Decreased neuroinflammation correlates to higher vagus nerve activity fluctuations in near-term ovine fetuses: a case for the afferent cholinergic anti-inflammatory pathway?

BACKGROUND: Neuroinflammation in utero may contribute to brain injury resulting in life-long neurological disabilities. The pivotal role of the efferent cholinergic anti-inflammatory pathway (CAP) in controlling inflammation, e.g., by inhibiting the HMGB1 release, via the macrophages' α7 nicotinic acetylcholine receptor (α7nAChR) has been described in adults, but its importance in the fetus is unknown. Moreover, it is unknown whether CAP may also exert anti-inflammatory effects on the brain via the anatomically predominant afferent component of the vagus nerve. METHODS: We measured microglial activation in the ovine fetal brain near term 24 h after the umbilical cord occlusions mimicking human labor versus controls (no occlusions) by quantifying HMGB1 nucleus-to-cytosol translocation in the Iba1+ and α7nAChR+ microglia. Based on multiple clinical studies in adults and our own work in fetal autonomic nervous system, we gauged the degree of CAP activity in vivo using heart rate variability measure RMSSD that reflects fluctuations in vagus nerve activity. RESULTS: RMSSD correlated to corresponding plasma IL-1ß levels at R = 0.57 (p = 0.02, n = 17) and to white matter microglia cell counts at R = -0.89 (p = 0.03). The insult increased the HMGB1 translocation in α7nAChR+ microglia in a brain region-dependent manner (p < 0.001). In parallel, RMSSD at 1 h post insult correlated with cytosolic HMGB1 of thalamic microglia (R = -0.94, p = 0.005), and RMSSD at pH nadir correlated with microglial α7nAChR in the white matter (R = 0.83, p = 0.04). Overall, higher RMSSD values correlated with lower HMGB1 translocation and higher α7nAChR intensity per area in a brain region-specific manner. CONCLUSIONS: Afferent fetal CAP may translate increased vagal cholinergic signaling into suppression of cerebral inflammation in response to near-term hypoxic acidemia as might occur during labor. Our findings suggest a new control mechanism of fetal neuroinflammation via the vagus nerve, providing novel possibilities for its non-invasive monitoring in utero and for targeted treatment.

Placental 11beta-hydroxysteroid dehydrogenase type 2 is reduced in pregnancies complicated with idiopathic intrauterine growth Restriction: evidence that this is associated with an attenuated ratio of cortisone to cortisol in the umbilical artery.

The placental 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) serves as a functional barrier to protect the fetus from excessive exposure to high levels of maternal cortisol. There is evidence that placental 11beta-HSD2 is reduced in pregnancies complicated with intrauterine growth restriction (IUGR), but the relationship between the two is uncertain owing to other maternal complications often associated with this pathological condition of pregnancy. To gain insight into the role of placental 11beta-HSD2 in the pathogenesis of IUGR, we studied variations in the activity and expression of this important enzyme as well as its functional indicator, the ratio of cortisone to cortisol in umbilical cord blood, in a cohort of 12 term deliveries complicated with idiopathic IUGR and 12 term controls. We showed that both placental 11beta-HSD2 activity and mRNA were reduced in IUGR. This was accompanied by a decrease in the ratio of cortisone to cortisol in the umbilical artery, suggesting that not only placental but also fetal 11beta-HSD2 activity may be compromised in idiopathic IUGR. Given that we previously identified the nuclear receptor PPARdelta as a potent suppressor of placental 11beta-HSD2, we also tested but found no evidence to support the hypothesis that placental PPARdelta expression is increased in IUGR thereby contributing to the molecular mechanisms that underlie the attenuated placental 11beta-HSD2. Taken together, our present findings provide evidence suggesting a role for an attenuated placental as well as fetal 11beta-HSD2 in the pathogenesis of IUGR.

The effect of intermittent umbilical cord occlusion on insulin-like growth factors and their binding proteins in preterm and near-term ovine fetuses.

