Effects of maternal betamethasone administration on fetal and maternal blood pressure and heart rate in the baboon at 0.7 of gestation

Lack of effect of antenatal glucocorticoid therapy in the fetal baboon on cerebral cortical glucose transporter proteins

BACKGROUND

Maternal antenatal glucocorticoid therapy is used to accelerate lung maturation of immature babies at risk of preterm delivery. It acutely affects brain activity of the human fetus and reduces the immunoreactivity of neurocytoskeletal and synaptic proteins in the fetal baboon brain. These effects might be based on cerebral energy failure due to a decreased neuronal glucose uptake that has been shown in vitro.

METHODS

Glucose uptake into the brain is selectively facilitated by GLUT1 expressed in the blood-brain barrier and GLUT3 expressed in the neuronal membrane. Immunohistochemical distribution of GLUT1 and GLUT3 were examined in the frontal neocortex of the fetal baboon brain at 0.73 gestation (i.e. similar to 28 weeks of human gestation) after maternal betamethasone administration, mimicking the clinical dose regimen.

RESULTS

Betamethasone did not alter GLUT1 and GLUT3 immunoreactivity.

CONCLUSIONS

The results suggest that inhibition of glucose uptake is not the mechanism for the cerebral effects of antenatal glucocorticoids.

Kinetics of betamethasone and fetal cardiovascular adverse effects in pregnant sheep after different doses

OBJECTIVE

To study the pharmacokinetics of different betamethasone doses and preparations used to enhance fetal lung maturation in the maternal and fetal circulation of sheep and the adverse effects on fetal blood pressure.

METHODS

Doses of 170 (n = 6) and 110 microg/kg (n = 6) betamethasone phosphate equivalent to 12 or 8 mg, respectively, administered to a 70 kg pregnant woman or 170 microg/kg (n = 6) of a depot formulation (50% betamethasone phosphate and 50% betamethasone acetate) were injected intramuscularly to chronically instrumented pregnant sheep.

RESULTS

Both betamethasone preparations produced highest maternal concentrations after 15 min followed by an exponential decline with a t(1/2) of about 3 hours. The drug fell below the limit of detection at 8 to 12 hours. Betamethasone was first detectable in the fetal circulation at 1 hour, peaked at 3 hours, and decreased below the limit of detection at 8 hours independently of the dose or preparation. Maternal and fetal betamethasone concentrations achieved with the phosphate and acetate formulation were one half of those obtained with betamethasone phosphate, suggesting that very little betamethasone is released from the acetate within the first 8 hours when the effect on lung maturation is needed. Betamethasone led to a maximal increase of mean fetal blood pressure from 42+/-1 to 51+/-1 mm Hg (P < .05) and did not differ between the doses and preparations, although plasma concentrations showed a clear dose-concentration relationship.

CONCLUSION

The doses of betamethasone used in obstetrics are supramaximal in terms of cardiovascular effects in sheep. Risk-benefit studies are needed to find the effective steroid dose with the least adverse effects.

Glucocorticoid "Programming" and PTSD Risk

Epidemiological data have linked an adverse fetal environment with increased risks of cardiovascular, metabolic, neuroendocrine, and psychiatric disorders in adulthood. Prenatal stress and/or glucocorticoid excess might underlie this link. In animal models, prenatal stress, glucocorticoid exposure or inhibition/knockout of 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD-2), the feto-placental barrier to maternal glucocorticoids, reduces birth weight and causes permanent hypertension, hyperglycemia, increased hypothalamic-pituitary-adrenal (HPA) axis activity and behavior resembling of anxiety. In humans, 11 beta-HSD-2 gene mutations cause low birth weight and placental 11 beta-HSD-2 activity correlates directly with birth weight and inversely with infant blood pressure. Low birth weight babies have higher plasma cortisol levels throughout adult life, indicating HPA programming. In human pregnancy, severe maternal stress affects the offspring HPA axis and associates with neuropsychiatric disorders. Posttraumatic stress disorder (PTSD) appears to be a variable in the effects. Intriguingly, some of these effects appear to be 'inherited' into a further generation, itself unexposed to exogenous glucocorticoids at any point in the lifespan from fertilization, implying epigenetic marks persist into subsequent generation(s). Overall, the data suggest that prenatal exposure to excess glucocorticoids programs peripheral and CNS functions in adult life, predisposing to some pathologies, perhaps protecting from others, and these may be transmitted perhaps to one or two subsequent generations.

