Véronique Gournay

Perinatal Myocardial DNA and Protein Changes in the Lamb: Effect of Cortisol in the Fetus

Myocardial growth during fetal life is accomplished by proliferation of the number of myocytes (hyperplasia). Shortly after birth, normal growth of the heart is predominantly due to increase in cell size (hypertrophy), and myocytes largely lose the capability to replicate. This change is characterized by a decrease in myocardial DNA concentration and an increase in protein/DNA concentration ratio. Among many of the events associated with birth is an increase in plasma cortisol concentrations in the few days before delivery of the fetus. To determine the possible role of cortisol in the postnatal change in myocardial growth, we measured DNA and protein concentrations in the free walls of the left (LV) and right (RV) ventricles in normal fetal lambs, normal newborn lambs, and in fetal lambs in which cortisone was infused for 72-80 h into the left coronary artery, which we showed does not perfuse the RV free wall. Normally, fetal RV DNA is higher than LV DNA concentration, and DNA/protein ratio is lower in RV than in LV. It is suggested that this could be related to the greater load on the RV. Postnatally, protein concentrations increase progressively, but DNA remains the same in both ventricles, and protein/DNA ratios increase. Cortisol, infused to achieve normal prenatal levels in LV myocardium, markedly decreases LV DNA without affecting RV DNA concentrations. The present study indicates that cortisol inhibits myocyte replication and that cortisol simulates the change in myocardial growth pattern normally occurring after birth. It raises concerns regarding prenatal administration of glucocorticoids to mothers to mature the fetal lungs before preterm delivery.

Development of baroreflex control of heart rate in preterm and full term infants.

Aim: To study baroreflex maturation by measuring, longitudinally, baroreflex sensitivity in preterm (gestational age 24–37 weeks) and full term infants. Methods: Baroreflex sensitivity was quantified once a week, one to seven times, by a totally non-invasive method. Results: Baroreflex sensitivity at birth was lower in the preterm infant and increased with gestational age. It also increased with postnatal age, but the values for the preterm infants at term still tended to be lower than the values for full term babies. Conclusion: Baroreflex control of heart rate is present in the premature infant, but is underdeveloped and increases with postnatal age. Ex utero maturation seems to be delayed compared with in utero maturation assessed by full term values. These results may reflect sympathovagal imbalance in preterm infants and could identify a population more vulnerable to stress.

Assessment of spontaneous baroreflex sensitivity in neonates

AIMS To determine whether it is possible to assess baroreflex sensitivity in neonates by studying only spontaneous variations in systolic blood pressure and heart rate. METHODS ECG and non-invasive blood pressure signals were continuously studied in 14 preterm neonates (term 29-32 weeks) and five term neonates (term 40-41 weeks). Non-invasive blood pressure measures were obtained using a Finapres placed around the child’s wrist. Both signals (ECG and blood pressure), sampled at 400 Hz, were digitised by an A/D converter and stored in a binary mode on magnetic disk. An inhouse software QRS detection algorithm was used to define R peaks of the QRS complexes with an accuracy greater than 2 ms. Four 4 minute periods were recorded in each infant. The slope of the linear regression of RR intervals versus systolic blood pressure was calculated in each period and the mean value of the four slopes was then considered as the index of baroreflex sensitivity (in ms/mm Hg) in each neonate. RESULTS Spontaneous baroreflex sensitivity was lower in preterm neonates than in term neonates (mean(SD): 4.07 (2.19) ms/mm Hg vs 10.23 (2.92) ms/mm Hg). CONCLUSION Baroreflex sensitivity can be assessed in term and preterm neonates by studying spontaneous variations in systolic blood pressure alone. This method could be useful for studying the ontogeny of baroreflex sensitivity and might therefore provide information about the maturation of the autonomic nervous system.

Feasibility of using finger arterial pressure in neonates

The feasibility of using a Finapres device to reproduce the beat to beat signal of arterial blood pressure in eight neonates was assessed and compared with intra-arterial measurement of arterial blood pressure in the umbilical artery, using a catheter. The two methods gave similar results. Continuous recording of arterial blood pressure in neonates using Finapres is feasible and reliable.