Intermittent umbilical cord compression with resultant fetal hypoxia can have a negative impact on fetal growth and development. Insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) are the most important regulators of fetal growth. In preterm (107-108 days of gestation) and near-term (128-131 days of gestation) ovine fetuses, we have determined the effect of intermittent umbilical cord occlusion (UCO) over a period of 4 days on the profile and expression of IGFs and IGFBPs. In experimental group animals (preterm n=7; near term n=7) UCOs were carried out by complete inflation of an occluder cuff (duration 90 s) every 30 min for 3-5 h each day, while control fetuses (preterm n=7; near term n=7) received no UCOs. Ewes were euthanized at the end of day 4, and fetal heart, lung, kidney, liver, skeletal muscle and placenta were collected. During UCOs, PO(2! ) fell (by approximately 13 mmHg), pH fell (by approximately 0.05) and PCO(2) increased (by approximately 7 mmHg), and changed to a similar extent in both preterm and near-term groups. In both preterm and near-term groups, there was no difference in fetal body or organ weight between UCO and control fetuses. No significant changes were observed in plasma IGF-I and -II concentrations or IGFBP-1, -2, -3 or -4 levels throughout the 4-day study at either gestational age. In the preterm group UCO fetuses, IGF-II mRNA (1.2-6.0 kb) levels were lower in fetal lung (33%, P<0.05), heart (54%, P<0.01) and skeletal muscle (29%, P<0.05), but there were no differences in IGF-I mRNA levels (7.3 kb); IGFBP-2 mRNA (1.5 kb) levels were lower in the right lobe of the liver (42%, P<0.05) and kidney (22%, P<0.01), but hig! her in the heart (72%, P<0.01), while IGFBP-4 (2.4 kb) levels were lower in skeletal muscle (21%, P<0.01). In the near-term group UCO fetuses, IGFBP-2 mRNA levels were greater in the placenta (39%, P<0.05). Thus, intermittent UCO as studied has a greater effect on the expression of genes encoding certain peptides of the fetal IGF system in selected tissues in preterm fetuses than that in near-term fetuses. Altered IGFBP-2 mRNA levels with reduced IGF-II mRNA levels in selected tissues may mediate changes in growth and/or differentiation that might become apparent if the length of the UCO study were extended.

Initiation of pulmonary gas exchange by fetal sheep in utero.

The role of umbilical cord occlusion in the initiation of breathing at birth was investigated using unanesthetized fetal sheep that were provided with access to a tracheal supply of hyperoxic air. Near-term fetuses were studied in utero to eliminate extraneous sensory stimuli. Gasping movements began 1.4 +/- 0.1 min after cord occlusion. Breathing was irregular for several minutes before continuous breathing (greater than or equal to 40 min-1) began 6 +/- 1 min after cord occlusion (n = 10). Arterial PO2 rose significantly from 18 +/- 2 mmHg before occlusion and was 115 +/- 15 mmHg immediately before cord release at 15 or 30 min. Breathing continued even during high-voltage electrocortical activity. Cord release caused the breathing rate to decrease from 77 +/- 13 min-1 during the last 5 min of cord occlusion to 5 +/- 3 min-1 10 min after cord release (P less than 0.002; n = 7). Results indicate the change from placental to lung gas exchange can occur in the absence of sensory and thermal changes normally present at birth and that the transition is reversible.

The effects of 'sleep promoting agents' on behavioural state in the ovine fetus.

Fetal behavioural states, with similarities to adult sleep states, exist in both the human and ovine fetus near term. The purpose of the present study was to determine the effects of intracerebral administration of pharmacologic agents, known to affect sleep states in the adult, on fetal behavioural states and physiologic correlates using the chronically catheterized ovine fetus near term. Each drug was infused into either the cisterna magna or lateral ventricle for 90 min in one of two doses. Carbachol (1.35 x 10(-5) and 4.25 x 10(-6) M) led to an increase in low-voltage ECOG, eye movement and FBM activities, while scopolamine (4.68 x 10(-4) and 1.56 x 10(-4) M) led to a decrease in low-voltage ECOG and eye movement activity with an increase in high-voltage ECOG activity. L-5-Hydroxytryptophan (5-HTP) (2.04 x 10(-3) and 6.81 x 10(-4) M) infusion led to an increase in FBM, while VIP (3.00 x 10(-7) and 1.00 x 10(-7) M) infusion had no effect on fetal behavioural state parameters. Study results indicate that fetal behavioural states can be altered pharmacologically and in a manner similar to that seen in the adult but with notable differences that may relate to species, developmental or dose-response issues.