Prenatal glucocorticoid exposure and physiological programming of adult disease

Compelling epidemiological evidence suggests that the early environment is an important determinant of later risk of disease. In particular, low birth weight has been associated with an increased risk of cardiovascular and metabolic disorders, including hypertension, Type 2 diabetes mellitus and ischemic heart disease, independent of classical adult lifestyle risk factors such as smoking, adult weight, social class, excess alcohol intake and sedentary lifestyle. These observations have led to a revolutionary concept of early life physiological programming. The molecular mechanisms that underlie this relationship remain unclear, but one major hypothesis implicates fetal overexposure to glucocorticoid stress hormones. This article will review evidence for this hypothesis.

Nifedipine therapy for preterm labor: effects on placental, fetal cerebral and atrioventricular Doppler parameters in the first 48 hours

OBJECTIVE

To assess the effect of nifedipine tocolysis on Doppler parameters of the uterine, umbilical and fetal middle cerebral arteries and atrioventricular valves in the first 48 h of therapy.

METHODS

Doppler waveforms of uterine, umbilical and middle cerebral arteries and both atrioventricular valves were measured from 28 pregnant women and fetuses prior to and during nifedipine therapy for preterm labor. Maternal and fetal heart rates (FHR), maternal systolic and diastolic blood pressure, and the Doppler pulsatility index (PI) of the uterine, umbilical and middle cerebral arteries were measured. The cerebroplacental ratio (middle cerebral artery PI/umbilical artery PI) was calculated. The total time velocity integrals (TVIs) of tricuspid and mitral valves and their E- and A-wave peak velocity ratio (E/A) were measured. Friedman repeated-measures analysis of variance was used to compare the variables before and after nifedipine therapy. If significant differences were found, Wilcoxon's signed ranks test was used to analyze the difference between the two variables. A P-value of < 0.05 was considered significant.

RESULTS

Nifedipine maintenance was associated with a significant decline in maternal systolic and diastolic blood pressure after 24 h, while maternal heart rate and FHR were unaffected. The uterine artery PI had decreased significantly at 24 and 48 h, while the umbilical artery PI did not change significantly. The middle cerebral artery PI had decreased significantly at 24 and again at 48 h. A significant fall in the cerebroplacental Doppler ratio was maintained beyond 24 h. The mean E/A values, TVIs and TVI x FHR values at 24 and 48 h were unchanged from the baseline values.

CONCLUSIONS

Nifedipine maintenance tocolysis is associated with a significant decline in uterine artery and middle cerebral artery Doppler indices 24 h after the first dose. Fetal cardiac diastolic function is unaffected and the significant redistribution observed after 24 h is likely to be attributable to altered cerebral blood flow.

Effect of 30 per cent maternal nutrient restriction from 0.16 to 0.5 gestation on fetal baboon kidney gene expression

Previous studies in rodents and sheep show that maternal nutrient restriction during pregnancy alters fetal renal development. To date, no studies using fetal baboon RNA with human Affymetrix gene chips have been published. In the present study we have (1) evaluated the specificity of the Affymetrix human gene array 'Laboratory on a Chip' system for use with fetal baboon mRNA and (2) investigated the effects of moderate maternal global nutrient restriction (NR; 70% of ad libitum animals) from early (30 days gestation (dG)) to mid-gestation (90 dG; term = 184 dG) on the fetal baboon kidney. Morphometric and blood measurements were made on 12 non-pregnant baboons before they were bred. All baboons were fed ad libitum until 30 days pregnant, at which time six control baboons continued to feed ad libitum (control - C) while six received 70% of the C diet on a weight adjusted basis. Fetal kidneys were collected following caesarean section at 90 dG, with samples flash frozen and fixed for histological assessment. Fetal hip circumference was decreased in the NR group (68 +/- 2 versus 75 +/- 2 mm), while fetal body weight and all other measurements of fetal size were not different between C and NR at 90 dG. Maternal body weight was decreased in the NR group (12.16 +/- 0.34 versus 13.73 +/- 0.55 kg). Having established the specificity of the Affymetrix system for fetal baboon mRNA, gene expression profiling of fetal kidneys in the context of our maternal nutrient restriction protocol shows that NR resulted in a down-regulation of genes in pathways related to RNA, DNA and protein biosynthesis, metabolism and catabolism. In contrast, genes in cell signal transduction, communication and transport pathways were up-regulated in the NR group. These changes indicate that even a moderate level of maternal global NR impacts fetal renal gene pathways. Our histological assessment of renal structure indicates decreased tubule density within the cortex of NR kidneys compared with controls. The number of glomerular cross-sections per unit area were unaffected by NR, suggesting that tubule tortuosity and/or tubule length was decreased in the NR kidney. Taken together the changes indicate that NR results in accelerated fetal renal differentiation. The negative impact of poor maternal nutrition on the fetal kidney may therefore be in part due to shortening of critical phases of renal growth resulting in decreased functional capacity in later life. These findings may have important implications for postnatal renal function, thereby contributing to the observed increased predisposition to hypertension and renal disease in the offspring of nutrient restricted mothers.

