Blood volume reduction due to rapid plasma loss after birth in preterm piglets.

BACKGROUND: Understanding changes in blood volume after preterm birth is critical to preventing cardiovascular deterioration in preterm infants. The aims were to determine if blood volume is higher in preterm than term piglets and if blood volume changes in the hours after birth. METHODS: Paired blood volume measurements were conducted in preterm piglets (98/115d gestation, ~28wk gestation infant) at 0.5-5 h (n = 12), 0.5-9 h (n = 44) and 5-11 h (n = 7) after birth, and in a term cohort at 0.5-9 h (n = 40) while under intensive care. RESULTS: At 30 min after birth, blood volume was significantly lower in preterm piglets compared to term piglets. By 9 h after birth, blood volume had reduced by 18% in preterm piglets and 13% in term piglets. By 5-9 h after birth, preterm piglets had significantly lower blood volumes than at term (61 ± 10 vs. 76 ± 11 mL/kg). CONCLUSIONS: In contrast to clinical resources, preterm piglets have a lower blood volume than at term. Substantial reductions in blood volume after birth leave some preterm piglets hypovolemic. If this also occurs in preterm infants, this may have important clinical consequences. Modern studies of blood volume changes after birth are essential for improving preterm outcomes. IMPACT: Preterm piglets do not have a higher blood volume than their term counterparts, in contrast to current clinical estimates. Rapid reduction in blood volume after birth leads to hypovolemia in some preterm piglets. There is a critical need to understand blood volume changes after birth in preterm infants in order to improve clinical management of blood volume.

Red cell infusion but not saline is effective for volume expansion in preterm piglets.

BACKGROUND: A common first-line treatment for supporting cardiovascular function in preterm infants is volume expansion using saline, but this does not improve outcomes. This study aimed to determine if volume expansion with saline increases blood volume, blood pressure and cerebral oxygenation; and if volume expansion with packed red blood cells (RBC) is more effective. We hypothesized that RBC infusion is more effective than saline for increasing blood volume and maintaining cardiovascular function and cerebral oxygenation. METHODS: Five groups of preterm piglets (98/115d gestation) were infused with saline (10 or 20 mL/kg) or RBC (10 or 20 mL/kg) or no treatment. Blood volume, blood pressure, central venous pressure, heart rate, carotid flow, cerebral oxygenation, arterial pH, base excess, and lactate levels were assessed for 6 h after treatment started. RESULTS: Both RBC groups had significant increases in blood volume, and improved measures of cardiovascular function, cerebral oxygenation and metabolic acidosis. Saline infusion did not increase blood volume or measures of cardiovascular function, cerebral oxygenation or metabolic acidosis. CONCLUSIONS: The results suggest that the deteriorating cardiovascular function in the hours after birth in preterm piglets, and possibly in premature babies, may be reversed or halted by more effective support of blood volume. IMPACT: Blood volume decreases after birth in preterm piglets and this decrease is associated with deteriorating cardiovascular function and cerebral oxygenation. Infusion of saline does not increase blood volume nor prevent deterioration in cardiovascular function. Infusion of packed red blood cells results in an increase in blood volume and improvements in cardiovascular function and cerebral oxygenation. Deteriorating cardiovascular function in the hours after birth in preterm piglets, and possibly in human preterm neonates, may be reversed or halted by more effective support of blood volume.

Expression of TRPM6 and TRPM7 in the preterm piglet heart.

