypoxia

A micro-fiberoptic methodology has been developed for non-invasive, real time measurement of endogenous pyridine nucleotide fluorescence from the surface of the visceral yolk sac (VYS) in intact, viable rat conceptuses. Gestational day (GD) 10-12 conceptuses are maintained in a customized perifusion system, which allows for control of oxygenation, as well as the continuous measurement of pH and oxygen concentration in the effluent perifusate. Miniaturized light guides were constructed by drawing 250 microns ESKA acrylic optical fibers through a stainless steel sheath with a high strength epoxy polymer. A single fiber supplied the excitation signal from a mercury arc lamp at a wavelength of 366 nm. The emission signal was returned via three additional fibers, electronically amplified, processed, and recorded, using a dual channel lamp-compensated fluorometer, optimized for detection of reduced pyridine nucleotides at 455 nm. Endogenous fluorescence in the conceptus was monitored by placing the polished tip of the sensor directly on the surface of the VYS. Oxygen-equilibrated conceptuses, exposed to 100% nitrogen, produced a reproducible biphasic surface fluorescence peak, which returned to baseline levels upon reoxygenation of the perifusate. This biphasic response consisted of an initial rapid rise in fluorescence (phase I), followed by an attenuated rate in fluorescence signal increase (phase II). The hypoxia produced age-dependent rates of fluorescence change during phase I, while phase II remained relatively unchanged throughout GD 10-12. These results demonstrate the ability to monitor endogenous fluorescence, non-invasively and in real time, during the period of organogenesis in the intact rat conceptus and will provide valuable information in studies of embryonic metabolism and response to chemical embryotoxicants.

[Limit of antenatal management of intrauterine growth retarded fetus]

Recent advances in perinatal medicine contributed to the survival of extremely premature infants. Nonetheless, prognosis of the fetus with intrauterine growth retardation (IUGR) especially of preterm IUGR is not satisfactory with respect to both neonatal and long term neurodevelopmental outcome. As in utero pathophysiology of the IUGR has been revealed by noninvasive fetal monitoring technique along with invasive cordocentesis to determine fetal blood gas parameters, most of the neonatal morbidity of IUGR is thought to be originated prior to birth. Excluding the IUGR due to chromosomal abnormalities, fetal anomalies and multiple gestation, severe preeclampsia contributes nearly 60 to 80% of the etiology of IUGR in our series. In IUGR with severe preeclampsia, it is noteworthy that the incidence of symmetrical IUGR is approximately 50%, suggesting disturbance in head growth is responsible for symmetrical growth. We have shown that the disturbance in head growth is particularly important not only for neurodevelopmental but also for short term neonatal mortality and morbidity. It is suggested that the reasonable timing of delivery of preterm IUGR should be before onset of fetal acidosis and/or cessation of fetal head growth for the following reasons. 1. There is a relationship between fetal acidemia at cordocentesis and subsequent neurodevelopment. 2. The incidence of neonatal morbidity including hypoglycemia, hemoconcentration and thrombocytopenia increased with the degree of disturbance in head circumference at birth. We propose that the IUGR fetus should be monitored weekly for its growth by ultrasound fetometry and noninvasive fetal monitoring methods including nonstress test, Biophysical profile scoring and Doppler velocimetry.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain cell membrane Na+,K(+)-ATPase modification following hypoxia in the guinea pig fetus

The effect of hypoxia in utero on the affinity of the active sites of Na+,K(+)-ATPase for Na+, K+ and ATP of the fetal guinea pig brain was investigated. Brain cell membranes were prepared from normoxic and hypoxic guinea pig fetuses, and a detailed enzyme kinetics analysis was carried out. In the hypoxic fetal brain membranes the Ka 0.5 for Na+ and K+ increased 104% and 20+, respectively, indicating a decrease in the affinity of the active sites of the enzyme for Na+ and K+. The affinity of the ATP site increased, as indicated by a decrease in the Km of 37% in hypoxic brain. The results indicate that changes in the affinity of active sites would affect the phosphorylation and dephosphorylation mechanisms of the Na+,K(+)-ATPase reaction. The increased affinity for ATP will favor the phosphorylation step, but will be opposed by the decrease in the Na+ affinity. The decreased affinity of the active site for K+ would oppose the dephosphorylation of the enzyme-P complex causing the enzyme to be trapped in an inactive phosphorylated state. The results demonstrated the sensitivity of the Na+,K(+)-ATPase active sites to hypoxia, and illustrated a selective modification of the enzyme active sites under hypoxic conditions, a key mechanism altering the cell membrane function leading to hypoxic brain damage.