Betamethasone effects on ovine uterine and umbilical placental perfusion at the dose used to enhance fetal lung maturation

OBJECTIVE

The purpose of this study was to examine glucocorticoid effects on umbilical placental perfusion.

STUDY DESIGN

Pregnant sheep instrumented with uterine and umbilical ultrasound transit-time flow probes received 2 doses of 12 mg betamethasone (n = 6) or saline (n = 5) intramuscularly 24 hours apart.

RESULTS

Maternal blood pressure and uterine flow did not change during glucocorticoid exposure. Fetal blood pressure increased, and umbilical resistance showed a transient increase after each injection (P < .05), followed by an increase of umbilical flow (P < .05) that was closely correlated to an increase in fetal heart rate (r = 0.85, P < .001), which determines cardiac output of the developing heart. Umbilical waveform indices were decreased over the entire treatment period, indicating a decrease of resistance in the fetoplacental microcirculation (P < .05).

CONCLUSION

Fetoplacental perfusion during glucocorticoid exposure is not limiting for nutrition exchange. Clinical interpretation of Doppler waveform indices needs to be interpreted with caution because they do not reflect dynamics of umbilical placental perfusion.

The baboon as a good model for studies of human kidney development

Because of the improved survival of premature neonates in recent years, it is important to investigate the effects of premature delivery on the kidney, in which nephrogenesis is still ongoing during the third trimester. Hence, an appropriate animal model that is similar to humans is essential. The aim of the current study is to determine the time course of nephrogenesis in the baboon, to establish whether it is a suitable model of human nephrogenesis. At the Southwest Foundation for Biomedical Research (San Antonio, TX), fetal baboons were delivered prematurely by cesarean delivery and at term by natural delivery. Fixed kidneys from 125-, 140-, 175-, and 185-d gestation baboons were assessed morphologically for evidence of a nephrogenic zone. Nephron number, kidney volume, and glomerular and corpuscle volume were also estimated using unbiased stereology. Morphologic assessment confirmed the presence of metanephric mesenchyme and immature glomeruli in the nephrogenic zone of the kidneys from the prematurely delivered fetuses at 125 and 140 d gestation. At 175 d gestation and at term, the nephrons seemed to be mature. Both kidney weight (R2= 0.918, p = 0.0002) and kidney volume (R2= 0.837, p = 0.001) were very strongly correlated with nephron number. There was also a direct relationship between gestational age (R2= 0.589, p = 0.03) and birth weight (R2= 0.562, p = 0.03) with nephron number. In conclusion, in this study, nephrogenesis in the baboon is complete before term by 175 d gestation, which is similar to humans. Hence, the baboon is a suitable model for future studies to investigate human kidney development.

Glucocorticoid programming

Epidemiological evidence suggests that an adverse fetal environment permanently programs physiology, leading to increased risks of cardiovascular, metabolic, and neuroendocrine disorders in adulthood. Prenatal glucocorticoid excess or stress might link fetal maturation and adult pathophysiology. In a variety of animal models, prenatal glucocorticoid exposure or inhibition of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), the fetoplacental "barrier" to maternal glucocorticoids, reduces birth weight and causes permanent hypertension, hyperglycemia, and increased hypothalamic-pituitary-adrenal axis (HPA) activity and behavior resembling anxiety. In humans, 11beta-HSD2 gene mutations cause low birth weight and reduced placental 11beta-HSD2 activity associated with intrauterine growth retardation. Low birth weight babies have higher plasma cortisol levels throughout adult life, indicating HPA programming. The molecular mechanisms may reflect permanent changes in the expression of specific transcription factors; key is the glucocorticoid receptor itself. Differential programming of the glucocorticoid receptor in different tissues reflects effects upon one or more of the multiple tissue-specific alternate first exons/promoters of the glucocorticoid receptor gene. Overall, the data suggest that either pharmacological or physiological exposure to excess glucocorticoids prenatally programs pathologies in adult life.