Regional brain blood flow in the ovine fetus during transition to the low-voltage electrocortical state.

Sequential changes in cerebral blood flow and regional distribution were studied in nine chronically catheterized fetal sheep during the transition to the low-voltage ECOG (REM) state to determine the time course for blood flow change within the brain and whether executive centres for REM state generation might thus be identified. Blood flows were measured during the first, second and third minutes after the transition to the low-voltage ECOG state and during the third minute of the subsequent high-voltage ECOG (NREM) state using the radioactive labelled microsphere technique. Blood flow to the brain was increased during the low-voltage REM state when compared to that of the high-voltage NREM state, with the increase evident when measured during the first minute after the state transition and with no sequential change thereafter. Regional blood flow increases during the low-voltage state were greatest to those areas variously associated with the generation of REM state activity, but were again remarkably stable through the first 3 minutes after the state transition. This rapid increase in blood flow within the brain and the regional hierarchy for such, supports the participation of multiple anatomical areas which are highly integrated and act in concert to give rise to what is known as the REM state.

Sagittal sinus blood flow in the ovine fetus as a continuous measure of cerebral blood flow: relationship to behavioural state activity.

Superior sagittal sinus blood flow (Q(ss)) was studied over a 6-h period in nine chronically catheterized fetal sheep as a continuous measure of cerebral blood flow to determine the change in blood flow values and in measures of blood flow variability in relation to behavioural state activity. Mean Q(ss) was increased during the low voltage (LV)/rapid eye movement (REM) state compared to the high voltage (HV)/NREM state by approximately 25%, and was further increased during periods of LV/REM with fetal breathing movements. The increase in Q(ss) was abrupt and began at the transition to LV/REM, with the rate of change 2-fold greater than that during transition to HV/NREM, where the decrease in Q(ss) was gradual and began prior to the evident state change. Q(ss) showed considerable fluctuation, which tended to be greater during the HV/NREM state compared to the LV/REM state when analyzed using measures of longer term variability. Q(ss) thus provides for a continuous measure of cerebral blood flow in the ovine fetus, with the approximately 25% increase with change from the HV/NREM to LV/REM state similar to that previously reported using radioactive microspheres. The abrupt increase in Q(ss) at the transition to LV/REM versus the gradual decrease in Q(ss) before transition to HV/NREM would suggest that the state-related change in brain blood flow is better linked to the presence of the LV electrocorticogram and favours its active generation.

The effect of behavioral state on fetal metabolism and blood flow circulation.

As in postnatal life, behavioral states when evident in utero are also seen to influence the metabolic activity and/or circulation of several organ systems if not the global metabolic and circulatory activity of the fetus. In some instances this effect is organ specific as in the increased metabolic activity of the brain during the fetal REM state, which may account for the prominence of this state through the perinatal period and contribute to the brain's growth and development at this time. Generalized metabolic and circulatory effects may also be seen as associated with state-related changes in fetal biophysical activity or circulating vasoactive substances. Although the exact functions of sleep and sleep states are not yet known, their influence on the metabolic and circulatory activity of organ systems is seen to onset in early life, suggesting that a need for such may be just as important during early development as in later life.

Effects of hypoxemia on 11 beta-hydroxysteroid dehydrogenase types 1 and 2 gene expression in preterm fetal sheep.