The fetal brain: metabolic and circulatory responses to asphyxia

The fetal environment is well suited for normal brain growth and development with oxygen availability well in excess of oxidative needs. With impairments in blood gas exchange, cerebral oxidative metabolism is initially maintained by an increase in cerebral blood flow, thus protecting the 'oxygen margin of safety', and, when this response becomes limited, by an increase in the brain's fractional extraction of oxygen. Additional adaptive mechanisms involve substrate alterations and a decrease in energy consuming processes, including growth restriction and behavioural state alterations. Although protective insofar as essential metabolic functions are maintained, pathologic change may become evident as the 'oxygen margin of safety' becomes limited or energy conserving measures give rise to abnormal growth and development.

NMDA receptor modification in the fetal guinea pig brain during hypoxia

The effect of maternal hypoxia on the modification of the fetal brain cell membrane N-methyl-D-aspartate (NMDA) receptor and its modulatory sites was investigated. Experiments were conducted in pregnant guinea pigs of 60 days of gestation. Guinea pig fetuses were exposed to maternal hypoxia (FiO2 = 7%) for 60 minutes. Tissue hypoxia in the fetal brain was documented biochemically by decreased levels of ATP and phosphocreatine (91.3% and 88.6% lower than normoxia, respectively). MK-801 binding characteristics (Bmax = number of receptors, Kd = affinity of receptor) were used as an index of NMDA receptor modification. P2 membrane fraction was prepared from the cortex of normoxic and hypoxic fetal brain and washed thoroughly before carrying out the binding assay. In hypoxic brains, Bmax decreased from the normoxic control level 0.79 +/- 0.03 pmol/mg protein to 0.58 +/- 0.03 pmol/mg protein (P < 0.005) and Kd value decreased (increased affinity) from 8.54 +/- 0.27 nM to 4.01 +/- 0.23 nM (P < 0.005) respectively. The MK-801 binding in the absence of added glutamate and glycine in hypoxic brain was 100% higher as compared to controls, indicating an increased sensitivity of the NMDA receptor to activation. The spermine dependent maximum activation of the NMDA receptor increased to 44% in the hypoxic animals as compared to 25% in controls. The Mg2+ response of the NMDA receptor was not affected by hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute intrauterine hypoxia increases amniotic fluid prostaglandin F metabolites in the pregnant sheep

OBJECTIVE

Amniotic fluid infection promotes cytokine release, prostaglandin production, and premature labor. In several tissues local hypoxia also activates the secretion of cytokines. Many patients initially seen in premature labor carry small-for-gestational-age fetuses, a condition associated with intrauterine hypoxia. The purpose of our study was to determine whether a reduction in placental blood flow and subsequent acute hypoxia affects prostaglandin secretion by the placenta.

STUDY DESIGN

We chronically catheterized six pregnant sheep at 120 days of gestation. We placed catheters in the maternal and fetal femoral arteries and in the amniotic fluid cavity. A flow probe and snare were placed around the common uterine artery.

RESULTS

A 30-minute uterine circulation occlusion of 30% of its control value produced an increase in prostaglandin F metabolite from 790 +/- 157 to 944 +/- 184 pg/ml within 10 minutes (p < 0.01). Additional uterine blood flow reduction to 60% of control increased the amniotic fluid prostaglandin F metabolites concentration to 894 +/- 202 (p < 0.05, analysis of variance). No increase in mean intrauterine pressure was detected (p > 0.1).

CONCLUSIONS

We speculate that the prostaglandin increase in amniotic fluid in response to intrauterine hypoxia could eventually lead to premature labor. Whether the increase in prostaglandins is mediated by changes in cytokines is unknown at the present time.

Autonomic and arginine vasopressin modulation of the hypoxia-induced atrial natriuretic factor release in immature and mature ovine fetuses

OBJECTIVE

This study investigated the maturational change in the atrial natriuretic factor response to hypoxia in ovine fetuses and the role of the autonomic nervous system and arginine vasopressin in modulating this response.