Short-term (0-48 h) effects of maternal betamethasone administration on fetal heart rate and its variability

The short-term (0-48 h) effects of maternal betamethasone administration on computerized fetal heart rate (FHR) parameters were studied in 36 pregnancies at increased risk for preterm delivery. FHR was recorded for 90 min immediately before the start of betamethasone treatment and again at 6-h intervals during the next 48 h. Multiple linear regression models were used to assess the possible effects on FHR parameters of gestational age, time of day, clinical indication for treatment, and use of tocolytic drugs. Within 12 h after the start of treatment, significant increases occurred in FHR accelerations, and short- and long-term FHR variability (36%, 28%, and 22%, respectively), whereas basal FHR showed a 5% decrease. FHR variability was decreased by 10% at 42-48 h. The observed changes were more pronounced in older (29-33 wk of gestation) compared with younger fetuses (25-28 wk of gestation). Decelerations occurred only in 4 out of 11 compromised fetuses during betamethasone therapy. We conclude that there are significant changes in FHR parameters during the first 48 h after betamethasone administration. These changes are transient in normal fetuses. However, the compromised fetus may be adversely affected by betamethasone.

Developmental consequences of antenatal dexamethasone treatment in nonhuman primates

Research assessing fetal exposure to dexamethasone and betamethasone in animals has raised concerns about the potential for adverse side effects following antenatal treatments, not withstanding the beneficial and desired improvement in lung function. Some of the inhibitory effects on physical growth and the long-term alterations in endocrine, immune and neural physiology may reflect species differences in the fetal sensitivity of rodents and monkeys to corticosteroids or perhaps could be attributed to the higher drug doses often used in animal studies. However, since steroidal drugs can be administered for extended periods in clinical practice, and also are occasionally given in the range found to cause significant effects on the brain and immune responses of infant monkeys, the simian studies have important cautionary implications for obstetrical and pediatric practice.

Cardiovascular and endocrine effects of a single course of maternal dexamethasone treatment in preterm fetal sheep

OBJECTIVE

To determine the effects of a single course of maternally administered dexamethasone on preterm fetal sheep in utero.

DESIGN

Prospective randomised controlled trial.

SETTING

University laboratory.

SAMPLE

Pregnant sheep at 0.7 of gestation.

METHODS

Pregnant ewes at 103 days of pregnancy (term = 147 days) were given two intramuscular injections of vehicle (n= 7) or 12 mg of dexamethasone (DEX; n= 8) 24 hours apart. Fetuses were continuously monitored for five days.

MAIN OUTCOME MEASURES

Fetal mean arterial blood pressure, carotid and femoral arterial blood flow and vascular resistance, heart rate, heart rate variability, fetal plasma cortisol and ACTH and fetal body movements.

RESULTS

DEX injections led to an acute increase in mean arterial blood pressure with a rise in carotid and femoral vascular resistance, a fall in femoral arterial blood flow, and a brief fall in fetal heart rate followed by significant tachycardia. From 24 hours after the injections, mean arterial blood pressure and vascular resistance returned to control values, however, a mild tachycardia [200 (3) vs 184 (4) bpm, P < 0.05] and loss of the circadian pattern of fetal heart rate variability persisted until the end of recording. Plasma ACTH and cortisol were markedly suppressed by DEX (P < 0.05), with values returning to control levels 32 and 72 hours after the first injection, respectively. There was no effect on basal fetal heart rate variability, body movements, carotid arterial blood flow, or the circadian pattern of fetal heart rate.

CONCLUSION

In contrast to previous experiments utilising direct fetal infusion of steroids, maternal administration of DEX was associated with only transient hypertension.