Preterm infants are at increased risk of death and disability, and cardiovascular instability after birth is a contributing factor. Immaturity of calcium handling in the preterm heart may limit myocardial contractility and cardiac output. Two transmembrane cation channels, TRPM6 and TRPM7, may regulate intracellular cardiac calcium in the neonatal period. The aim of this study was to determine TRPM6 and TRPM7 mRNA expression in piglet hearts in late gestation, and the effects of sex, maternal glucocorticoids, and the transition to extrauterine life. Left and right ventricular tissue was collected at a range of gestational ages from cesarean delivered piglets at birth and at 6 h old. Additional groups included piglets exposed to maternal glucocorticoid treatment and spontaneously born term piglets at 12-24 h old. TRPM6 and TRPM7 mRNA expression was measured using RT-qPCR. Males had significantly lower TRPM7 expression in the left ventricle across all gestational ages compared to females. At term, both ventricles had higher TRPM7 expression at 6 h old than at birth. In preterm piglets, TRPM7 expression only increased postnatally in the right ventricle following maternal glucocorticoid exposure. At 12-24 h old, TRPM7 expression in both ventricles was lower than levels in 6 h old term Caesar piglets (113 days). Male preterm piglets may have immature myocardial Ca2+ handling and this could contribute to their poorer outcomes. Increased TRPM7 expression is the mature response to birth that is missing in preterm neonates. TRPM7 could serve as a novel target to improve cardiac function in preterm neonates.

Plasma Leak From the Circulation Contributes to Poor Outcomes for Preterm Infants: A Working Hypothesis.

Preterm infants are at high risk of death and disability resulting from brain injury. Impaired cardiovascular function leading to poor cerebral oxygenation is a significant contributor to these adverse outcomes, but current therapeutic approaches have failed to improve outcome. We have re-examined existing evidence regarding hypovolemia and have concluded that in the preterm infant loss of plasma from the circulation results in hypovolemia; and that this is a significant driver of cardiovascular instability and thus poor cerebral oxygenation. High capillary permeability, altered hydrostatic and oncotic pressure gradients, and reduced lymphatic return all combine to increase net loss of plasma from the circulation at the capillary. Evidence is presented that early hypovolemia occurs in preterm infants, and that capillary permeability and pressure gradients all change in a way that promotes rapid plasma loss at the capillary. Impaired lymph flow, inflammation and some current treatment strategies may further exacerbate this plasma loss. A framework for testing this hypothesis is presented. Understanding these mechanisms opens the way to novel treatment strategies to support cardiovascular function and cerebral oxygenation, to replace current therapies, which have been shown not to change outcomes.

Capillary Triglycerides in Late Pregnancy-Challenging to Measure, Hard to Interpret: A Cohort Study of Practicality.

BACKGROUND: Maternal triglycerides are increasingly recognised as important predictors of infant growth and fat mass. The variability of triglyceride patterns during the day and their relationship to dietary intake in women in late pregnancy have not been explored. This prospective cohort study aimed to examine the utility of monitoring capillary triglycerides in women in late pregnancy. METHODS: Twenty-nine women (22 with gestational diabetes (GDM) and 7 without) measured capillary glucose and triglycerides using standard meters at home for four days. On two of those days, they consumed one of two standard isocaloric breakfast meals: a high-fat/low-carbohydrate meal (66% fat) or low fat/high carbohydrate meal (10% fat). Following the standard meals, glucose and triglyceride levels were monitored. RESULTS: Median capillary triglycerides were highly variable between women but did not differ between GDM and normoglycaemic women. There was variability in capillary triglycerides over four days of home monitoring and a difference in incremental area under the curve for capillary triglycerides and glucose between the two standard meals. The high-fat standard meal lowered the incremental area under the curve for capillary glucose (p < 0.0001). Fasting (rho 0.66, p = 0.0002) and postpradial capillary triglycerides measured at home correlated with venous triglyceride levels. CONCLUSIONS: The lack of differences in response to dietary fat intake and the correlation between capillary and venous triglycerides suggest that monitoring of capillary triglycerides before and after meals in pregnancy is unlikely to be useful in the routine clinical practice management of women with gestational diabetes mellitus.

Body composition in very preterm infants before discharge is associated with macronutrient intake.