Adrenomedullin Increases Pulmonary Blood Flow in Fetal Sheep

We studied the effects of exogenously administered adrenomedullin on fetal pulmonary arterial blood flow in near-term fetal sheep. The hemodynamic effects of a single injection of adrenomedullin into the left pulmonary artery were compared with those of acetylcholine; the effects of repeated injections of adrenomedullin were also studied. In seven unanesthetized fetal sheep, catheters were inserted into the left pulmonary artery to administer drugs, and into the main pulmonary and carotid arteries to measure pressures. An ultrasonic flow transducer was placed around the left pulmonary artery to measure flow continuously. A single 5-μg injection of adrenomedullin (1.90± 0.35 μg/kg of fetal weight) increased pulmonary arterial blood flow significantly, from 17 ± 10 to 120 ± 21 mL/min (p< 0.001). Two micrograms of acetylcholine (0.74 ± 0.14 μg/kg of fetal weight) also increased left pulmonary arterial blood flow, from 18± 16 to 113 ± 37 mL/min, but the effect of adrenomedullin on flow was more prolonged than was that of acetylcholine. Additionally, adrenomedullin and acetylcholine similarly decreased mean pulmonary arterial pressure by 11 and 16%, respectively, but adrenomedullin did not decrease mean carotid arterial pressure to the same degree as acetylcholine (2versus 19%, respectively). Five sequentially repeated injections of adrenomedullin, once every 5 min, increased left pulmonary arterial blood flow significantly in a stepwise manner without significantly changing heart rate or mean pulmonary and carotid arterial pressures. We conclude that exogenously administered adrenomedullin is a pulmonary vasodilator in fetal sheep and has the ability to increase pulmonary blood flow significantly; there is less effect on the systemic circulation. This finding might be important in considering the therapeutic use of this peptide in the management of persistent pulmonary hypertension in the perinatal period.

Mechanisms of adrenomedullin-induced increase of pulmonary blood flow in fetal sheep

Mechanisms of adrenomedullin-induced increases in fetal pulmonary blood flow were examined in 19 near-term fetal sheep using four key blocker drugs: nitric oxide synthase inhibitor (Nω-nitro-L-arginine), calcitonin gene-related peptide (CGRP) receptor blocker, ATP-dependent potassium (KATP) channel blocker (glibenclamide), and cyclooxygenase inhibitor (indomethacin). Catheters were inserted into the left pulmonary artery and superior vena cava to administer drugs and into the main pulmonary and carotid arteries to measure pressures and heart rate. An ultrasonic flow transducer was placed around the left pulmonary artery to measure flow continuously. Adrenomedullin (mean 1.06 µg/kg) was injected into the left pulmonary artery before and after infusion of Nω-nitro-L-arginine (mean 96.5 mg/kg, n = 6), glibenclamide (mean 11.8 mg/kg, n = 6), CGRP receptor blocker (mean 312.0 µg/kg, n = 6), and indomethacin (mean 1.7 mg/kg, n = 8). Blockade was confirmed by appropriate agonist injection. The adrenomedullin-induced response in left pulmonary artery blood flow was inhibited by Nω-nitro-L-arginine (inhibition rate 99%) and significantly attenuated by glibenclamide (inhibition rate 44%); however, no significant changes were found with CGRP receptor blocker or indomethacin (inhibition rate 0 and 17%, respectively). The responses of the main pulmonary and carotid arterial pressures were similarly affected by those blockers. Our data suggest that in the fetal pulmonary circulation, the adrenomedullin-induced increase in pulmonary blood flow depends largely on nitric oxide release and partly on KATP channel activation, and does not involve the CGRP receptor or a cyclooxygenase-mediated mechanism.

Effect of |[beta]|-Adrenergic Stimulation on Oxygen Metabolism in the Fetal Lamb

Catecholamines, which are released into the circulation during stress, increase fetal metabolism. This effect appears to be related to β-adrenoreceptor stimulation. We examined the effect of isoproterenol infusion on umbilical blood flow, oxygen delivery and consumption, and glucose and lactate uptake in late-gestation fetal lambs. Isoproterenol increased umbilical blood flow, but oxygen delivery to the fetus did not increase. Umbilical venous oxygen content fell linearly with the increase in umbilical blood flow. It is proposed that oxygen delivery to the sheep fetus is at or near a maximum and that oxygen delivery cannot be raised by increasing umbilical blood flow because oxygen diffusion at the placental site is limited. Fetal oxygen consumption increased initially but returned to control levels with an increase in infusion rate. Blood glucose concentration increased during isoproterenol infusion; this was due to release of glucose and not because of increased placental uptake. Fetal blood pH values fell in association with elevated lactate levels. It is proposed that elevated glucose concentrations resulted in increased metabolism of glucose, and because oxygen delivery could not be enhanced, increased anaerobic glycolysis caused lactate concentration to rise.