Betamethasone effects on fetal sheep cerebral blood flow are not dependent on maturation of cerebrovascular system and pituitary-adrenal axis

Synthetic glucocorticoids are administered to pregnant women in premature labour to accelerate fetal lung maturation at a time when fetal cerebrovascular and endocrine systems are maturing. Exposure to glucocorticoids at 0.8-0.9 of gestation increases peripheral and cerebrovascular resistance (CVR) in fetal sheep. We examined whether the increase of CVR and its adverse effect on cerebral blood flow (CBF) depend on the current level of maturation of the pituitary-adrenal axis and the cerebrovascular system. Using fluorescent microspheres, regional CBF was measured in 11 brain regions before and 24 h and 48 h after the start of 3.3 microg kg(-1) h(-1) betamethasone (n = 8) or vehicle (n = 7) infusions to fetal sheep at 0.73 of gestation. Hypercapnic challenges were performed before and 24 h after the onset of betamethasone exposure to examine betamethasone effects on cerebrovascular reactivity. Betamethasone exposure decreased CBF by approximately 40% in all brain regions after 24 h of infusion (P < 0.05). The decline in CBF was mediated by a CVR increase of 111 +/- 16% in the cerebral cortex and 129 +/- 29% in subcortical regions (P < 0.05). Hypercapnic cerebral vasodilatation and associated increase in CBF were blunted (P < 0.05). Fetal CBF recovered after 48 h of betamethasone administration. There were no differences in glucocorticoid induced CBF and CVR changes compared with our previous findings at 0.87 of gestation. We conclude that the cerebrovascular effects of antenatal glucocorticoids are independent of cerebrovascular maturation and preparturient increase in activity of the fetal pituitary-adrenal axis.

Effects of maternally administered dexamethasone and acute hypoxemia at 0.7 gestation on blood pressure and placental perfusion in sheep

Glucocorticoid administration to women in premature labor significantly decreases preterm infant morbidity and mortality. Fetal exposure to maternally administered glucocorticoids in late gestation causes fetal hypertension. We determined the effects of a single course (4 injections at 12-hr intervals) of dexamethasone (DM; 2 mg, a weight-adjusted dose equivalent to one-third the dose administered to pregnant women) or saline (S) in sheep at 103-104 days of gestation (dGA; term 149 dGA) on maternal and fetal blood pressure (BP). We also determined the BP and placental perfusion effects of acute maternal hypoxemia. Venous and arterial catheters were placed in 10 ewes and fetuses (DM = 6, S = 4) at 96 +/- 1 dGA. Maternal and fetal placental perfusion was determined with fluorescent microspheres. Dexamethasone increased fetal but not maternal BP; maternal and fetal placental blood flow and vascular resistance (VR) were unchanged. At 105 dGA, hypoxemia was induced for 1 hr by maternal nitrogen gas inhalation to decrease fetal PaO2 by 40%. Hypoxemia increased BP in DM but not S fetuses or mothers in either group. Hypoxemia decreased maternal placental blood flow by 39 +/- 7% and 51 +/- 9% and increased maternal placental VR by 65 +/- 7% and 69 +/- 6% in S and DM mothers, respectively. Hypoxemia did not alter fetal placental blood flow or VR in either treatment group. In summary, at 0.7 gestation, DM induces a hypertensive response to fetal hypoxemia that is characteristic of older fetuses but does not alter hypoxemia-induced reductions in maternal placental blood flow.

The effects of betamethasone (BM) on endothelial nitric oxide synthase (eNOS) expression in adult baboon femoral arterial endothelial cells

Glucocorticoids have significant effects on endothelium mediated vascular function throughout life. The baboon model has been used extensively to study cellular responses to glucocorticoids at several stages of the lifespan. Endothelial nitric oxide synthase (eNOS) is a major regulator of endothelium dependent arterial vasodilation. We have previously demonstrated that synthetic glucocorticoids down regulate eNOS in the baboon placenta. We have now conducted studies to determine whether glucocorticoids would alter eNOS expression in adult systemic vascular endothelial cells in this important animal model. We explored this potential mechanism in endothelial cells from femoral arteries of adult baboons at necropsy and cultured to the fourth passage. Endothelial cells were treated with 10-100nM betamethasone for 24h at 37 degrees C. Vascular endothelial growth factor (VEGF) was used as a positive control and medium as negative controls. The role of glucocorticoid receptor mediation in betamethasone-induced eNOS changes was investigated with the glucocorticoid receptor antagonist mifepristone. RNA (real-time quantitative RT-PCR) and protein (ELISA) were extracted and measured for eNOS. Expression and subcellular distribution of glucocorticoid receptor were detected with fluorescence labeled antibody microscopy. eNOS mRNA and protein in baboon endothelial cells were downregulated 25% by betamethasone treatment. This effect was attenuated by pre-incubation with mifepristone (P < 0.01). VEGF upregulated eNOS transcription and translation (P < 0.001), medium did not alter eNOS expression. We observed that mifepristone and VEGF increased glucocorticoid receptor cytoplasmic accumulation by fluorescence microscopy. We conclude that betamethasone can downregulate eNOS in cultured baboon endothelial cells via the glucocorticoid receptor pathway.