Very preterm infants experience poor postnatal growth relative to intra-uterine growth rates but have increased percentage body fat (%fat). The aim of the present study was to identify nutritional and other clinical predictors of infant %fat, fat mass (FM) (g) and lean mass (LM) (g) in very preterm infants during their hospital stay. Daily intakes of protein, carbohydrate, lipids and energy were recorded from birth to 34 weeks postmenstrual age (PMA) in fifty infants born <32 weeks. Clinical illness variables and anthropometric data were also collected. Body composition was assessed at 34-37 weeks PMA using the PEA POD Infant Body Composition System. Multiple regression analysis was used to identify independent predictors of body composition (%fat, FM or LM). Birth weight, birth weight z-score and PMA were strong positive predictors of infant LM. After adjustment for these factors, the strongest nutrient predictors of LM were protein:carbohydrate ratios (102-318 g LM/0·1 increase in ratio, P = 0·006-0·015). Postnatal age (PNA) and PMA were the strongest predictors of infant FM or %fat. When PNA and PMA were accounted for a higher intake of energy (-1·41 to -1·61 g FM/kJ per kg per d, P = 0·001-0·012), protein (-75·5 to -81·0 g FM/g per kg per d, P = 0·019-0·038) and carbohydrate (-27·2 to -30·0 g FM/g per kg per d, P = 0·012-0·019) were associated with a lower FM at 34-37 weeks PMA. Higher intakes of energy, protein and carbohydrate may reduce fat accumulation in very preterm infants until at least 34-37 weeks PMA.

Probiotics for the Prevention of Gestational Diabetes Mellitus in Overweight and Obese Women: Findings From the SPRING Double-Blind Randomized Controlled Trial.

OBJECTIVE: Given the role of gut microbiota in regulating metabolism, probiotics administered during pregnancy might prevent gestational diabetes mellitus (GDM). This question has not previously been studied in high-risk overweight and obese pregnant women. We aimed to determine whether probiotics (Lactobacillus rhamnosus and Bifidobacterium animalis subspecies lactis) administered from the second trimester in overweight and obese women prevent GDM as assessed by an oral glucose tolerance test (OGTT) at 28 weeks' gestation. Secondary outcomes included maternal and neonatal complications, maternal blood pressure and BMI, and infant body composition. RESEARCH DESIGN AND METHODS: This was a double-blind randomized controlled trial of probiotic versus placebo in overweight and obese pregnant women in Brisbane, Australia. RESULTS: The study was completed in 411 women. GDM occurred in 12.3% (25 of 204) in the placebo arm and 18.4% (38 of 207) in the probiotics arm (P = 0.10). At OGTT, mean fasting glucose was higher in women randomized to probiotics (79.3 mg/dL) compared with placebo (77.5 mg/dL) (P = 0.049). One- and two-hour glucose measures were similar. Preeclampsia occurred in 9.2% of women randomized to probiotics compared with 4.9% in the placebo arm (P = 0.09). Excessive weight gain occurred in 32.5% of women in the probiotics arm (55 of 169) compared with 46% in the placebo arm (81 of 176) (P = 0.01). Rates of small for gestational age (<10th percentile) were 2.4% in the probiotics arm (5 of 205) and 6.5% in the placebo arm (13 of 199) (P = 0.042). There were no differences in other secondary outcomes. CONCLUSIONS: The probiotics used in this study did not prevent GDM in overweight and obese pregnant women.

Effect of Delayed Cord Clamping on Cerebral Oxygenation in Very Preterm Infants.

BACKGROUND AND OBJECTIVE: The mechanism of reported benefits of delayed cord clamping (DCC) are unclear. We aimed to determine whether DCC compared to immediate cord clamping (ICC) in very preterm infants improves cerebral oxygenation in the first 24 h. STUDY DESIGN: This is a prospective study of a subset of infants at < 30 weeks of gestation who were randomised to DCC (≥60 s) or ICC (< 10 s) and required an indwelling arterial catheter. Regional cerebral oxygenation (rScO2), blood pressure, PI, and peripheral saturation were measured and cerebral fractional tissue oxygen extraction (cFTOE) calculated for the following 3 time intervals: 3-6, 6-12, and 12-28 h of age. Functional ultrasound measures including superior vena cava flow, right ventricular output, ductus arteriosus size and shunt and anterior cerebral artery resistive index were determined. RESULTS: The mean (±SD) gestation and birth weight of the 51 study infants were 27 ± 1 weeks and 1,046 ± 241 g respectively. Twenty infants received DCC and 31 received ICC. Baseline demographics were similar between the 2 groups. Comparing DCC and ICC infants, there was no difference in rScO2 or cFTOE at any time point. Three out of 20 infants did not receive DCC due to clinical concerns. A sensitivity analysis revealed that cord clamping ≥30 s was significantly associated with increased rScO2 and decreased cFTOE at all 3 time points after adjusting for gestation. CONCLUSION: Although DCC was not associated with changes in cerebral oxygenation overall, sensitivity analysis suggested a possible effect of an increased rScO2 and a decreased cFTOE with ≥30 s of DCC.

