Metabolomic profiling of preterm birth in pregnant women living with HIV

BACKGROUND

Preterm birth is a leading cause of death in children under the age of five. The risk of preterm birth is increased by maternal HIV infection as well as by certain antiretroviral regimens, leading to a disproportionate burden on low- and medium-income settings where HIV is most prevalent. Despite decades of research, the mechanisms underlying spontaneous preterm birth, particularly in resource limited areas with high HIV infection rates, are still poorly understood and accurate prediction and therapeutic intervention remain elusive.

OBJECTIVES

Metabolomics was utilized to identify profiles of preterm birth among pregnant women living with HIV on two different antiretroviral therapy (ART) regimens.

METHODS

This pilot study comprised 100 mother-infant dyads prior to antiretroviral initiation, on zidovudine monotherapy or on protease inhibitor-based antiretroviral therapy. Pregnancies that resulted in preterm births were matched 1:1 with controls by gestational age at time of sample collection. Maternal plasma and blood spots at 23-35 weeks gestation and infant dried blood spots at birth, were assayed using an untargeted metabolomics method. Linear regression and random forests classification models were used to identify shared and treatment-specific markers of preterm birth.

RESULTS

Classification models for preterm birth achieved accuracies of 95.5%, 95.7%, and 80.7% in the untreated, zidovudine monotherapy, and protease inhibitor-based treatment groups, respectively. Urate, methionine sulfone, cortisone, and 17α-hydroxypregnanolone glucuronide were identified as shared markers of preterm birth. Other compounds including hippurate and N-acetyl-1-methylhistidine were found to be significantly altered in a treatment-specific context.

CONCLUSION

This study identified previously known as well as novel metabolomic features of preterm birth in pregnant women living with HIV. Validation of these models in a larger, independent cohort is necessary to ascertain whether they can be utilized to predict preterm birth during a stage of gestation that allows for therapeutic intervention or more effective resource allocation.

Approaches to Preventing Intrapartum Fetal Injury

Electronic fetal monitoring (EFM) was introduced into obstetric practice in 1970 as a test to identify early deterioration of fetal acid-base balance in the expectation that prompt intervention ("rescue") would reduce neonatal morbidity and mortality. Clinical trials using a variety of visual or computer-based classifications and algorithms for intervention have failed repeatedly to demonstrate improved immediate or long-term outcomes with this technique, which has, however, contributed to an increased rate of operative deliveries (deemed "unnecessary"). In this review, we discuss the limitations of current classifications of FHR patterns and management guidelines based on them. We argue that these clinical and computer-based formulations pay too much attention to the detection of systemic fetal acidosis/hypoxia and too little attention not only to the pathophysiology of FHR patterns but to the provenance of fetal neurological injury and to the relationship of intrapartum injury to the condition of the newborn. Although they do not reliably predict fetal acidosis, FHR patterns, properly interpreted in the context of the clinical circumstances, do reliably identify fetal neurological integrity (behavior) and are a biomarker of fetal neurological injury (separate from asphyxia). They provide insight into the mechanisms and trajectory (evolution) of any hypoxic or ischemic threat to the fetus and have particular promise in signaling preventive measures (1) to enhance the outcome, (2) to reduce the frequency of "abnormal" FHR patterns that require urgent intervention, and (3) to inform the decision to provide neuroprotection to the newborn.

Maternal Central Blood Pressure Is Associated with Fetal Middle Cerebral Artery Dopplers

Cardiovascular adaptations to pregnancy involve physiological mechanisms that increase cardiac output, decrease total vascular resistance, and decrease both systolic and diastolic blood pressure (BP). These maternal hemodynamic changes modulate uteroplacental blood flow and fetal-placental Doppler indices. Our objective was to create maternal cardiac profiles of pregnant women using non-invasive measurements of central BP to identify changes in maternal-fetal hemodynamics as a surrogate to fetal status. This was a prospective cohort study of all singleton pregnancies in a perinatal referral center between January and April 2018. Central BP was measured non-invasively using the BP+ device. The BP+ device is a supra-systolic oscillometric central BP device, which measures BP waveforms peripherally and calculates central BP. We compared various BP+ values for peripheral BP with central BP and stratified by gestational age. We investigated the correlations between peripheral BP, central BP, estimated fetal weight (EFW), and the pulsatility indices (PI) of Doppler velocimetry and demonstrate that both central systolic and diastolic BP correlated to peripheral systolic and diastolic BP. Linear regression analysis confirmed that central BP predicts the middle cerebral artery (MCA) PI. The MCA PI correlated with EFW, specifically higher central systolic BP is associated with a lower MCA PI, implying a possible etiology of fetal brain shunting with poor placental perfusion. Future studies using predictors and markers of fetal outcomes from maternal cardiac parameters should consider maternal cardiovascular measurements to peripheral arterial BP.

Maternal Fontan procedure is a predictor of a small-for-gestational-age neonate: a 10-year retrospective study

BACKGROUND

Women with single ventricle cardiac physiologic condition who have undergone Fontan procedures are surviving well into reproductive age and historically have been discouraged from pregnancy, despite the paucity of data regarding maternal and neonatal outcomes.

OBJECTIVE

Our primary objective was to investigate, in a large cohort, the maternal and neonatal outcomes of pregnant women who have undergone the Fontan procedure and to understand maternal and neonatal sequelae of their pregnancies.

STUDY DESIGN

This single-center retrospective cohort study involves pregnant women with a Fontan palliation who delivered at UCLA Medical Center over a 10-year period (2007-2017). All pregnancies were evaluated for differences in maternal and neonatal characteristics.

RESULTS

We identified 37 distinct pregnancies in 24 women with a Fontan procedure. The physiologic pregnancy-related increase in cardiac output is blunted substantially in Fontan circulation. Third-trimester cardiac index positively correlated to birthweight z-score (R²=0.48; P=.038) but not to small for gestational age (R²=0.13; P=.339). The most common cardiac complications in pregnancies of >24 weeks gestation were sustained arrhythmia (37.5%) and decompensated heart failure (21%). The 37 pregnancies comprised 25 live births (67.6%), 1 fetal death (2.7%), 9 spontaneous abortions (24%), and 2 pregnancy terminations (5.4%). Of the live births, 60% were preterm at an average gestational age of 34.9±3.7 weeks. Newborn infants were delivered via cesarean in 53%, operative vaginal delivery in 28%, and spontaneous vaginal delivery in 20%. Forty percent of neonates were born small (<10th percentile) for gestational age; 44.0% of all neonates were admitted to the neonatal intensive care unit.

CONCLUSION

Women with a single ventricle and Fontan circulation can have a successful pregnancy, although they are at increased risk for arrhythmias and heart failure. The decreased cardiac reserve in these pregnancies blunts the normal increase in maternal cardiac output, which is associated with preterm delivery and small-for-gestational-age neonates. Further studies are needed to determine to what extent the impaired rise in maternal cardiac output reduces uteroplacental perfusion, placental exchange, fetal growth, and onset of parturition.

Management of Pregnancy in Patients With Complex Congenital Heart Disease: A Scientific Statement for Healthcare Professionals From the American Heart Association

Today, most female children born with congenital heart disease will reach childbearing age. For many women with complex congenital heart disease, carrying a pregnancy carries a moderate to high risk for both the mother and her fetus. Many such women, however, do not have access to adult congenital heart disease tertiary centers with experienced reproductive programs. Therefore, it is important that all practitioners who will be managing these women have current information not only on preconception counseling and diagnostic evaluation to determine maternal and fetal risk but also on how to manage them once they are pregnant and when to refer them to a regional center with expertise in pregnancy management.