Effect of antenatal glucocorticoid therapy on arterial and venous blood flow velocity waveforms in severely growth-restricted fetuses

OBJECTIVE

To study the effects of antenatal glucocorticoid (betamethasone) therapy on blood flow velocity waveform patterns in the umbilical artery (UA), middle cerebral artery (MCA) and ductus venosus (DV) in severely intrauterine growth-restricted (IUGR) fetuses.

METHODS

Fifty-five severely IUGR fetuses at 24-34 weeks of gestation were included in the study. The effect of antenatal glucocorticoid administration on Doppler findings in the UA, MCA and DV was studied using two statistical approaches, namely paired sample analysis and multilevel analysis.

RESULTS

There were no effects of betamethasone on the pulsatility index (PI) of the vessels studied. The only changes noticed during the 14 days of observation were a gradual decrease of PI in the MCA, an increase in the UA-PI/MCA-PI ratio and an increase in the DV-PI. These changes with time may be explained by a progressive and gradual deterioration of the fetal condition.

CONCLUSION

Antenatal glucocorticoids (betamethasone) do not affect fetal Doppler waveform patterns of the UA, MCA and DV in severely IUGR fetuses.

Effects of dexamethasone on the uterine and umbilical vascular beds during basal and hypoxemic conditions in sheep

OBJECTIVE

The purpose of the study was to test the hypotheses that maternal treatment with dexamethasone leads to a reduction in basal umbilical blood flow and diminishes the fetal umbilical hemodynamic response to acute hypoxemic stress in sheep.

STUDY DESIGN

While under general anesthesia, 23 ewes and their fetuses were instrumented with vascular catheters and transonic blood flow probes around a uterine and umbilical artery at 117 days of gestation (term, approximately 145 days). At 124 days, the ewes were injected intramuscularly with 2 doses of either dexamethasone (12 mg) or saline solution at 24-hour intervals. All animals experienced 2 episodes of hypoxemia during treatment (125+/-1 days) and after treatment (128+/-1 days).

RESULTS

Maternal dexamethasone treatment caused a sustained increase in fetal arterial blood pressure (from 41+/-3 mm Hg to 45+/-3 mm Hg) and a transient fall in umbilical vascular conductance (from 6.2+/-0.9 mL. min(-1). [mm Hg](-1) to 5.4+/-0.7 mL. min(-1). [mm Hg](-1)). During both episodes of hypoxemia, there was a significant increase in umbilical blood flow in the controls, but not in the dexamethasone-treated animals.

CONCLUSION

Maternal dexamethasone treatment with doses used in human clinical practice significantly decreased basal umbilical vascular conductance and prevented the normal increase in umbilical blood flow that is induced by acute hypoxemia in fetal sheep.

The fetal cardiovascular response to antenatal steroids in severe early-onset intrauterine growth restriction

OBJECTIVE

Our aim was to study the hemodynamic effects of betamethasone on fetuses with intrauterine growth restriction (IUGR) with absent or reversed end-diastolic (ARED) umbilical artery flow.

STUDY DESIGN

Color/pulsed Doppler waveforms were obtained before and after intramuscular injections of betamethasone in 19 consecutive fetuses with IUGR/ARED and 6 control fetuses. Peak velocities and pulsatility index (PI) values were obtained from the umbilical (UA) and middle cerebral (MCA) arteries and intrahepatic umbilical vein (UV).

RESULTS

Ten ARED fetuses developed transient positive umbilical end-diastolic flow after steroids, whereas nine fetuses showed persistent ARED. The persistent ARED subgroup demonstrated increased UA and UV peak velocities after steroids, which may indicate fetal hypertension. Fetal death (n=2) and severe acidosis (n=2) were confined to the subgroup with persistent ARED.