Supporting preterm cardiovascular function.

Preterm infants are at higher risk of adverse neurodevelopmental outcomes. Inadequate cerebral oxygen delivery resulting from poor cardiovascular function is likely to be a significant contributor to preterm brain injury. In this context, improved support of cardiovascular function is integral to improving preterm outcomes. Many of the treatments used to support preterm cardiovascular function are based on adult physiology and may not be appropriate for the unique physiology of the preterm infant. The preterm heart is structurally immature with reduced contractility and low cardiac output. However, there is limited evidence that inotropic support with dopamine and/or dobutamine is effective in preterm babies. Hypovolemia may also contribute to poor preterm cardiovascular function; there is evidence that capillary leakage results in considerable loss of plasma from the circulation of newborn preterm babies. In addition, the vasoconstrictor response to acute stimuli does not develop until quite late in gestation and is limited in the preterm infant. This may lead to inappropriate vasodilatation adding to functional hypovolemia. The first line treatment for hypotension in preterm infants is volume expansion with crystalloid solutions, but this has limited efficacy in the preterm infant. More effective methods of volume expansion are required. Effective support of preterm cardiovascular function requires better understanding of preterm cardiovascular physiology so that treatments can target mechanisms that are sufficiently mature to respond.

Reduced blood volume decreases cerebral blood flow in preterm piglets.

KEY POINTS: Preterm infants often have poor cardiovascular function that is associated with adverse neurodevelopmental outcomes. Preterm infants may be vulnerable to hypovolaemia due to excessive vasodilatation and leaky capillaries. Following reduction in blood volume, cardiac output and mean arterial pressure were reduced to the same extent in term and preterm piglets. Cerebral blood flow was maintained following blood volume reduction in term but not in preterm piglets. Effective detection and treatment of functional hypovolaemia may reduce the risk of brain injury in preterm infants. ABSTRACT: Preterm infants often have impaired cardiovascular function that may contribute to poor neurodevelopmental outcomes. The study aimed to determine the effects of reduced blood volume on cardiovascular function, including cerebral blood flow, in preterm and term piglets. In preterm (97/115 days) and term piglets, up to 10% of the estimated blood volume was removed. Removal of blood was stopped if MAP dropped below 20 mmHg. Heart rate, cardiac contractility and relaxation, cardiac output, mean arterial pressure (MAP), and cerebral blood flow were measured at baseline and again after blood volume reduction. The volume of blood removed was less in preterm piglets than in term piglets (5.1 ± 1.8 vs. 7.7 ± 0.9 mL kg-1 , mean ± SD, P < 0.001). Cardiac output and MAP decreased to the same extent in term and preterm piglets. Cerebral blood flow decreased in preterm but not term piglets and cerebral vascular conductance increased in term piglets only. Compensatory responses to maintain cerebral blood flow after blood volume reduction are active in term piglets but not in preterm piglets. As a result, even a small reduction in blood volume, or an increase in the capacity of the circulatory system leading to functional hypovolaemia, may lead to a significant reduction in cerebral blood flow and contribute to brain injury in preterm neonates.

Structure, organization and tissue expression of the pig SLC13A1 and SLC13A4 sulfate transporter genes.