Cardiovascular and Neonatal Outcomes in Pregnant Women With High-Risk Congenital Heart Disease

Congenital heart disease (CHD) increases the risk of adverse maternal and neonatal outcomes. However, previous studies have included mainly women with low-risk features. A single-center, retrospective analysis of pregnant women with CHD was performed. Inclusion criteria were the following high-risk congenital lesions and co-morbidities: maternal cyanosis; New York Heart Association (NHYA) functional class >II; severe ventricular dysfunction; maternal arrhythmia, single ventricle (SV) physiology, severe left-sided heart obstruction and severe pulmonary arterial hypertension. Multivariate analyses for predictors of adverse maternal cardiovascular and neonatal outcomes were performed. Forty-three women reported 61 pregnancies. There were no maternal or neonatal deaths. Maternal cardiac (31%) and neonatal (54%) complications were frequent. The most frequent cardiac events were pulmonary edema, arrhythmia, and reduced NYHA class. Previous arrhythmia conferred a 12-fold increase in the odds of experiencing at least one major cardiac complication. Maternal SV physiology was an independent risk factor for low birth weight, risk of neonatal intensive care unit admission and lower gestational age. Maternal cyanosis and severe pulmonary arterial hypertension also predicted adverse neonatal outcomes. In conclusion, mothers without antepartum arrhythmia or functional incapacity are unlikely to experience arrhythmias or a decrease in NYHA class during pregnancy. In addition, SV physiology is a robust predictor of neonatal complications. Antepartum counseling and assessment of maternal fitness are crucial for the woman with CHD.

Thalamic mediation of hypoxic respiratory depression in lambs

Immaturity of respiratory controllers in preterm infants dispose to recurrent apnea and oxygen deprivation. Accompanying reductions in brain oxygen tensions evoke respiratory depression, potentially exacerbating hypoxemia. Central respiratory depression during moderate hypoxia is revealed in the ventilatory decline following initial augmentation. This study determined whether the thalamic parafascicular nuclear (Pf) complex involved in adult nociception and sensorimotor regulation (Bentivoglio M, Balerecia G, Kruger L. Prog Brain Res 87: 53-80, 1991) also becomes a postnatal controller of hypoxic ventilatory decline. Respiratory responses to moderate isocapnic hypoxia were studied in conscious lambs. Hypoxic ventilatory decline was compared with peak augmentation. Pf and/or adjacent thalamic structures were destroyed by the neuron-specific toxin ibotenic acid (IB). IB lesions involving the thalamic Pf abolished hypoxic ventilatory decline. Lesions of adjacent thalamic nuclei that spared Pf and control injections of vehicle failed to blunt hypoxic respiratory depression. Our findings reveal that the thalamic Pf region is a critical controller of hypoxic ventilatory depression and thus a key target for exploring molecular concomitants of forebrain pathways regulating hypoxic ventilatory depression in early development.

Fetal breathing movements and changes at birth

The fetus, which develops within a fluid-filled amniotic sac, relies on the placenta for respiratory gas exchange rather than the lungs. While not involved in fetal oxygenation, fetal breathing movements (FBM) nevertheless have an important role in lung growth and in development of respiratory muscles and neural regulation. FBM are regulated differently in many respects than postnatal respiration, which results from the unique intrauterine environment. Prominent distinctions of FBM include its episodic nature and apnea-sensitivity to hypoxia. The latter characteristic is the basis for using FBM in the assessment of fetuses at risk for hypoxic injury. At birth, the transition to continuous postnatal respiration involves a fall in temperature, gaseous distention of the lungs, activation of the Hering-Breuer reflexes, and functional connectivity of afferent O2 chemoreceptor activity with respiratory motoneurons and arousal centers. Importantly, exposure to drugs or adverse conditions in utero not only can change patterns of FBM but also can lead to epigenetic dysregulation in postnatal respiration. Such changes, can blunt respiratory and arousal defenses against hypoxic challenges in sleep. Thus, fetal hypoxia and/or drug exposure may in later life dispose sleeping infants, children, and adults to hypertension, diabetes mellitus, brain injury, and sudden death.

Adenosine A₂a receptors and O₂ sensing in development

Reduced mitochondrial oxidative phosphorylation, via activation of adenylate kinase and the resulting exponential rise in the cellular AMP/ATP ratio, appears to be a critical factor underlying O₂ sensing in many chemoreceptive tissues in mammals. The elevated AMP/ATP ratio, in turn, activates key enzymes that are involved in physiologic adjustments that tend to balance ATP supply and demand. An example is the conversion of AMP to adenosine via 5'-nucleotidase and the resulting activation of adenosine A(₂A) receptors, which are involved in acute oxygen sensing by both carotid bodies and the brain. In fetal sheep, A(₂A) receptors associated with carotid bodies trigger hypoxic cardiovascular chemoreflexes, while central A(₂A) receptors mediate hypoxic inhibition of breathing and rapid eye movements. A(₂A) receptors are also involved in hypoxic regulation of fetal endocrine systems, metabolism, and vascular tone. In developing lambs, A(₂A) receptors play virtually no role in O₂ sensing by the carotid bodies, but brain A(₂A) receptors remain critically involved in the roll-off ventilatory response to hypoxia. In adult mammals, A(₂A) receptors have been implicated in O₂ sensing by carotid glomus cells, while central A(₂A) receptors likely blunt hypoxic hyperventilation. In conclusion, A(₂A) receptors are crucially involved in the transduction mechanisms of O₂ sensing in fetal carotid bodies and brains. Postnatally, central A(₂A) receptors remain key mediators of hypoxic respiratory depression, but they are less critical for O₂ sensing in carotid chemoreceptors, particularly in developing lambs.

Adenosine A1 and A2a receptors modulate insulinemia, glycemia, and lactatemia in fetal sheep

Adenosine A(1) and A(2A) receptor subtypes modulate metabolism in adult mammals. This study was designed to determine the role of these receptors in regulating plasma levels of insulin, glucose, and lactate in 20 chronically catheterized fetal sheep (>0.8 term). In normoxic fetuses (Pa(O(2)) approximately 24 Torr), systemic blockade of A(1) receptors with DPCPX (n = 6) increased plasma concentrations of insulin, glucose, and lactate, but antagonism of A(2A) receptors with ZM-241385 (n = 5) had no significant effects. Intravascular administration of adenosine (n = 9) reduced insulin concentrations and elevated glucose and lactate levels. DPCPX (n = 6) augmented the glycemic and lactatemic responses of adenosine. In contrast, ZM241385 (n = 5) virtually abolished adenosine-induced hyperglycemia and hyperlactatemia. Isocapnic hypoxia (Pa(O(2)) approximately 13 Torr) suppressed insulinemia and enhanced glycemia and lactatemia, but only the hyperglycemia was blunted by blockade of A(1) (n = 6) or A(2A) (n = 6) receptors. We conclude that 1) endogenous adenosine via A(1) receptors depresses plasma concentrations of insulin, glucose, and lactate; 2) exogenous adenosine via A(2A) receptors increases glucose and lactate levels, but these responses are dampened by stimulation of A(1) receptors; and 3) hypoxia, which increases endogenous adenosine concentrations, induces hyperglycemia that is partly mediated by activation of A(1) and A(2A) receptors. We predict that adenosine, via A(1) receptors, facilitates at least 12% of glucose uptake and utilization in normoxic fetuses.

Increased senescence and reduced functional ability of fetal endothelial progenitor cells in pregnancies complicated by preeclampsia without intrauterine growth restriction

OBJECTIVE

The aim of this study was to investigate the number and functional ability of fetal endothelial progenitor cells in pregnancies complicated by preeclampsia without intrauterine growth restriction.