OBJECTIVE: To examine the effect of sustained hypoxia on the expression of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) type 1 and 2 genes in preterm fetal sheep. METHODS: Fetal liver and kidney as well as placental tissues were collected at days 111-113 of gestation (term = 145 days) after 8 hours of sustained hypoxemia induced by lowering the maternal inspired oxygen (n = 7) or after 8 hours of normoxia to serve as controls (n = 5). Changes in the levels of 11 beta-HSD1 and 11 beta-HSD2 mRNA were determined by Northern blot analysis using ovine 11 beta-HSD types 1 and 2 cDNAs as probes. Levels of 11 beta-HSD2 activity were determined by a standard radiometric conversion assay. RESULTS: In hypoxic fetuses, there was a tendency for a decrease (P = .08) in levels of 11 beta-HSD2 mRNA in the kidney. This decrease was correlated significantly with the degree of associated fetal acidemia (P < .01). However, there were no corresponding changes in the level of renal 11 beta-HSD2 enzyme activity, indicating that changes in 11 beta-HSD2 mRNA were unlikely carried through to 11 beta-HSD2 protein. In contrast levels of 11 beta-HSD1 mRNA in the placenta and fetal liver were unchanged after sustained hypoxia. CONCLUSION: These results demonstrate that fetal hypoxemia-induced acidosis selectively down-regulates 11 beta-HSD2 mRNA expression in the preterm fetal sheep kidney. This may provide a further mechanism whereby fetal acidosis alters developmental processes by regulating the bioavailability of glucocorticoids in specific fetal organs through altered local expression of 11 beta-HSD enzymes.

Tissue DNA synthesis in the preterm ovine fetus following 8 hours of sustained hypoxemia.

OBJECTIVE: Protein synthesis is significantly decreased in the near-term ovine fetus in response to induced hypoxemia of several hours' duration. We therefore sought to determine the extent to which DNA synthesis rates as an index of tissue mitotic activity are also affected by similarly induced compromises in fetal oxygenation. METHODS: Fetal sheep were studied at 0.75 of gestation during a normoxic control period and an 8-hour experimental period of either sustained hypoxemia induced by lowering maternal inspired oxygen concentration of 11-8% (hypoxia group, n = 7) or continued exposure to room air (control group, n = 5). To estimate DNA synthesis rate, [3H]-thymidine (1 mCi/kg) was injected intravenously into each fetus at the beginning of the experimental period. RESULTS: Sustained hypoxemia with a reduction in fetal arterial O2 content from (mean +/- standard error of the mean) 4.3 +/- 0.1 to 1.5 +/- 0.1 mmol/L by the end of study resulted in a variable degree of fetal acidemia, 7.26 +/- 0.03 (range from 7.41 to 7.10), which was entirely metabolic in nature. CONCLUSION: The DNA synthesis rates of most tissues were not significantly changed by the 8 hours of sustained hypoxemia, suggesting that restrictions in protein synthesis in response to fetal hypoxia are initially due to a differential effect on nonmitotic synthetic processes at this stage of development. However, selective decreases in the DNA synthesis rates of the hippocampus (approximately 50%, P < .01), adrenals (approximately 48%, P < .05), and left and right myocardial ventricles (approximately 42% and 27%, respectively, P = .08) were evident which may reflect altered mitotic activity in response to tissue related changes in energy expenditure.

Cardiovascular and metabolic responses to intermittent umbilical cord occlusion in the preterm ovine fetus.

OBJECTIVE: To determine the cardiovascular and metabolic responses to umbilical cord occlusion in the preterm ovine fetus and the impact of repetitive intermittent insults over a 4-day period. METHODS: Repetitive umbilical cord occlusions (experimental group, n = 7; control group, n = 7) were performed daily (112-115 days' gestation, term = 147 days). Mean arterial pressure (MAP), fetal heart rate (FHR), and FHR variation were monitored, and arterial blood was sampled at predetermined intervals. RESULTS: During umbilical cord occlusions, arterial oxygen pressure (PaO2) (approximately 17 mmHg) and glucose (approximately 0.3) millimoles per liter (mmol/L) fell and arterial carbon dioxide pressure (approximately 8 mmHg) rose (P < .01) to a similar extent on days 1 and 4. Umbilical cord occlusion produced a rise in lactate over the course of successive umbilical cord occlusions each day, the magnitude of which tended to be reduced by day 4 (0.3 +/- 0.1 versus 0.6 +/- 0.1 mmol/L). Control hour FHR and MAP were unaltered over the 4 days, but the delta (delta) FHR to delta PaO2 ratio during umbilical cord occlusions was less on day 4 than on day 1 (6.0 +/- 0.4 versus 10.9 +/- 1.5 beats per minute/mmHg; P < .01). During occlusion hours, high FHR variation episodes, as a measure of fetal activity, were reduced (14.6 +/- 1.5 versus 4.2 +/- 1.3 min/h; P < .01), whereas the reduction in short-term (7.4 +/- 0.7 to 5.8 +/- 0.6 milliseconds; P < .05) and long-term (34.9 +/- 2.7 to 30.0 +/- 0.6 milliseconds; P < .05) FHR variation reached significance only on day 4. CONCLUSION: The increase in lactate and reduced high-FHR variation episodes over successive umbilical cord occlusions may affect fetal growth and development. Furthermore, repeated umbilical cord occlusions over several days alter the preterm FHR response to subsequent stresses, suggesting an altered chemoreflex response.