Sulfate is an obligate nutrient for fetal growth and development. In mice, the renal Slc13a1 sulfate transporter maintains high maternal circulating levels of sulfate in pregnancy, and the placental Slc13a4 sulfate transporter mediates sulfate supply to the fetus. Both of these genes have been linked to severe embryonal defects and fetal loss in mice. However, the clinical significance of SLC13A1 and SLC13A4 in human gestation is unknown. One approach towards understanding the potential involvement of these genes in human fetal pathologies is to use an animal model, such as the pig, which mimics the developmental trajectory of the human fetus more closely than the previously studied mouse models. In this study, we determined the tissue distribution of pig SLC13A1 and SLC13A4 mRNA, and compared the gene, cDNA and protein sequences of the pig, human and mouse homologues. Pig SLC13A1 mRNA was expressed in the ileum and kidney, whereas pig SLC13A4 mRNA was expressed in the placenta, choroid plexus and eye, which is similar to the tissue distribution in human and mouse. The pig SLC13A1 gene contains 15 exons spread over 76 kb on chromosome 8, and encodes a protein of 594 amino acids that shares 90% and 85% identity with the human and mouse homologues, respectively. The pig SLC13A4 gene is located approximately 11 Mb from SLC13A1 on chromosome 8, and contains 16 exons spanning approximately 70 kb. The pig SLC13A4 protein contains 626 amino acids that share 91% and 90% identity with human and mouse homologues, respectively. The 5'-flanking region of SLC13A1 contains several putative transcription factor binding sites, including GATA-1, GATA-3, Oct1 and TATA-box consensus sequences, which are conserved in the homologous human and mouse sequences. The 5'-flanking sequence of SLC13A4 contains multiple putative transcription factor consensus sites, including GATA-1, TATA-box and Vitamin D responsive elements. This is the first report to define the tissue distribution of pig SLC13A1 and SLC13A4 mRNAs, and compare the gene, cDNA, 5'-flanking region and protein sequences to human and mouse.

Review: Is rapid fat accumulation in early life associated with adverse later health outcomes?

This review discusses ways in which the maternal environment and placental function affect the birth weight and adult health outcomes of offspring. These maternal and placental factors have varying and sometimes opposing effects on birth weight, resulting in infants that are born small for gestational age (SGA), large for gestational age (LGA) or preterm. However, all these alterations in weight have similar effects on adult health, increasing the risk of obesity and its associated cardiovascular and metabolic disorders. While birth weight has been used as a marker for risk of adverse adult health, we propose that a common feature of all these scenarios - early accumulation of excess body fat - may be a better marker than birth weight alone. Furthermore, altered neonatal fat accumulation may be more closely related to the mechanism by which maternal environment and placental adaptation mediate effects on adult health. We suggest that more research should be focussed on early fat accretion, factors that promote fat accretion and if it can be avoided, and whether it would be beneficial to try to reduce fat accumulation in early life.

Inotropes do not increase cardiac output or cerebral blood flow in preterm piglets.

BACKGROUND: The preterm newborn is at high risk of developing cardiovascular compromise during the first day of life and this is associated with increased risk of brain injury. Standard treatments are volume expansion and administration of inotropes, typically dopamine and/or dobutamine, but there is limited evidence that inotropes improve clinical outcomes. This study investigated the efficacy of dopamine and dobutamine for the treatment of cardiovascular compromise in the preterm newborn using a piglet model. METHODS: Preterm and term piglets were assigned to either dopamine, dobutamine or control infusions. Heart rate, left ventricular contractility, cardiac output, blood pressure, and cerebral and regional blood flows were measured during baseline, low (10 µg/kg/h), and high (20 µg/kg/h) dose infusions. RESULTS: At baseline, preterm piglets had lower cardiac contractility, cardiac output, blood pressure, and cerebral blood flow compared to term piglets. The response of preterm piglets to either dopamine or dobutamine administration was less than in term piglets. In both preterm and term piglets, cardiac output and cerebral blood flow were unaltered by either inotrope. CONCLUSION: In order to provide better cardiovascular support, it may be necessary to develop treatments that target receptors with a more mature profile than adrenoceptors in the preterm newborn.

Estimation of fat-free mass in Asian neonates using bioelectrical impedance analysis.