STUDY DESIGN

Fetal endothelial progenitor cells were isolated, and counted from 17 women with preeclampsia without intrauterine growth restricion and 30 normal women. Colony-forming assay and differentiation time assay were performed to detect functional activity of the cells. To assess cellular senescence, senescence-associated beta-galactosidase staining was performed for endothelial progenitor cells.

RESULTS

Compared with normal pregnancy, the number of endothelial progenitor cells was significantly lower, differentiation time from endothelial progenitor cell into outgrowing cell was longer, and the number of colonies after differentiation was smaller in preeclampsia (P< .001), respectively. The intensity of senescence-associated beta-galactosidase staining was higher in preeclamptic pregnancy (P < .001).

CONCLUSION

The number and functional ability of fetal endothelial progenitor cells from preeclampsia without intrauterine growth restriction are significantly decreased and they are more senescent compared with those of normal pregnancy.

Characterization of [125I]ZM 241385 binding to adenosine A2A receptors in the pineal of sheep brain

Adenosine is a ubiquitous neuromodulator and homeostatic regulator that exerts its physiologic actions through activation of A(1), A(2A), A(2B) and A(3) adenosine receptor subtypes. In the central nervous system, adenosine's action in neurons is manifested in its modulation of tonic inhibitory control. Adenosine released in the brain during hypoxia has critical depressant effects on breathing in fetal and newborn mammals, an action suggested to be mediated by A(2A) receptors in the posteromedial thalamus. In an effort to more accurately define the spatial distribution of adenosine A(2A) receptors in fetal sheep diencephalon, we have used a receptor autoradiographic technique utilizing an iodinated radioligand [(125)I]ZM 241385, which has greater sensitivity and resolution than the tritiated compound. The distribution of ligand binding sites in the fetal sheep diencephalon indicated that the highest levels of binding were in select thalamic nuclei, including those implicated in hypoxic depression of fetal breathing, and the pineal. Given the high density of labeled A(2A) receptors in the pineal, these sites were characterized more fully in homogenate radioligand binding assays. These data indicate that [(125)I]ZM 241385 binding sites display a pharmacological signature consistent with that of adenosine A(2A) receptors and are expressed at similar levels in fetal, lamb and adult ovine brain. The adenosine A(2A) receptor pharmacologic signature of the [(125)I]ZM 241385 binding site in pineal cell membranes generalized to the site characterized in membranes derived from other portions of the lamb thalamus, including the sector involved in hypoxic inhibition of fetal breathing. These results have important implications for the functional roles of adenosine A(2A) receptors in the thalamus and pineal of sheep brain.

Ultrasound and fetal diagnosis

PURPOSE OF REVIEW

The purpose of this review is to highlight publications from the last year that have advanced the use of ultrasound in obstetrics.

RECENT FINDINGS

Anatomic examination of the fetus in the first trimester has been emphasized because it allows for early diagnosis of many conditions. The prevalence of absent nasal bone, a marker for trisomy 21, in euploid fetuses depends on ethnicity. Nasal bone hypoplasia is another marker for Down syndrome. Studies on genetic screening in the first trimester have involved various serum analytes, adjustments in timing and calculations, use in multiple gestations, and the association of extreme measurements with adverse outcomes. A first-trimester integrated screening approach, which incorporates nuchal translucency, nasal bone, crown-rump length, pregnancy-associated plasma protein-A, and free beta-human chorionic gonadotropin, has the potential to maximize detection rates of Down syndrome and trisomy 18 and minimizes the screen-positive rate. The value of combining first and second-trimester results in sequential, contingent, or integrated screening protocols has been assessed. Isolated mild ventriculomegaly (10-12 mm) may prove to be a normal variant, and the role of 'soft' ultrasound markers in genetic counseling continues to be debated. Anomaly or high-risk status detection in the second trimester has been enhanced by the use of Doppler, 3D/4D ultrasound, and magnetic resonance imaging.

SUMMARY

Imaging techniques have been critical in the development of screening methods for Down syndrome or trisomy 18 and for euploid fetuses at high risk for adverse outcomes.

Adenosine A2A-receptor blockade abolishes the roll-off respiratory response to hypoxia in awake lambs

Adenosine (ADO) receptor antagonists (aminophylline, caffeine) blunt the respiratory roll-off response to hypoxia in the newborn. This study was designed to determine the ADO receptor subtype involved in the respiratory depression. Chronically catheterized lambs of 7–16 days of age breathed via face mask a gas mixture with a fraction of inspired O2 of 0.21 (normoxia) or 0.07 (hypoxia), while being infused intravascularly with 9-cyclopentyl-1,3-dipropylxanthine (DPCPX; ADO A1-receptor antagonist, n = 8), ZM-241385 (ADO A2A-receptor antagonist, n = 7), or vehicle. Ventilation was measured at 20°C by a turbine transducer flowmeter. In normoxia [arterial Po2 (PaO2) of ∼83 Torr], infusion of vehicle did not alter cardiorespiratory measurements, whereas hypoxia (PaO2 of ∼31 Torr, 15 min) elicited biphasic effects on mean arterial pressure (transient increase), heart rate (HR; diminishing tachycardia), and minute ventilation. In the latter, hypoxia increased ventilation to a peak value of ∼2.5 times control within the first 3 min, which was followed by a significant ( P < 0.05) decline to ∼50% of the maximum increment over the subsequent 7 min. ZM-241385 abolished the hypoxic ventilatory roll-off and blunted the rate of rise in HR without affecting mean arterial pressure or rectal temperature responses. In normoxia, DPCPX increased ventilation and mean arterial pressure but did not change HR. Compared with vehicle, DPCPX did not significantly affect cardiorespiratory responses to hypoxemia (PaO2 of ∼31 Torr, 10 min). It is concluded that 1) ADO A2A receptors are critically involved in the ventilatory roll-off and HR responses to hypoxia, and 2) ADO A1 receptors, which are tonically active in cardiorespiratory control in normoxia, appear to have little impact on hypoxic ventilatory depression.

Induced fetal depressor or pressor responses associated with c-fos by intravenous or intracerebroventricular losartan

Previous fetal studies have indicated depressor responses of intravenous (i.v.) administration of angiotensin antagonists. However, little is known of central effects of angiotensin blockers on fetal cardiovascular controlling. The cardiovascular effects of central administration of the angiotensin-1 (AT(1)) and angiotensin-2 (AT(2)) receptor antagonists, losartan and PD123319, were investigated in the chronically catheterized near-term ovine fetuses. Intravenous losartan produced within 1.5 min a significant and persistent depressor response [maximum Delta mean arterial pressure (MAP)=9 mm Hg] without altering fetal heart rate. Intracerebroventricular (i.c.v.) administration of losartan (1-5 mg/kg) increased fetal arterial pressures (Delta MAP=9-14 mm Hg). Central application of losartan (1 mg/kg) also increased fetal heart rate (maximum Delta heart rate=33 beat per minute). Losartan increased c-fos expression in the median preoptic nucleus and paraventricular nuclei in the forebrain, and the tractus solitarius nuclei, the lateral parabrachial nuclei, and the ventrolateral medullabrain. These brain sectors are with abundant AT(1) receptors and have been demonstrated in the involvement in cardiovascular regulation. In contrast, intracerebroventricular injection of the AT(2) receptor antagonist PD123319 had no effect on fetal arterial pressure and heart rate. The results demonstrate strikingly functional differences of losartan on the fetal cardiovascular regulation in central and peripheral sides.