STUDY DESIGN

Chronically catheterized ovine fetuses from 110 to 135 days' gestation were subjected to 30 minutes of hypoxia. The fetuses were either intact, treated with hexamethonium to block the autonomic nervous system, or treated with a pressor antagonist of arginine vasopressin.

RESULTS

Hypoxia elevated plasma atrial natriuretic factor levels by 1635 +/- 265 pg/ml in immature fetuses; this response was greater than the increase of 748 +/- 189 pg/ml in mature fetuses (p < 0.0001). Blockade of the autonomic nervous system reduced the atrial natriuretic factor response and suppressed the vascular pressure changes to hypoxia in immature but not in mature fetuses. A vasopressin pressor antagonist suppressed the atrial natriuretic factor but not vascular pressure responses to hypoxia in mature fetuses.

CONCLUSIONS

This study demonstrates that the immature fetus manifested a greater atrial natriuretic factor response to hypoxia than did the mature fetus. This enhanced response appeared to be dependent on the modulatory effects of the autonomic nervous system on vascular pressures during hypoxia. In addition, arginine vasopressin appeared to augment the atrial natriuretic factor response to hypoxia in the mature fetus independent of vascular pressure changes.

[Possible reasons for bilirubin accumulation in the brain of newborn animals during oxygen deficiency]

An increase in content of bilirubin was detected in brain tissue of newborn rats with chronic interrupted hypoxic hypoxia occurred during pre- and neonatal periods. Accumulation of bilidiene in animal brain tissues appears to occur due to the following causative factors: tissue acidosis, developed after oxygen deficiency, contributed to binding of bile pigment to brain cell plasma membranes, synaptosomal ones in particular; serum albumin lost its specific ability to bind bilirubin due to protein molecular accumulation of excessive fatty acids and acetaldehyde, which are bound to protein, as well as other minor ligands extracted by organic solvents.

[Physiologic bases of the method to increase nonspecific resistance of the organism by adaptation to intermittent normobaric hypoxia]

Impulse biorhythm of cyclic pO2 change in the uterus tissues and intrauterine fetus of rats, guinea pigs and dogs is regarded as evolution-fixed, physiological mechanism aimed at increasing nonspecific resistance of the fetus. Modeling of this mechanism by adaptation to intermittent normobaric hypoxia under impulse conditions permits more significantly increasing nonspecific resistance of the organism than application of hypoxic effect under constant conditions.

Cerebral energy metabolism in immature and mature guinea pig fetuses during acute asphyxia

In immature fetuses circulatory centralization caused by acute asphyxia is less effective than that in mature fetuses (Jensen & Berger, 1991). This suggests that cerebral oxygenation may be poor in immature fetuses during asphyxia. On the other hand cerebral oxygen consumption is lower in immature than that in mature fetuses. To determine, whether or not there is an imbalance between oxygen supply and demand in one or the other group, we compared the time course of the changes of cerebral concentrations of both high-energy phosphates and glycolytic intermediates between immature and mature guinea pig fetuses during acute asphyxia caused by arrest of uterine blood flow. The fall in the cerebral concentrations of adenosine triphosphate and glucose, and the rise in those of adenosine monophosphate and lactate were slower in immature than in mature fetuses. There were no differences between the levels of cerebral adenosine diphosphate and creatine phosphate of the two groups. From these results we conclude that during acute asphyxia the imbalance between cerebral oxygen supply and demand is less marked in immature than in mature fetuses.

Behavioral and neurochemical sequelae in young rats of antenal hypoxia

To test the hypothesis that perinatal hypoxia may have postnatal consequences via à vis learning memory, and neurochemical sequelae, we exposed pregnant Sprague-Dawley rats to 10.5% O2 for 4 h per day (0800-1200 h) or continuously from gestional day E15 to E20. On E20 we quantified ornithine decarboxylase activity and polyamine concentrations in fetal brain. We also conducted behavioral tests from postnatal day P3 to P110. Relatively mild antenatal hypoxia resulted in altered learning, memory, and delayed maturation of early developmental sensorimotor function. These behavioral changes disappeared at various postnatal ages, depending on the function. Perinatal hypoxia also altered the pharmacological response to dopaminergic drugs. In addition, antenatal hypoxia feminized a male nonreproductive sexual behavior, that of saccharin preference. Acute hypoxia also resulted in an increase in the enzyme ornithine decarboxylase and polyamines, which may affect brain development.