The aims of this study were to develop and validate a prediction equation of fat-free mass (FFM) based on bioelectrical impedance analysis (BIA) and anthropometry using air-displacement plethysmography (ADP) as a reference in Asian neonates and to test the applicability of the prediction equations in an independent Western cohort. A total of 173 neonates at birth and 140 at two weeks of age were included. Multiple linear regression analysis was performed to develop the prediction equations in a two-third randomly selected subset and validated on the remaining one-third subset at each time point and in an independent Queensland cohort. FFM measured by ADP was the dependent variable, and anthropometric measures, sex and impedance quotient (L2/R50) were independent variables in the model. Accuracy of prediction equations was assessed using intra-class correlation and Bland-Altman analyses. L2/R50 was the significant predictor of FFM at week two but not at birth. Compared with the model using weight, sex and length, including L2/R50 slightly improved the prediction with a bias of 0·01 kg with 2 sd limits of agreement (LOA) (0·18, -0·20). Prediction explained 88·9 % of variation but not beyond that of anthropometry. Applying these equations to the Queensland cohort provided similar performance at the appropriate age. However, when the Queensland equations were applied to our cohort, the bias increased slightly but with similar LOA. BIA appears to have limited use in predicting FFM in the first few weeks of life compared with simple anthropometry in Asian populations. There is a need for population- and age-appropriate FFM prediction equations.

PPREMO: a prospective cohort study of preterm infant brain structure and function to predict neurodevelopmental outcome.

BACKGROUND: More than 50 percent of all infants born very preterm will experience significant motor and cognitive impairment. Provision of early intervention is dependent upon accurate, early identification of infants at risk of adverse outcomes. Magnetic resonance imaging at term equivalent age combined with General Movements assessment at 12 weeks corrected age is currently the most accurate method for early prediction of cerebral palsy at 12 months corrected age. To date no studies have compared the use of earlier magnetic resonance imaging combined with neuromotor and neurobehavioural assessments (at 30 weeks postmenstrual age) to predict later motor and neurodevelopmental outcomes including cerebral palsy (at 12-24 months corrected age). This study aims to investigate i) the relationship between earlier brain imaging and neuromotor/neurobehavioural assessments at 30 and 40 weeks postmenstrual age, and ii) their ability to predict motor and neurodevelopmental outcomes at 3 and 12 months corrected age. METHODS/DESIGN: This prospective cohort study will recruit 80 preterm infants born ≤ 30 week's gestation and a reference group of 20 healthy term born infants from the Royal Brisbane & Women's Hospital in Brisbane, Australia. Infants will undergo brain magnetic resonance imaging at approximately 30 and 40 weeks postmenstrual age to develop our understanding of very early brain structure at 30 weeks and maturation that occurs between 30 and 40 weeks postmenstrual age. A combination of neurological (Hammersmith Neonatal Neurologic Examination), neuromotor (General Movements, Test of Infant Motor Performance), neurobehavioural (NICU Network Neurobehavioural Scale, Premie-Neuro) and visual assessments will be performed at 30 and 40 weeks postmenstrual age to improve our understanding of the relationship between brain structure and function. These data will be compared to motor assessments at 12 weeks corrected age and motor and neurodevelopmental outcomes at 12 months corrected age (neurological assessment by paediatrician, Bayley scales of Infant and Toddler Development, Alberta Infant Motor Scale, Neurosensory Motor Developmental Assessment) to differentiate atypical development (including cerebral palsy and/or motor delay). DISCUSSION: Earlier identification of those very preterm infants at risk of adverse neurodevelopmental and motor outcomes provides an additional period for intervention to optimise outcomes. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry ACTRN12613000280707. Registered 8 March 2013.

Expression of genes of the cardiac and renal renin-angiotensin systems in preterm piglets: is this system a suitable target for therapeutic intervention?