Activation of the hypothalamic-pituitary-adrenal axis with repetitive umbilical cord occlusion in the preterm ovine fetus.

OBJECTIVE: To determine whether repeated hypoxic insults with umbilical cord occlusion over 4 days will lead to activation of the hypothalamic-pituitary-adrenal (HPA) axis altered adrenocortical responsiveness in the preterm ovine fetus. METHODS: Umbilical cord occlusions of 90 seconds duration were performed every 30 minutes for 3 to 5 hours each day (experimental group n = 7, control group n = 7; at 112-116 days' gestation, term = 147 days). Arterial blood was sampled at predetermined times for blood gases and pH, plasma ACTH, and cortisol. Pituitary proopiomelanocortin (POMC) and glucocorticoid receptor (GR) mRNA also were localized and quantified by in situ hybridization. RESULTS: During umbilical cord occlusions fetal arterial oxygen pressure (approximately 17 mmHg) and pH (approximately 0.05) decreased, and carbon dioxide pressure increased (approximately 8 mmHg) as measured on days 1 and 4, but with no cumulative blood gas or pH change over successive occlusions for any of the 4 study days. Plasma ACTH increased, as measured after cord occlusion and over the course of successive cord occlusions on days 1 and 4, and returned to control values by the next day. The cumulative increase in ACTH was much less on day 4 than day 1 (15 +/- 3 compared with 101 +/- 25 pg/mL, P <.05). Plasma cortisol increased, as measured after cord occlusion and over the course of successive cord occlusions on day 4 only (2.7 +/- 0.4 to 4. 7 +/- 0.3 ng/mL, P <.05). POMC mRNA increased 2.5-fold in the pars distalis of the pituitaries from cord occlusion compared to control fetuses, but was unchanged in the pars intermedia. GR mRNA, which was detected in the pars distalis only, was unaltered. CONCLUSION: Repetitive umbilical cord occlusion in the preterm ovine fetus resulted in the activation of the HPA axis, with increased adrenocortical responsiveness over time, and involved differential regulation of POMC mRNA expression in the pars distalis and pars intermedia of the pituitary, but with no change in GR.

Intermittent umbilical cord occlusion in the ovine fetus: effects on blood glucose, insulin, and glucagon and on pancreatic development.

OBJECTIVE: To determine whether repetitive umbilical cord occlusion resulting in fetal hypoxemia but not cumulative acidosis also affects fetal glucose levels and the levels of the regulatory hormones insulin and glucagon, by altering glucose delivery and with repetitive insults by inducing fetal glucose production, thus possibly affecting pancreatic development. METHODS: Fifteen chronically catheterized fetal sheep were studied over 21 days. Umbilical cord occlusions (UCOs) (duration 90 seconds) were performed every 30 minutes for 3-4 hours each day. Fetal arterial blood was sampled at predetermined times on days 1, 9, and 18 for blood gases, pH, glucose, lactate, insulin, and glucagon. When animals were sacrificed, fetal pancreatic tissues were collected for insulin immunostaining. RESULTS: Blood glucose decreased acutely with each UCO but showed a cumulative increase of approximately 30% over the course of each sampling day. Although plasma insulin levels also increased over the course of sampling on days 9 and 18, plasma glucagon levels remained unchanged throughout the study. The percentage of pancreatic islet cells immunopositive for insulin, which averaged 67%, was also unchanged in experimental compared with control animals. CONCLUSION: Umbilical cord occlusion during the latter part of pregnancy, which caused severe but limited hypoxemia, also resulted in acute decreases in blood glucose levels because of reduced exogenous glucose delivery and a cumulative increase in glucose in response to repetitive insults, possibly by inducing fetal glucose production, enhancing glucose delivery, or both. However, repetitive UCO as studied had minimal effect on plasma insulin levels and no effect on glucagon levels or on pancreatic immunostaining for insulin, and thus had no evident effect on pancreatic development.