Role of prostaglandins in the metabolic responses of the fetus to hypoxia

OBJECTIVE

The effect of inhibiting prostaglandin synthesis on the fetal metabolic response to hypoxemia was examined by infusing indomethacin during periods of reduced maternal uterine blood flow.

STUDY DESIGN

In seven fetal sheep we administered a 6-hour infusion of either indomethacin (n = 5), indomethacin plus prostaglandin E2, or a vehicle solution (n = 5). The last 4 hours of each infusion period coincided with a period of fetal hypoxemia induced by reduced maternal uterine blood flow.

RESULTS

During reduced maternal uterine blood flow indomethacin infusions caused a significantly greater reduction in pHA (reduced from 7.36 +/- 0.01 to 7.10 +/- 0.02) than both the vehicle (from 7.36 +/- 0.01 to 7.20 +/- 0.03) and indomethacin plus prostaglandin E2 infusions (from 7.36 +/- 0.01 to 7.18 +/- 0.02). Before reduced maternal uterine blood flow was induced, indomethacin significantly elevated fetal plasma glucose and lactate concentrations from 0.6 +/- 0.04 and 2.2 +/- 0.1 to 1.3 +/- 0.2 and 6.7 +/- 0.7 mmol/L, respectively. During reduced maternal uterine blood flow indomethacin caused a significantly greater increase in plasma glucose and lactate concentrations than the vehicle; plasma glucose and lactate concentrations increased to a maximum of 1.8 +/- 0.2 and 22.7 +/- 0.8 mmol/L, respectively, during indomethacin infusions compared with 1.1 +/- 0.1 and 15.7 +/- 1.7 mmol/L, respectively, during vehicle infusions. The addition of prostaglandin E2 to the indomethacin infusion prevented the enhanced increase in glucose and lactate concentrations during reduced maternal uterine blood flow and caused a significant increase in fetal plasma insulin concentrations from 12.6 +/- 0.7 to 60.9 +/- 28.1 microU/ml.

CONCLUSION

The inhibition of prostaglandin synthesis during fetal hypoxemia alters the metabolic response of the fetus, leading to a severe metabolic acidosis.

[Pharmacokinetic examination of theophylline in pregnancy in cases of fetal anoxia]

The purpose of the investigation was to determine the effects of pregnancy on theophylline pharmacokinetics and to clarify the clinical effect of theophylline treatment in cases of threatened anoxemia of foetus. The study was carried out in 15 pregnant women between 28 and 32 weeks of pregnancy with chronic anoxemia of the foetus. The women obtained Aminophyllinum "Polfa" 250 mg (201.3 mg of theophylline) every 12 hours for 4 days to achieve the steady-state of theophylline. After the first dose the drug concentration reached the level of theophylline in range of 12.05 +/- 4.57 micrograms/ml in 15 minutes to 3.62 +/- 0.74 micrograms/ml in 12 hours. The subsequent doses increased the concentration and in steady-state the concentration fluctuates between 21.48 +/- 10.00 micrograms/ml and 6.20 +/- 1.56 micrograms/ml, what coincides with established therapeutic range of theophylline (10-20 micrograms/ml). Elimination of the drug was characterised by calculation of the elimination rate constant and drug-clearance. Both parameters are higher after a single administration what suggest the accumulation of theophylline after multiple drug administration by the saturation of enzymes taking part in metabolism of the drug. Attention should be paid higher values of half-life in pregnancy in comparison with those obtained previously in healthy volunteers. Comparative investigations of the level of theophylline in amniotic fluid in relation to maternal blood in steady-state showed a high correlation between these two values (r = 0.7867, p < 0.006). The proportion of the concentration of theophylline in relation to that in maternal blood is about 60% (0.5978 +/- 0.1599).(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal iron and cytochrome c status after intrauterine hypoxemia and erythropoietin administration