OBJECTIVES: The newborn circulating, cardiac and renal renin-angiotensin systems (RASs) are essential for blood pressure control, and for cardiac and renal development. If cardiac and renal RASs are immature this may contribute to cardiovascular compromise in preterm infants. This study measured mRNA expression of cardiac and renal RAS components in preterm, glucocorticoid (GC) exposed preterm, and term piglets. METHODS: Renal and cardiac RAS mRNA levels were measured using real-time polymerase chain reaction (PCR). Genes studied were: (pro)renin receptor, renin, angiotensinogen, angiotensin converting enzyme (ACE), ACE2, angiotensin type 1 receptor (AT1R) and angiotensin type 2 receptor (AT2R). RESULTS: All the genes studied were expressed in the kidney; neither renin nor AT2R mRNA were detected in the heart. There were no gestational changes in (pro)renin receptor, renin, ACE or AT1R mRNA levels. Right ventricular angiotensinogen mRNA levels in females were lower in preterm animals than at term, and GC exposure increased levels in male piglets. Renal angiotensinogen mRNA levels in female term piglets were lower than females from both preterm groups, and lower than male term piglets. Left ventricular ACE2 mRNA expression was lower in GC treated preterm piglets. Renal AT2R mRNA abundance was highest in GC treated preterm piglets, and the AT1R/AT2R ratio was increased at term. CONCLUSIONS: Preterm cardiac and renal RAS mRNA levels were similar to term piglets, suggesting that immaturity of these RASs does not contribute to preterm cardiovascular compromise. Since preterm expression of both renal and cardiac angiotensin II-AT1R is similar to term animals, cardiovascular dysfunction in the sick preterm human neonate might be effectively treated by agents acting on their RASs.

Endogenous angiotensins and catecholamines do not reduce skin blood flow or prevent hypotension in preterm piglets.

Endocrine control of cardiovascular function is probably immature in the preterm infant; thus, it may contribute to the relative ineffectiveness of current adrenergic treatments for preterm cardiovascular compromise. This study aimed to determine the cardiovascular and hormonal responses to stress in the preterm piglet. Piglets were delivered by cesarean section either preterm (97 of 115 days) or at term (113 days). An additional group of preterm piglets received maternal glucocorticoids as used clinically. Piglets were sedated and underwent hypoxia (4% FiO2 for 20 min) to stimulate a cardiovascular response. Arterial blood pressure, skin blood flow, heart rate and plasma levels of epinephrine, norepinephrine, angiotensin II (Ang II), angiotensin-(1-7) (Ang-(1-7)), and cortisol were measured. Term piglets responded to hypoxia with vasoconstriction; preterm piglets had a lesser response. Preterm piglets had lower blood pressures throughout, with a delayed blood pressure response to the hypoxic stress compared with term piglets. This immature response occurred despite similar high levels of circulating catecholamines, and higher levels of Ang II compared with term animals. Prenatal exposure to glucocorticoids increased the ratio of Ang-(1-7):Ang II. Preterm piglets, in contrast to term piglets, had no increase in cortisol levels in response to hypoxia. Preterm piglets have immature physiological responses to a hypoxic stress but no deficit of circulating catecholamines. Reduced vasoconstriction in preterm piglets could result from vasodilator actions of Ang II. In glucocorticoid exposed preterm piglets, further inhibition of vasoconstriction may occur because of an increased conversion of Ang II to Ang-(1-7).

Exposure to intrauterine inflammation leads to impaired function and altered structure in the preterm heart of fetal sheep.

Intrauterine inflammation is a major contributor to preterm birth and has adverse effects on preterm neonatal cardiovascular physiology. Cardiomyocyte maturation occurs in late gestation in species such as humans and sheep. We tested the hypothesis that intrauterine inflammation has deleterious effects on cardiac function in preterm sheep which might be explained by altered cardiomyocyte proliferation and maturation. Pregnant ewes received an ultrasound-guided intra-amniotic injection of lipopolysaccharide (LPS) or saline 7 days prior to delivery at day 127 of pregnancy (term 147 days). Cardiac contractility was recorded in spontaneously beating hearts of the offspring, perfused in a Langendorff apparatus. Saline-filled latex balloons were inserted into the left ventricle (LV) and right ventricle (RV). Responsiveness to isoprenaline and stop-flow/reperfusion was assessed. In other experiments, hearts were perfusion-fixed, and cardiomyocyte nuclearity, volume and number were determined. ß-Adrenoceptor mRNA levels were determined in unfixed tissue. In hearts of LPS-exposed fetuses, contractility in the LV and RV was suppressed by ~40% and cardiomyocyte numbers were reduced by ~25%. Immature mono-nucleated cardiomyocytes had lower volumes (~18%), whereas mature bi-nucleated cardiomyocyte volume was ~77% greater. Although basal coronary flow was significantly increased by 21±7% in LPS-exposed hearts, following ischaemia/reperfusion (IR), end-diastolic pressure was increased 2.4±0.3-fold and infarct area was increased 3.2±0.6-fold compared with those in controls. Maximum responsiveness to isoprenaline was enhanced by LPS, without an increase in ß-adrenoceptor mRNA, suggesting altered second messenger signalling. Intrauterine inflammation altered cardiac growth, suppressed contractile function and enhanced responsiveness to stress. Although these effects may ensure immediate survival, they probably contribute to the increased vulnerability of organ perfusion in preterm neonates.