Electrical stimulation of the posteromedial thalamus modulates breathing in unanesthetized fetal sheep

Having previously shown that lesions in the posteromedial group of thalamic nuclei abolish hypoxic inhibition of fetal breathing, we devised this study to identify thalamic loci that depress breathing by focal stimulation of specific sectors of the caudal thalamus and adjacent structures. Multipolar electrode arrays consisting of a series of eight stimulation contacts at 1.25-mm intervals were implanted vertically through guide cannulae into the caudal diencephalon of 12 chronically catheterized fetal sheep (>0.8 term), and central neural tissue was stimulated between adjacent contacts. Each site was stimulated repeatedly with increasing current searching for spatial and stimulus strength parameters for a reliable alteration in respiratory rate. Respiratory period increased when stimulation involved areas of the parafascicular nuclear complex (Pf), which more than doubled the mean period compared with the baseline of 0.90 ± 0.19 s. The change in respiratory period was due to an increase in expiratory time, whereas inspiratory time and breath amplitude were not significantly affected. Breathing period and expiratory time were also increased when the stimulations involved the intralaminar wing surrounding the mediodorsal nucleus, the rostral central gray, zona incerta, and ventral tegmental area. Reductions in respiratory frequency occurred less consistently, with stimulation involving surrounding zones including the sub-Pf, ventromedial nucleus, and ventrobasal nuclear complex. These findings support the hypothesis that a restricted area of the posteromedial thalamus (principally Pf) constitutes part of a neuronal circuitry that modulates respiratory motoneurons.

Adenosine A(2A) receptors mediate hypoxic inhibition of fetal breathing in sheep

OBJECTIVE

Hypoxia inhibits fetal breathing through activation of central adenosine (ADO) receptors that modulate fetal behavioral state. This study was designed to determine whether adenosine A(1) and/or A(2A)receptor subtypes mediate the depressant effects of hypoxia.

STUDY DESIGN

In 14 chronically catheterized fetal sheep (>0.8 term), hypoxemia was induced by having the ewe breathe a gas mixture of 9% oxygen for 1 hour. During hypoxia, the fetus was infused intra-arterially with a vehicle or an antagonist for adenosine A(1) or A(2A) receptors. Statistical analysis was performed by using analysis of variance with Tukey's least significant difference criterion.

RESULTS

Fetal isocapnic hypoxemia (PaO(2): control, approximately 24 mm Hg; hypoxia, approximately 14 mm Hg) virtually eliminated rapid eye movements and breathing when the fetus was infused with vehicle or the A(1) receptor antagonist. In contrast, adenosine A(2A) receptor blockade abolished the hypoxia-induced arrest of rapid eye movements and breathing.

CONCLUSION

Hypoxic inhibition of rapid eye movements and breathing is critically dependent on activation of adenosine A(2A) receptors.

Placental calcification: a metastatic process?

Placental calcification commonly increases with gestational age. The mechanism of apatite mineralization probably involves one of three known mechanisms of tissue calcification: physiological (like bone), dystrophic (ischaemia-related) or metastatic (mineralization in a supersaturated environment). This study was designed to determine the mechanism of calcification by examining (1) the mineral content of placental calcifications in comparison to other physiological and pathological apatites, and (2) the expression of bone morphogenetic proteins (BMPs), which are important in physiological calcification, across gestational age. By energy-dispersive x-ray analysis (EDXA), the Ca/P weight ratio for apatitic mineral from mature calcifications was 2.00+/-0.05 (s.e.), which is similar to that for stones formed in a metastatic, supersaturated environment and lower than that observed in physiological calcification. Biologically active BMP, which was determined by bioassay, was demonstrated in mature and postmature placentae. The BMPs PLAB, PDF and related protein INSL-4 were identified by semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR), but their mRNA expression was independent of gestational age (7-41 weeks of gestation). We conclude that (1) the identified BMPs were not related directly to placental calcification, which argues against physiological calcification, and (2) the chemical composition of the apatitic mineral was suggestive of rapid formation in a supersaturated environment, which is consistent with a metastatic mechanism of calcification.

Adenosine A(1) and A(2A) receptors modulate sleep state and breathing in fetal sheep

This study was designed to determine the adenosine (Ado) receptor subtype that mediates the depressant effects of Ado on fetal breathing and rapid eye movements (REM). In chronically catheterized fetal sheep (>0.8 term), intra-arterial infusion of N(6)-cyclopentyladenosine (CPA), an Ado A(1)-receptor agonist, increased the incidence of high-voltage electrocortical (ECoG) activity while virtually abolishing low-voltage activity, REM, and breathing. These effects were blocked by 9-cyclopentyl-1,3-dipropylxanthine (DPCPX), an Ado A(1)-receptor antagonist. Infusion of DPCPX alone increased breath amplitude but had no significant effect on inspiratory duration, breath interval, incidence of REM, or incidence of low-voltage activity. Ado A(2A)-receptor blockade with ZM-241385 increased the incidence of low-voltage ECoG activity, REM, and breathing but had no effect on breath amplitude or respiratory cycle. Both DPCPX and ZM-241385 eliminated the inhibitory effects of Ado on REM and breathing. We conclude that 1) Ado A(1) receptors tonically inhibit fetal respiratory drive, 2) Ado A(2A) receptors tonically inhibit REM-like behavioral state, and 3) both Ado A(1) and A(2A) receptors mediate the depressant effects of Ado on REM and breathing.

Adenosine A(2A) receptors mediate cardiovascular responses to hypoxia in fetal sheep

Nonselective adenosine (ADO) receptor antagonists block hypoxia-induced bradycardia and hypertension in fetal sheep. This study was designed to determine the ADO receptor subtype that is involved in these cardiovascular responses. In chronically catheterized fetal sheep (>0.8 term), fetal hypoxemia was induced by having the ewe breathe a hypoxic gas mixture (9% O(2)-3% CO(2)-88% N(2)) for 1 h. Intra-arterial infusion of ZM-241385, an antagonist highly selective for ADO A(2A) receptors, to eight fetuses during normoxia significantly increased mean arterial pressure (MAP) from 42.5 +/- 2.0 to 46.1 +/- 2.0 mmHg without altering heart rate (HR). Infusion of a selective antagonist of ADO A(1) receptors [1, 3-dipropyl-8-cyclopentylxanthine (DPCPX)] elevated MAP and HR only after the infusion was terminated, although administration of the vehicle for ZM-241385 or DPCPX had no effect on MAP or HR. Isocapnic hypoxia with infusion of DPCPX or the vehicle for DPCPX or ZM-241385 produced a transient fall in HR, a rise in MAP, and a decrease in plasma volume. In contrast, ADO A(2A) receptor blockade abolished the hypoxia-induced bradycardia and hypertension and blunted the decline in plasma volume. We conclude that fetal ADO A(2A) receptors: 1) modulate AP during normoxia, and 2) mediate cardiovascular responses during acute O(2) deficiency.

Thalamic lesions dissociate breathing inhibition by hypoxia and adenosine in fetal sheep

The effects of diencephalic lesions on respiratory responses to intra-arterially infused adenosine (ADO) were determined in chronically catheterized fetal sheep (>0.8 term). These studies were designed to test the hypothesis that the inhibitory effects of ADO on fetal breathing, like those of hypoxia, are mediated by the parafascicular nuclear complex (Pf) of the posteromedial thalamus. ADO inhibited breathing [control (C): 26 +/- 2.6, ADO: 4 +/- 1 min/h] in normal fetuses and in a fetus with a lesion that virtually destroyed the thalamus but left intact most of Pf. Neuronal lesions in the diencephalon, produced by injecting ibotenic acid, abolished the inhibitory effects of ADO on breathing (C: 31 +/- 5.1, ADO: 30 +/- 4.5 min/h) when the lesions encompassed Pf or the sector immediately rostral to Pf that retained the capacity to regulate hypoxic inhibition. Smaller lesions created by the insertion of needles also eliminated the depressant effects of ADO when disruptions were within Pf or a rostral component of the thalamic cortical activating system. It is concluded that 1) a medial thalamic sector is critically involved in ADO-induced apnea and 2) ADO-dependent and ADO-independent mechanisms mediate hypoxic inhibition.