Effects of sustained hypoxaemia with 72 hours recovery on 11beta-hydroxysteroid dehydrogenase types 1 and 2 gene expression in near-term fetal sheep.

The study examined the effects of 8 h sustained hypoxaemia, with 72 h recovery, on the expression of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) types 1 and 2 in near-term fetal sheep. Placental tissue and fetal liver and kidney were collected at Days 135-138 gestation 72 h after 8 h sustained hypoxaemia induced by lowering maternal inspired oxygen with (n = 9) and without (n = 6) metabolic acidosis or after 8 h normoxia (n = 6). In hypoxic fetuses with metabolic acidosis, a significant increase in the level of 11beta-HSD2 mRNA in the kidney compared with controls was correlated significantly with degree of associated fetal acidaemia, but there were no corresponding increases in the tissue level of 11beta-HSD2 activity. Hence, a time lag may exist between the mRNA and activity. Alternatively, the translation of 11beta-HSD2 mRNA may be inhibited. In contrast, levels of 11beta-HSD1 mRNA in the placenta and fetal liver were unchanged 72 h after sustained hypoxaemia. These results indicate that sustained fetal hypoxaemia with metabolic acidosis selectively up-regulates 11beta-HSD2 mRNA expression in the near-term fetal sheep kidney. This may be a re-bound effect at 72 h following an initial down-regulation as observed in a previous study.

Nuchal cord evident at birth impacts on fetal size relative to that of the placenta.

We sought to determine whether umbilical cord complications, as evidenced by a nuchal cord at the time of birth, affects birth weight, placental weight and, therefore, the birth to placental weight ratio as a mechanism whereby fetal and placental growth may be differentially affected. The computerized perinatal database of St. Joseph's Health Centre, London, Ontario, was used to obtain the birth weight, placental weight, umbilical cord gases, and nuchal cord status, for all term singleton liveborn infants between January, 1991 and December, 1994. The effect of no nuchal cord versus nuchal cord on birth weight, placental weight, and the birth to placental weight ratio was determined, along with the interactive effects of gestational age and umbilical cord gases, and the 'dose response' effect of the number of cord encirclements. Infants with the cord around the neck were smaller (P < 0.001), their placentas larger (P = 0.001), and their birth to placenta weight ratio also smaller (P < 0.001), with a 'dose response' relationship apparent as these effects were greater in those infants with more than one cord encirclement. Although gestational age and umbilical cord veno-arterial PO2 and PCO2 differences were also found to impact on birth weight, placental weight, and the birth to placental weight ratio, these effects were independent of the effect of nuchal cord complications. Umbilical cord complications is evidenced by a nuchal cord at the time of birth, are associated with a decrease in fetal size relative to that of the placenta, although this is likely to be of little biological significance for most nuchal cord infants.

Fetal adaptive responses to asphyxia.

The fetal environment is thus well suited for normal growth and development with oxygen availability exceeding oxidative needs. With impairments in blood gas exchange this excess oxygen acts as a "margin of safety," providing for the maintenance of oxidative metabolism through increases in fractional O2 extraction, although with resultant fetal hypoxemia. Increases in blood O2 capacity and redistribution of cardiac output in response to this hypoxemia further protect fetal oxygenation. Additional adaptive mechanisms involve a decrease in energy-consuming processes, including growth restriction, decreasing fetal movements, and behavioral state alterations. Although protective in so far as essential metabolic functions are maintained, pathologic change may occur as the "oxygen margin of safety" becomes limited or energy-conserving measures give rise to abnormal growth and development.