Expression of adrenoceptor subtypes in preterm piglet heart is different to term heart.

Preterm delivery increases the risk of inadequate systemic blood flow and hypotension, and many preterm infants fail to respond to conventional inotrope treatments. If the profile of cardiac adrenoceptor subtypes in the preterm neonate is different to that at term this may contribute to these clinical problems. This study measured mRNA expression of ß1, ß2, α1A, α2A and α2B-adrenoceptor subtypes by real time PCR in term (113d), preterm (91d) and preterm piglets (91d) exposed to maternal glucocorticoid treatment. Abundance of ß-adrenoceptor binding sites in the left ventricle was measured using saturation binding assays. Relative abundance of ß1-adrenoceptor mRNA in untreated preterm hearts was ∼50% of term abundance in both left and right ventricles (P<0.001). Trends in receptor binding site density measurements supported this observation (P = 0.07). Glucocorticoid exposure increased ß1-adrenoceptor mRNA levels in the right ventricle of preterm hearts (P = 0.008) but did not alter expression in the left ventricle (P>0.1). Relative abundance of α1A-adrenoceptor mRNA was the same in preterm and term piglet hearts (P = >0.1) but was reduced by maternal glucocorticoid treatment (P<0.01); α2A-adrenoceptor mRNA abundance was higher in untreated and glucocorticoid exposed preterm piglet hearts than in term piglets (P<0.001). There was no difference between male and female piglets in mRNA abundance of any of the genes studied. In conclusion, there is reduced mRNA abundance of ß1-adrenoceptors in the preterm pig heart. If this lower expression of ß-adrenoceptors occurs in human preterm infants, it could explain their poor cardiovascular function and their frequent failure to respond to commonly used inotropes.

Effects of glucocorticoid exposure on growth and structural maturation of the heart of the preterm piglet.

Inadequate maintenance of systemic blood flow in neonates following preterm birth is associated with increased morbidity and mortality, and may be due in part to structural immaturity of the myocardium. Maternal glucocorticoid administration is associated with improved cardiovascular function, and possibly promotes structural maturation of the myocardium. This study assessed the structural maturity of the myocardium in male and female preterm and term piglets, and preterm piglets exposed to a regimen of maternal glucocorticoids as used clinically. In preterm, term and glucocorticoid exposed preterm piglets cardiomyocyte maturity was examined by measuring the proportion of binucleated myocytes and the volumes of single living ventricular cardiomyocytes with fluorescence microscopy. Ventricular apoptosis and proliferation were measured by immunohistochemistry. Preterm piglet hearts had fewer binucleated myocytes, smaller myocytes, and more proliferative and fewer apoptotic nuclei than term hearts. Maternal glucocorticoid treatment resulted in increased binucleation with no increase in myocyte volume, and levels of proliferation and apoptosis that were more similar to the term heart. Atrial weights were increased and in female piglets there was an increase in the ratio of left to right ventricular weight. The observed changes in atrial mass and myocyte structural maturation correlated with changes in cardiac function of isolated hearts of littermates. In conclusion, the association between increased myocardial maturation following glucocorticoid exposure, improved cardiac function in littermates, and clinical improvement in human neonatal cardiac function exposed to antenatal glucocorticoids, suggests that glucocorticoid exposure contributes to improved cardiovascular function in preterm infants by promoting myocardial structural maturity.