Metabolic and cardiorespiratory responses to hypoxia in fetal sheep: adenosine receptor blockade

8-Phenyltheophylline (PT), a potent and specific inhibitor of adenosine receptors, was infused intra-arterially into unanesthetized fetal sheep to determine the role of adenosine in hypoxic inhibition of fetal breathing. PT in normoxic fetuses increased heart rate and the incidence of low-voltage electrocortical activity, rapid eye movements (REM), and breathing. Mean breath amplitude increased by 44%. Hypoxia (preductal arterial PO2 = 14 Torr) induced a metabolic acidemia, a transient bradycardia, and hypertension while virtually eliminating REM and breathing. PT administration during hypoxia enhanced the metabolic acidemia, blocked the bradycardia and hypertension, increased the incidence of REM and breathing, and elevated mean breath amplitude. The results indicate that 1) adenosine is involved in fetal glycolytic and cardiovascular responses to hypoxia, 2) activation of central adenosine receptors mediates about one-half the inhibitory effects of hypoxia on REM and breathing, and 3) the depression of breathing may critically depend on a hypoxia-induced reduction in phasic REM sleep.

Adenosine modulates corticotropin and cortisol release during hypoxia in fetal sheep

OBJECTIVE

This study was designed to determine the role of adenosine in the hypoxic release of corticotropin in fetal sheep.

STUDY DESIGN

The adenosine receptor antagonist 8-phenyltheophylline or the vehicle was infused intra-arterially to chronically catheterized fetal sheep (>0.8 term) during an hour of fetal hypoxemia (Pa O 2 congruent with 14 mm Hg). Control studies were also performed in which 8-phenyltheophylline or the vehicle was administered to normoxic fetuses.

RESULTS

8-Phenyltheophylline abolished hypoxia-induced bradycardia and hypertension and produced a nearly 5-fold greater rise in fetal plasma concentrations of corticotropin and approximately a 3-fold greater increase in plasma cortisol levels. During normoxia 8-phenyltheophylline increased plasma cortisol concentrations by 2-fold without altering corticotropin levels, mean arterial blood pressure, or heart rate.

CONCLUSION

Adenosine blunts fetal corticotropin release during hypoxia, which in turn reduces cortisol secretion. At lower corticotropin concentrations, adenosine also appears to dampen the cortisol response through direct effects on the adrenals.

Thalamic locus mediates hypoxic inhibition of breathing in fetal sheep

The effects of lesions rostral to the brain stem on breathing responses to hypoxia were determined in chronically catheterized fetal sheep (>0.8 term). These studies were designed to test the hypothesis that the diencephalon is involved in hypoxic inhibition of fetal breathing. As in normal fetuses, hypoxia inhibited breathing with transection rostral to the thalamus or transection resulting in virtual destruction of the thalamus but sparing most of the parafascicular nuclear complex. Neuronal lesions were produced in the fetal diencephalon by injecting ibotenic acid through cannulas implanted in the brain. Hypoxic inhibition of breathing was abolished when the lesions encompassed the parafascicular nuclear complex but was retained when the lesions spared the parafascicular nuclear region or when the vehicle alone was injected. A new locus has been identified immediately rostral to the midbrain, which is crucial to hypoxic inhibition of fetal breathing. This thalamic sector involves the parafascicular nuclear complex and may link central O2-sensing cells to motoneurons that inhibit breathing.

Fetal cardiovascular and breathing responses to an adenosine A2a receptor agonist in sheep

CGS-21680 (CGS), a highly selective adenosine A2a receptor agonist, may excite the fetal carotid bodies. This study was designed to determine 1) whether CGS stimulates fetal breathing and 2) whether sinoaortic denervation abolishes CGS-induced tachycardia. In eight intact fetuses (> 0.8 term), intra-arterial CGS infusion (6 micrograms.min-1.kg estimated fetal wt-1) increased mean arterial PCO2 by 3-7 Torr, reduced fetal arterial PO2 by 2-5 Torr, and produced a mild metabolic acidemia. Heart rate increased from 154 +/- 7 (control) to 249 +/- 12 beats/min, but mean arterial pressure was not significantly affected. CGS initially increased the frequency, amplitude, and incidence of fetal breathing, but this hyperpnea was followed by prolonged respiratory depression that was not reversed with blockade of adenosine A1 receptors. Denervation of both carotid bodies together with interruption of the vagi abolished the hyperpnea without altering the respiratory depression or the maximum rise in heart rate. We conclude that CGS induces 1) tachycardia by a mechanism independent of the peripheral arterial chemoreceptors, 2) hyperpnea by stimulating peripheral adenosine A2a receptors, and 3) respiratory depression by activating central A2a receptors.

Source of extracellular brain adenosine during hypoxia in fetal sheep

Microdialysis was performed to determine whether hypoxia increases fetal brain adenosine (ADO) concentration through dephosphorylation of extracellular 5'-adenosine monophosphate (5-AMP). Hypoxia (fetal PaO2 approximately 14 Torr) increased fetal brain ADO levels approximately two-fold when the probes were perfused with synthetic cerebrospinal fluid (CSF) containing inhibitors of the nucleoside transporter but not with this solution plus a blocker of ecto-5'-nucleotidase (AOPCP). The hypoxia-induced rise in fetal brain ADO concentrations depends critically upon the hydrolysis of extracellular 5'-AMP.

Enhancing adenosine A1 receptor binding reduces hypoxic-ischemic brain injury in newborn rats

Hypoxia increases brain adenosine concentrations, which provides neuroprotection through activation of central adenosine A1 receptors. This study was carried out to determine whether PD 81,273, which increases adenosine's binding to A1 receptors, would reduce hypoxia-induced brain injury. PD 81,273 (3 mg/kg, i.p.) decreased by about 50% the weight loss of the left cerebral hemisphere caused by hypoxia-ischemia in neonatal rats. Thus, enhancing adenosine's binding to the A1 receptor decreases hypoxic brain damage.

Pregnancy outcomes after the Fontan repair

OBJECTIVES

This study sought to determine risks and outcome of pregnancy and delivery after the modified Fontan operation.

BACKGROUND

Increasingly, female Fontan patients reaching child-bearing years are interested in having children. To date, the number of reported pregnancies is small, and pregnancy has therefore been discouraged.

METHODS

One hundred ten of 126 female patients from the Fontan registries of the Mayo Clinic and University of California Los Angeles Medical Center responded to a mailed questionnaire. An additional six patients with a reported pregnancy from other centers were identified and reviewed to assess pregnancy outcomes.

RESULTS

Among the participating centers, a total of 33 pregnancies after Fontan operation for various types of univentricular heart disease were reported. There were 15 (45%) live births from 14 mothers, with 13 spontaneous abortions and 5 elective terminations. In the 14 women with live births, the median number of years between operation and pregnancy was 4 (range 2 to 14). Reported prepregnancy problems in these gravidas included atrial flutter in one patient and ventricular dysfunction, aortic regurgitation and atrioventricular valve regurgitation in another. One patient developed supraventricular tachycardia during pregnancy and had conversion to sinus rhythm. No maternal cardiac complications were reported during labor, delivery or the immediate puerperium. There were six female and nine male infants (mean gestational age 36.5 weeks; median weight 2,344 g). One infant had an atrial septal defect. At follow-up, mothers and infants were alive and well.