Chronic fetal hypoxemia stimulates erythropoiesis and may result in a redistribution of fetal iron from plasma into erythrocytes. We studied the response of fetal plasma erythropoietin (Ep) to hypoxemia, the role of Ep in stimulating erythropoiesis in utero, and the effect of augmented erythropoiesis on fetal plasma Ep and iron and tissue cytochrome c concentrations in 19 chronically instrumented late-gestation fetal sheep. The fetuses were stimulated to produce 28 erythropoietic responses after exposure to 1) acute hypoxemia (1-5 days), 2) chronic hypoxemia (greater than 7 days), and/or 3) administration of 1,500 U recombinant human Ep concurrently during normoxemia. Plasma Ep peaked less than 12 h after the onset of hypoxemia or Ep bolus. Plasma iron decreased 24-48 h later and returned to baseline 48-96 h after normalization of Ep levels to baseline. The plasma iron response was directly related to the erythropoietin stimulus (r = 0.79, P less than 0.001) and inversely related to liver iron concentration at death (r = -0.84, P less than 0.001). Nine fetuses with depleted liver iron concentrations at autopsy had significantly lower heart and skeletal muscle iron concentrations compared with animals with 10% of control liver iron remaining. Skeletal muscle and heart iron and cytochrome c concentrations were significantly correlated. Ep has a potent biological effect on fetal erythropoiesis and iron metabolism. Augmented fetal erythropoiesis, mediated by Ep, results in decreased plasma iron, hepatic storage iron, and skeletal and cardiac muscle iron and cytochrome c. The model potentially explains the iron abnormalities found in newborn infants after fetal hypoxia.

Cerebral and adrenal monoamine metabolism in the growth-retarded rat fetus under normoxia and hypoxia

The effect of intrauterine growth retardation (IUGR) on cerebral and adrenal monoamine metabolism was studied in the fetuses of eight nulliparous rat dams after unilateral uterine artery ligation on d 18 of gestation. On d 22 (term = 23 d), four dams were subjected to normoxia and four to hypoxia (10% O2) for 58 min while their hemodynamics and blood gases were monitored. An inhibitor of L-aromatic-decarboxylase (3-hydroxybensylhydrazine) was infused to measure monoamine synthesis rate. After decapitation of the dam, fetuses were delivered by sectio, decapitated, and dissected at -5 degrees C. The body, liver, forebrain, brainstem, and adrenal glands were weighed, and concentrations of monoamine precursors, transmitters, and metabolites were assessed in the three latter organs. The weights of liver and forebrain were reduced in fetuses with IUGR, whereas brainstem and adrenal weights were unaltered. Epinephrine content in adrenals was reduced in proportion to body weight under normoxia but failed to increase under hypoxia as it did in appropriately grown fetuses. There were only minor changes in monoamine metabolism in the brainstem. In the forebrain, however, marked changes were seen, mainly in serotonin metabolism: under normoxia, fetuses with IUGR had decreased levels of serotonin and its metabolite 5-hydroxyindole acetic acid. Under hypoxia, appropriately grown fetuses reduced their concentrations of these substances, whereas fetuses with IUGR paradoxically increased their synthetic activity. It is concluded that a disturbance of central nervous serotonin metabolism prevails in growth-retarded rat fetuses in late gestation and that this disturbance depends on the degree of growth retardation and the degree of perinatal stress.

Cerebral lipid peroxidation in the growth retarded rat fetus under normoxia and hypoxia

To detect a possible relationship between the increased vulnerability of the brain of the growth retarded fetus and lipid peroxidation, the activity of the latter was investigated in the forebrain of rat fetuses on day 22 of gestation (term = 23). Growth retardation was induced by uterine artery ligation on day 18. The susceptibility of the forebrain to lipid peroxidation was analysed using the thiobarbituric acid technique after exposure of the awake dams to room air or hypoxia (10% O2) for 58 minutes. Hemodynamics and blood gas status in the dams were stable under conditions of normoxia. When exposed to hypoxia, oxygen availability decreased and blood pressure fell slightly. When normalised for litter, lipid peroxidation covaried with fetal weight in fetuses from normoxic dams, only when Fe2+ (a promotor of lipid peroxidation) was added in the incubation. In fetuses from hypoxic dams, this relationship existed irrespective of whether Fe2+ was present during incubation. In all of these associations, smaller fetuses exhibited more intense lipid peroxidation. In the perinatal period, an increased vulnerability of the central nervous system prevails in growth retarded individuals. An increased tendency to undergo lipid peroxidation and/or a weak defence against this process may be part of the pathophysiologic background.