Increased collagen deposition in the heart of chronically hypoxic ovine fetuses.

This study determined the effect of chronic intrauterine hypoxia on collagen deposition in the fetal sheep heart. Moderate or severe hypoxia was induced by placental embolization in chronically catheterized fetal sheep for 15 days starting at gestational day 116 ± 2 (term ∼147 days). The fetal right and left ventricle were evaluated for collagen content using a Sirius red dye and for changes in signaling components of pathways involved in collagen synthesis and remodeling using quantitative polymerase chain reaction and Western blot. In severely hypoxic fetuses (n = 6), there was a two-fold increase (P < 0.05) in the percentage staining for collagen in the right ventricle, compared with control (n = 6), whereas collagen content was not altered in the moderate group (n = 4). Procollagen I and III mRNA levels were increased in the right ventricle, two-fold (P < 0.05) and three-fold (P < 0.05), respectively, in the severe group relative to control. These changes were paralleled by a two-fold increase (P < 0.05) in mRNA levels of the pro-fibrotic cytokine, transforming growth factor ß (TGF-ß1), in the right ventricle. In the right ventricle, the mRNA levels of matrix metalloproteinase 2 (MMP-2) and its activator, membrane-type MMP (MTI-MMP) were increased five-fold (P = 0.06) and three-fold (P < 0.05), respectively, relative to control. Protein levels of TGF-ß were increased in the left ventricle (P < 0.05). Thus, up-regulated collagen synthesis leading to increased collagen content occurs in the chronically hypoxic fetal heart and may contribute to the right ventricular diastolic and systolic dysfunction reported in human intrauterine growth restriction fetuses.

Neonatal outcomes are associated with latency after preterm premature rupture of membranes.

OBJECTIVE: To determine factors associated with latency time to birth after preterm premature rupture of membranes (PPROM) and the impact on neonatal outcomes. STUDY DESIGN: Data on singleton pregnancies with PPROM (n=1535 infants) were prospectively collected in a computerized perinatal/neonatal database at a tertiary care perinatal center. Latency was characterized as ≤72h versus >72 h after PPROM. RESULT: The percentage of women with latency to birth >72 h decreased from 67% in very preterm (gestational age (GA) 25 to 28 weeks) to 10% in late preterm women (GA 33 to 36 weeks). PPROM women with latency ≤72 h were more likely to have pregnancy-induced hypertension and birth weight <3%; PPROM women with latency >72 h were more likely to have received steroids and develop clinical chorioamnionitis. PPROM <32 weeks GA with latency ≤72 h was associated with a two-fold higher incidence of severe neonatal morbidity, while PPROM between 29 to 34 weeks GA and latency ≤72 h was associated with a higher incidence of moderate neonatal morbidity. CONCLUSION: A latency period >72 h was associated with a decreased incidence of adverse neonatal outcomes up to 32 weeks GA for severe and 34 weeks GA for moderate morbidity indices.

The fetal brain: metabolic and circulatory responses to asphyxia.

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

Metabolic and circulatory adaptations to chronic hypoxia in the fetus.

When oxygenation is compromised the fetus is capable of a number of adaptive responses, both protective and potentially pathologic, which can be categorized as those affecting fetal metabolism and those affecting fetal oxygen transport. However, both the extent and the duration of the impairment in oxygenation will bear on these adaptive responses. While fetal O2 extraction is increased when oxygenation is acutely compromised thus maintaining O2 consumption, with chronic hypoxemia there is a decrease in O2 consumption paralleling that in O2 delivery and contributed to by the resultant fall-off in growth and alterations in behavioural activity. While a redistribution of blood flow to vital organs continues to be evident, this will be less pronounced than that seen with acute hypoxemia reflecting diminished hormonal changes, underlying metabolic alterations, and the extent to which fetal blood gases are normalized. Much of this information is based on experimental data using unanesthetized fetal sheep with chronic catheterization; however, clinical outcome data and the use of investigative techniques including ultrasound scanning and cordocentesis have supported the relevance of this experimental data to the human situation.