CONCLUSIONS

Pregnancy after the Fontan operation appears to have been well tolerated in 13 to 14 gravidas. There does appear to be an increased risk of miscarriage. The tendency to routinely discourage pregnancy may need to be reconsidered.

Adenosine mediates metabolic and cardiovascular responses to hypoxia in fetal sheep

1. In seven unanaesthetized fetal sheep (> 80% term), isocapnic hypoxia (arterial partial pressure of O2, Pa,O2, approximately 15 mmHg) was induced for 1 h by lowering maternal inspired PO2. Fetal hypoxia was also produced during intra-arterial administration of the adenosine receptor antagonist 8-(p-sulphophenyl)-theophylline (8-SPT). The fetal 8-SPT infusion was begun just prior to hypoxia and was stopped when fetal Pa,O2 was returned to normal. 2. Hypoxia induced a progressive fetal acidosis, a rise in mean arterial pressure, a transient fall in heart rate and a decrease in breathing movements. 8-SPT significantly reduced the metabolic acidosis and abolished the hypertension and bradycardia without altering hypoxic inhibition of fetal breathing. Administration of the vehicle for 8-SPT during hypoxia did not significantly affect the normal fetal metabolic and cardiovascular responses to acute O2 deprivation. 3. It is concluded that adenosine mediates the fetal bradycardia and hypertension produced by hypoxia, indicating that adenosine modulates fetal autonomic responses to acute oxygen deficiency. Secondly, adenosine contributes to fetal metabolic acidaemia, suggesting that adenosine also modulates fetal glycolytic responses to hypoxia.

Adenosine modulates hypoxia-induced atrial natriuretic peptide release in fetal sheep

The effects of adenosine on atrial natriuretic peptide (ANP) secretion were determined in chronically catheterized fetal sheep (> 0.8 term). Adenosine was infused into the the right jugular vein for 1 h at 8 +/- 0.4 (5 fetuses), 160 +/- 8 (6 fetuses), and 344 +/- 18 micrograms.min-1.kg estimated fetal wt-1. Fetal arterial blood gases and pH were generally unaffected by adenosine, although mean arterial CO2 tension increased transiently by 2-5 Torr and pH fell progressively during the highest rate of infusion. During the intermediate and high infusion rates, fetal hemoglobin concentrations increased by 11-13% and mean fetal heart rate rose by 18% from a control value of approximately 167 beats/min. Mean arterial pressure was not affected during adenosine infusion. Adenosine significantly increased fetal plasma ANP levels, with maximum concentrations 1.80, 2.36, and 2.51 times greater than control means (142-166 pg/ml) for the respective infusion rates of 8, 160, and 344 micrograms.min-1.kg estimated fetal wt-1. In seven fetuses, reducing fetal arterial O2 tension by approximately 9-10 Torr from a control of 23 +/- 1.3 Torr increased plasma ANP concentrations approximately 2.4 times the control mean of 176 pg/min. Adenosine-receptor blockade with 8-(p-sulfophenyl)-theophylline reduced by 50% the maximum hypoxia-induced rise in plasma ANP concentrations. It is concluded that adenosine causes a dose-dependent rise in fetal plasma ANP concentrations and modulates fetal ANP release during hypoxia.

Predictive value of HemoCue capillary whole blood glucose measurements in pregnancy

OBJECTIVE

We determined the ability of capillary whole blood glucose concentrations to predict venous plasma and whole blood glucose levels.

METHODS

During a standard oral glucose tolerance test in 29 pregnant women, paired capillary and venous blood samples were collected for analysis of glucose concentrations by the HemoCue photometer and by central laboratory methods.

RESULTS

Glucose concentrations determined serially in a single blood sample by the HemoCue method were highly reproducible, with a coefficient of variation of 2.3%. However, glucose levels in blood from two different fingersticks from the same patient varied on average by 3 mg/dL, with a maximum difference of 14 mg/dL. Although capillary whole blood glucose results obtained by the HemoCue method correlated well with venous plasma or whole blood glucose measurements (r = 0.98 and r = 0.97, respectively) over the range investigated (60-250 mg/dL), individual capillary whole blood glucose measurements were only a fair predictor of venous values, with 95% of measured venous levels within +/- 26 mg/dL and +/- 20 mg/dL for concentrations predicted for plasma and whole blood, respectively.

CONCLUSION

Sampling factors rather than measurement accuracy limit the ability of capillary whole blood glucose measurements to predict venous concentrations.

Hypoxic inhibition of breathing in fetal sheep: relationship to brain adenosine concentrations

Because hypoxic inhibition of fetal breathing may be caused by a rise in central adenosine levels, the effects of O2 deficiency on fetal brain adenosine concentrations were determined at levels of hypoxia that inhibited fetal breathing. Under halothane anesthesia, the brains of fetal sheep (0.8 term) were implanted with guide cannulas exteriorized through a Silastic rubber window in the uterus and flank of the ewe. At least 4 days after surgery, a microdialysis probe was inserted into a cannula with the membrane tip placed in the rostral brain stem. During 1 h of isocapnic hypoxia, mean fetal arterial PO2 was reduced from 24.0 +/- 0.9 Torr (control) to 13 +/- 0.6 Torr and arterial pH fell progressively from 7.354 +/- 0.007 to 7.273 +/- 0.023. Hypoxia decreased the incidence of fetal breathing movements from 33 +/- 5.2 to 5 +/- 2.2 min/h, with a normal incidence (29 +/- 3.5 min/h) during the hour after arterial PO2 returned to control values. Adenosine concentrations in microdialysis perfusate under control conditions averaged approximately 35 nM, increased up to 2.3-fold during the hour of O2 deficiency, and fell toward control values when normoxia was restored. We conclude that fetal brain adenosine levels are increased at levels of O2 deficiency that inhibit fetal breathing, which are results consistent with a role for adenosine in hypoxic inhibition of fetal breathing.

Adenosine mediates hypoxic release of arginine vasopressin in fetal sheep

The effects of adenosine on plasma arginine vasopressin (AVP) concentrations were determined in chronically catheterized fetal sheep (> 0.8 term). Infusion of adenosine [0.35 +/- 0.01 (SE) mg.min-1.kg-1] into the inferior vena cava of six fetuses caused a transient fall in arterial PO2 (by approximately 3 Torr), a slight reduction in arterial pH, and a 5- to 6-mmHg decrease in diastolic pressure without significantly affecting systolic or mean arterial values. A lower rate of infusion (0.19 +/- 0.01 mg.min-1 x kg-1) in five fetuses had virtually no effect on arterial blood gases, pH, or arterial pressures. Both the low- and high-dose adenosine infusions significantly increased fetal plasma AVP concentrations (1.7 +/- 0.2 to 25 +/- 7 pg/ml and 1.6 +/- 0.1 to 54 +/- 8 pg/ml, respectively). Intravenous infusion of papaverine lowered fetal diastolic and mean arterial pressures by approximately 8 mmHg but had no significant effect on plasma levels of AVP. During an hour of isocapnic hypoxia (arterial PO2 12-13 Torr), fetal plasma AVP levels increased from 1.7 +/- 0.2 to 40 +/- 6 pg/ml. Intra-arterial infusion of the adenosine receptor antagonist 8-(p-sulfophenyl)-theophylline significantly blunted the hypoxia-induced rise in plasma AVP concentrations to a maximum mean level of 11 +/- 6 pg/ml. These results indicate that 1) adenosine causes a dose-dependent increase in plasma AVP concentrations and 2) a hypoxia-induced rise in fetal adenosine levels triggers vasopressin release.