CONCLUSION

Preterm IUGR/ARED fetuses exhibit divergent cardiovascular responses to prenatal steroids. Intensive Doppler-based fetal monitoring may identify a subset of fetuses prone to decompensation after maternal steroid administration.

The effects of antenatal betamethasone administration on fetal heart rate and behaviour depend on gestational age

OBJECTIVE

We previously reported decreases in fetal heart rate (FHR) variability and body and breathing movements after maternal betamethasone administration. We now test the hypothesis that fetal responsiveness to betamethasone depends on the gestational age at which glucocorticoid therapy is started.

DESIGN OF THE STUDY

1-h recordings of FHR (n=350) and fetal movements (n=310) made during a 5-day period (days 0-4) were available for analysis. The recordings had been obtained from 63 pregnant women at high risk for preterm delivery who received betamethasone (two doses of 12 mg 24 h apart) between 26 and 34 weeks' gestational age (wGA). The response to betamethasone, i.e. the direction and magnitude of change in FHR and movement parameters compared with baseline (day 0), was studied in relation to gestational age at drug administration.

RESULTS

Fetuses exposed to betamethasone at 29-34 wGA showed a decrease in FHR on day 1 (indicative of baroreceptor reflex), and reduced breathing activity and prolonged episodes of quiescence with a concomitant decrease in body movements on days 1 and 2. However, these changes were not observed if betamethasone administration occurred at 26-28 wGA. Betamethasone-induced reductions in FHR variability were similar in young and older fetuses.

CONCLUSIONS

Age-related differential responsiveness to betamethasone was found for all studied fetal processes (body and breathing movements, FHR, and quiescence), except FHR variability. Our results suggest ontogenic changes in the mechanisms presumed to underlie these processes (glucocorticoid receptor (GR) maturation, cardiovascular and neuro-endocrine development).

Prenatal dexamethasone leads to both endothelial dysfunction and vasodilatory compensation in sheep

We investigated long-term cardiovascular effects in the offspring of sheep exposed to prenatal dexamethasone (DM). We assessed in vitro vascular responsiveness and evaluated endothelial nitric oxide synthase (eNOS) message and protein levels in femoral muscle removed from 5-month-old sheep. Dexamethasone was administered i.m. to pregnant ewes as 3 weekly courses (4 x 2 mg at 12 h intervals), starting on day 103 of gestation (term approximately 149 days). Ewes were allowed to lamb. At 5 months of age a carotid catheter was placed for blood pressure measurement and hamstring muscle was removed from the lambs under general anaesthesia. We demonstrate that following prenatal DM exposure in the 5-month-old offspring: (1) blood pressure is unchanged; (2) as previously reported in the fetus, sensitivity to endothelin-1 (ET) is increased; (3) acetylcholine-induced relaxation is increased; (4) L-NAME suppressible vasodilatory response to ET is abolished; (5) there is no change in endothelium-independent vasodilatation; and (6) there is no change in eNOS RNA and protein levels, when compared to saline treated controls. We speculate that decreased agonist-induced NO release is not due to alteration in gene expression, but is more likely to be a post-transcriptional event. In summary, the lack of a difference in resting mean arterial pressure (MAP) between DM and control lambs indicates that the compensation we have previously demonstrated in the fetus following glucocorticoid exposure persists to 5 months postnatal age. Compensation is likely due to non-NO-dependent mechanisms, since no evidence was found of upregulated NOS.

Antenatal corticosteroids: the good, the bad and the unknown

PURPOSE OF REVIEW

The purpose of this review was to summarize recently published clinical and animal-based studies of antenatal corticosteroids, describe current recommendations for practice, and suggest priority areas for future research.

RECENT FINDINGS

A single course of antenatal corticosteroids is known to improve newborn lung function after preterm birth and to reduce the risk of newborn death. Current evidence from animal and clinical studies suggests that additional numbers of courses do not further improve lung function and are associated with risks of adverse consequences. These risks principally include restricted intrauterine growth, altered brain development, postnatal insulin resistance and changes to the hypothalamic-pituitary-adrenal axis.

SUMMARY

The research challenges in this field are now centred on uncovering the mechanisms by which cortisol is involved in programming the fetus for its future metabolic life, and discovering ways in which the effectiveness and safety of antenatal glucocorticoids can be enhanced.