Maternal and fetal cardiorespiratory responses to adenosine in sheep

OBJECTIVE

We determined the cardiorespiratory effects of maternal adenosine administration on the ewe and fetus.

STUDY DESIGN

Adenosine was infused intravenously to five pregnant ewes as graded (25 to 400 micrograms/min per kilogram) and constant (200 micrograms/min per kilogram) infusions and as a single injection (200 micrograms/kg). Heart rate, arterial pressure, and arterial blood gases and pH were monitored in the ewe and fetus; the data were analyzed with two-way analysis of variance with Duncan's test.

RESULTS

Graded adenosine infusion produced a dose-dependent rise in maternal heart rate and hemoglobin concentration and a fall in diastolic and mean arterial pressures, effects that were maintained during 1 hour of constant infusion. Single injections transiently lowered diastolic pressure and induced a biphasic change in heart rate consisting of a bradycardia followed by a tachycardia with a return to control values. Adenosine administration to the ewe did not affect maternal arterial blood gases and systolic pressure nor alter fetal heart rate, arterial pressure, or arterial blood gases.

CONCLUSION

Although adenosine causes cardiovascular changes in pregnant ewes, the effects are well tolerated and do not significantly affect the cardiorespiratory status of the fetus.

Cardiovascular responses to adenosine in fetal sheep: autonomic blockade

The mechanism by which adenosine increases heart rate was investigated in 21 chronically catheterized fetal sheep (> 0.8 term). Intra-arterial infusion of adenosine (0.16 mg.min-1.kg fetal wt-1) for 1 h significantly increased fetal heart rate within 5 min with maximum values of approximately 68 beats/min above the control mean of 163 +/- 8 beats/min. The average diastolic blood pressure was reduced only during the first 10 min of infusion, and the average systolic and mean arterial pressures were not significantly affected. Mean venous pressure rose by approximately 48% after 20 min of adenosine infusion, but all other measurements did not differ significantly from the control value. The mean hemoglobin concentration during the last 30 min of infusion was increased by approximately 8%. Plasma concentrations of norepinephrine and epinephrine were elevated only during the first 30 min of adenosine administration, to values as high as 2.3 and 5 times the respective control mean. Adenosine significantly increased mean fetal heart rate by about 15-20 beats/min in fetuses with autonomic ganglion blockade or combined cholinergic, alpha-, and beta-adrenergic receptor blockade. Intra-arterial infusion of CGS 21680C, an A2-adenosine receptor agonist, also produced a fetal tachycardia of approximately 86 beats/min above the control mean and increased intrinsic fetal heart rate by approximately 38 beats/min. It is concluded that approximately 75% of the positive chronotropic effects of adenosine are produced by A2-receptor stimulation of the autonomic nervous system and that approximately 25% of the rise in heart rate induced by adenosine may be caused by activation of A2-receptors in myocardium.

Adenosine in the treatment of maternal paroxysmal supraventricular tachycardia

Paroxysmal supraventricular tachycardia is the most common sustained cardiac arrhythmia in pregnant women. Because nearly 50% of these supraventricular tachyarrhythmias fail to respond to vagal maneuvers, other therapies are used, including electrocardioversion and pharmacologic agents. Propranolol, verapamil, and adenosine have Food and Drug Administration-approved labeling for acute termination of supraventricular tachycardia. Verapamil has been the most commonly used agent in the general population but it has several shortcomings, such as its potential to cause or exacerbate systemic hypotension, congestive heart failure, bradyarrhythmias, and ventricular fibrillation. In addition, verapamil readily crosses the placenta and has been shown to cause fetal bradycardia, heart block, depression of contractility, and hypotension. Adenosine has several advantages over verapamil, including rapid onset, brevity of side effects, theoretical safety, and probable lack of placental transfer. Adenosine ultimately may prove to be the preferred agent for termination of paroxysmal supraventricular tachycardia in the gravid woman.

Anemia up-regulates pontine A1 adenosine receptors in fetal sheep

A rise in central adenosine concentrations most likely triggers the inhibitory effects of acute hypoxia on fetal breathing movements. During prolonged O2 deficiency, the incidence of fetal breathing increases over time, an adaptation which may involve down-regulation of adenosine receptors. Therefore, isovolemic anemia was induced in chronically catheterized fetal sheep to determine the effects of acute O2 deprivation on the affinity of brainstem A1 adenosine receptors. Compared to control values, the mean hemoglobin concentration in 4 fetuses was lowered by 54% (to 3.7 +/- 0.4 g/dl) for 1 h and in 3 fetuses by 58% (to 3.8 +/- 0.6 g/dl) for 4 h. Mean preductal arterial pH during anemia was significantly reduced to values as low as 7.123 +/- 0.090, but mean paO2 and paCO2 were not significantly affected. The average incidence of fetal breathing movements was decreased by 80% during the first hour and by 50% during the fourth hour of anemia. In 3 fetuses with normal hemoglobin levels, about 32 +/- 6.0% of the A1 adenosine receptors in the brainstem were in the high affinity state. After 1 h of anemia, the percentage of high affinity receptors in the pons (but not medulla or midbrain) had significantly increased to 47 +/- 2.9%, but after 4 h of anemia all 3 brainstem regions had A1 receptor affinity within the range of control values. It is concluded that acute anemia induces a short-lived up-regulation of pontine A1 adenosine receptors, but anemia does not alter A1 receptor coupling in the midbrain where A1 receptors related to breathing inhibition may be located.

Fetal breathing, sleep state and cardiovascular adaptations to anaemia in sheep

1. In unanaesthetized fetal sheep (greater than 0.8 term) prolonged anaemia initially reduced the incidences of low-voltage electrocortical activity, rapid eye movements and breathing activity; but the incidence of each returned to normal within 4-7 h. 2. Anaemia induced a persistent rise in fetal heart rate and plasma concentrations of adrenaline, noradrenaline and cortisol. 3. After 16 h the fetal haematocrit was returned to normal. Isocapnic hypoxia induced less than 1 h later also inhibited eye and breathing activity. 4. After 1 h fetal arterial PO2 (Pa,O2) was returned to normal. This rise in O2 tension was associated with an elevation in the incidence of low-voltage electrocortical activity, eye movements and breathing. Breathing movements also occurred during high-voltage electrocortical activity. 5. It is concluded that the brain PO2 set-point for hypoxic inhibition adapts rapidly to alterations in O2-carrying capacity and is probably due to changes in the concentration and/or receptor affinity of a central neuromodulator. Secondly, a rise in brain PO2 at birth may contribute to the onset of continuous breathing.

Adenosine stimulates breathing in fetal sheep with brain stem section

Breathing responses to adenosine were determined in 12 chronically catheterized fetal sheep (greater than 0.8 term) in which hypoxic inhibition of breathing had been eliminated by brain stem section. The caudal extent of transection varied from the rostral midbrain to the pontomedullary junction. Isocapnic hypoxia [delta arterial PO2 (PaO2) of -12 Torr] doubled the incidence and depth of breathing activity and increased the incidence of eye movements. Intra-arterial infusion of adenosine (0.30 +/- 0.03 mg.min-1.kg fetal wt-1) increased the incidence and amplitude of breathing without affecting blood gases. Adenosine did not significantly alter the incidence of eye activity. Intra-arterial injection of oligomycin (120 +/- 26 micrograms/kg fetal wt), an inhibitor of mitochondrial oxidative phosphorylation, also stimulated breathing activity. In four fetuses with brain stem section, peripheral arterial chemodenervation blunted the stimulatory effects of hypoxia on breathing activity and abolished altogether the excitatory effects of adenosine. It is concluded that 1) hypoxia and adenosine likely inhibit breathing in normal fetuses by affecting similar areas of the brain stem and 2) in fetuses with brain section, hypoxic hyperpnea depends on peripheral and central mechanisms, whereas adenosine stimulates breathing via the peripheral arterial chemoreceptors.

Role of plasma adenosine in breathing responses to hypoxia in fetal sheep

The importance of plasma adenosine in hypoxic inhibition of breathing movements was determined in chronically catheterized fetal sheep (greater than 0.8 term). Preductal arterial blood for adenosine measurements was withdrawn using a double lumen catheter to mix blood entering the catheter with a solution to stop adenosine metabolism. In 6 fetuses, isocapnic hypoxia (delta PaO2 congruent to -10 Torr) increased the average plasma adenosine concentration from 1.1 +/- 0.2 (SEM) to 2.0 to +/- 0.4 microM. During hypoxia, plasma levels of adenosine were inversely related to preductal arterial O2 content (CaO2) with values ranging between 1.6 and 4.0 microM when CaO2 was less than 3 ml/dl. Hypoxia also significantly reduced the incidence of fetal breathing and rapid eye movements. In other experiments, adenosine (0.36 +/- 0.03 mg/min/kg) was infused for one hour into the inferior vena cava of 5 fetuses. During this infusion, mean plasma concentration of adenosine was 2.8 +/- 0.3 microM, a value about 2.5 times the control average. Adenosine also significantly reduced the incidence of low voltage electrocortical activity, rapid eye movements and breathing activity. We conclude that hypoxic inhibition of fetal breathing most likely arises from an increase in central adenosine production, although during severe O2 deprivation (CaO2 less than 3 ml/dl) blood-borne adenosine could also contribute.

Maturation of respiratory responses to graded hypoxia in rabbits

The respiratory effects of graded hypoxia were determined in 8 rabbits on postnatal days 1, 6 and 21. Ventilation was measured in the unanesthetized state by plethysmography. Graded hypoxia was produced by reducing the fraction of inspired O2 to 0.15 (mild hypoxia) for 15 min and then lowering it further to 0.10 (moderate hypoxia) for another 15 min. Mild hypoxia initially stimulated breathing to the same extent in all 3 groups; however, with moderate hypoxia, the percent increase in ventilation was greater for older rabbits. The rise in ventilation was due to an increase in tidal volume and frequency in 1- and 21-day-old rabbits, and it was almost entirely the result of changes in frequency in 6-day-old rabbits. After 2-3 min of hypoxia (mild or moderate), a decline in ventilation was observed in all 3 groups. This reduction of respiration was greater in younger animals and with moderate hypoxia. Decreases in frequency and tidal volume contributed significantly to this fall in ventilation for 1- and 2-day-old rabbits. However, the fall in ventilation for 6-day-old pups occurred almost entirely by changes in tidal volume. It is concluded that the magnitude of phase 1 (increased ventilation) and phase 2 (decreased ventilation) responses to hypoxia depend upon the level of hypoxia and the age of the rabbit.

Fetal breathing and cardiovascular responses to graded methemoglobinemia in sheep

Graded methemoglobinemia (MetHb) was produced in unanesthetized fetal sheep to determine the effects on brain oxygenation. MetHb was induced by infusing methemoglobin-containing erythrocytes in exchange for fetal blood. During the hour after MetHb was established, fetal methemoglobin concentrations averaged 1.23 +/- 0.12 (mild MetHb), 1.71 +/- 0.13 (moderate MetHb), and 2.27 +/- 0.17 g/dl (severe MetHb). MetHb reduced mean arterial O2 content by approximately 19 (mild MetHb), 29 (moderate MetHb), and 39% (severe MetHb). The average preductal arterial PO2 fell by 1.6 (-7%), 2.8 (-11%), and 4.0 Torr (-16%) for mild, moderate, and severe MetHb, respectively. Fetal heart rate increased significantly during mild and moderate MetHb, and mean arterial pressure fell slightly during moderate and severe MetHb. The incidences of fetal breathing and eye movements were reduced in a dose-dependent manner when the calculated brain end-capillary PO2 was less than 14 Torr. We conclude that: 1) the effective capillary PO2 in the fetal brain can be significantly reduced by increasing the distance between non-methemoglobin-laden erythrocytes in capillaries and 2) hypoxic inhibition of fetal breathing probably arises from discrete areas of the brain having a PO2 less than 3 Torr.

Pregnancy and congenital heart disease

Congenital heart disease as a complicating factor in pregnancy has assumed increasing clinical importance because improved techniques of surgical repair have resulted in a larger proportion of affected women living to the reproductive age. The most serious forms are those associated with pulmonary hypertension (such as the Eisenmenger syndrome), which carry a prohibitively high risk of maternal death. Complex forms of cyanotic heart disease, of which the commonest is the tetralogy of Fallot, are only slightly less dangerous. It has recently been recognized that children born to women with congenital heart disease are at increased risk of having cardiac defects; fetal echocardiography is therefore an important diagnostic test. Optimal care of the pregnant woman with congenital heart disease is best provided by a team consisting of internist-cardiologist, obstetrician-perinatologist, obstetric anesthesiologist, and ultrasonographer-echocardiographer.

Fetal breathing, sleep state, and cardiovascular responses to adenosine in sheep

The possibility that adenosine mediates hypoxic inhibition of fetal breathing and eye movements was tested in nine chronically catheterized fetal sheep (0.8 term). Intracarotid infusion of adenosine (0.25 +/- 0.03 mg.min-1.kg-1) for 1 h to the fetus increased heart rate and hemoglobin concentration but did not significantly affect mean arterial pressure or blood gases. As with hypoxia, adenosine decreased the incidence of rapid eye movements by 55% and the incidence of breathing by 77% without significantly affecting the incidence of low-voltage electrocortical activity. However, with longer (9 h) administration, the incidence of breathing and eye movements returned to normal during the adenosine infusion. Intravenous infusion of theophylline, an adenosine receptor antagonist, prevented most of the reduction in the incidence of breathing and eye movements normally seen during severe hypoxia (delta arterial PO2 = -10 Torr). It is concluded that 1) adenosine likely depresses fetal breathing and eye movements during hypoxia and 2) downregulation of adenosine receptors may contribute to the adaptation of breathing and eye movements during prolonged hypoxia.

Effects of regular and decaffeinated coffee on fetal breathing and heart rate

The effects of maternal consumption of regular or decaffeinated coffee on the fetus were determined in eight pregnant women at 32 to 36 weeks of gestation. This was a single-blind crossover study in which two cups of caffeinated or decaffeinated coffee were consumed after an overnight fast. The total maternal caffeine ingested was 454 +/- 4 mg for regular coffee and 12 +/- 0.4 mg for decaffeinated coffee. Maternal consumption of regular coffee was associated with a twofold increase in the incidence of fetal breathing activity and a significant fall in baseline fetal heart rate. Decaffeinated coffee also increased the incidence of fetal breathing activity and produced a slight reduction in fetal heart rate. These results indicate that maternal consumption of regular and decaffeinated coffee can stimulate fetal breathing. Moreover, these results suggest that caffeinated coffee can produce baseline shifts in fetal heart rate.