BAROREFLEX SENSITIVITY(BRS) DURING SLEEP STATES IN PRETERM INFANTS 253

State of alertness exerts an influence on autonomic cardiac control (ACC). Heart rate, heart rate variability, and heart rate response to ocular compression have been showed to be different in newborn infants during rapid eye movement (REM) sleep and nonREM sleep. BRS is an another way to assess ACC. The purpose of this study was to measure BRS during routine EEG in 7 preterm infants and compare BRS between REM and non REM sleep. Sleep states were determined on behavior and EEG features. BRS (msec/mmHg) was defined as the slope of linear regression of RR intervals on the electrocardiogram versus systolic blood pressure during spontaneous variations of blood pressure. Postconceptional age, gestational age and postnatal age were 32.8 2.7w, 29.0 2.7w and 2711days, respectively. Results are expressed as mean SD and were analyzed by paired t test. We found that BRS was significantly higher during REM compared to nonREM sleep, 3.60.7vs 2.10.6 msec/mmHg respectively(t=3.9,p<.008). Individual analyzis showed 2 types of response. During REM sleep, BRS increased in 4 infants whereas it did not change in 3(see fig.). Thus, BRS is significantly increased during REM sleep in some infants. Further investigations should be performed to analyse factors which can affect the influence of sleep state on ACC.

DEVELOPMENTAL CHANGES IN BAROREFLEX SENSITIVITY (BRS) IN NEONATES † 243

In fetuses and newborn animals, BRS increases with advancing gestation. The purpose of this study was to assess BRS according to gestationnal age (GA), postnatal age (PNA) ans post conceptional age (PCA) in human newborns, in whom little information is available. We assessed BRS during spontaneous variation in blood pressure measured non invasively with Finapress. BRS (in msec/mmHg) was defined as the slope of the linear regression of RR intervals on the electrocardiogram versus systolic blood pressure. BRS was the mean of the slope measured during 3 different periods, in which the correlation coefficient was higher than.80. Twenty six newborns were enrolled in this study. Eleven very premature (GA 30w [28-32]) and 10 premature (GA 33w [33-34] infants were studied once a week during the first 3 weeks of life. Five term neonates (GA 41w [40-41]) were studied once during the first week of life: thus, 68 BRS value were analyzed. Results are expressed as median[interquartile range] and were statiscally analysed by Kruskall Wallis, Friedman tests and linear regression. Results: The table shows BRS values (msec/mmHg) according to GA and PNA during the three first weeks of life. BRS was mainly correlated to PCA(r=.69, F[1,67]=62, p<.001) and to GA (r=.68, F[1,67]=59, p<.001). BRS was correlated to PNA (r=.48, F[1,32] = 9.2, p<.01) only in the very premature infants (see table). Moreover, BRS assessed after 36 weeks of PCA in three newborns from the very premature group was lower (3.4 [2.2-5.5]) than that of term newborns (p<.02). Conclusion: BRS increases with GA and PCA. Postnatal maturation of BRS is probably slower than intra-utero maturation.

INTRACORONARY INFUSION OF NOREPINEPHRINE SELECTIVELY INCREASES LEFT VENTRICULAR PERFORMANCE IN FETAL LAMBS. † 154

Norepinephrine (NE) infused into the left coronary artery (LCA) of fetal lambs to achieve myocardial concentrations similar to those observed in blood during acute fetal hypoxemia, increases heart rate (HR) and left ventricular output (LVO) without affecting arterial pressure. Infusion into the LCA reaches the LV and septum, but not the RV free wall. We examined the effect of NE infusion into the LCA on LV and RV performance and output in 7 chronically instrumented fetal lambs (gest. age 126-132 d). Aortic (Ao) and pulmonary (PA) ultrasonic flow transducers were implanted to record LVO and RVO. LV and RV contractility were assessed from peak velocity and flow acceleration (dV/dt max). A catheter was inserted into a small branch of the LCA, close to its origin for infusion; NE was infused in amounts of 0.02 μg/min. HR increased from 167 ± 26 to 213 ± 49/min (p < 0.05). LVO rose from 380± 153 to 431 ± 135 ml/min (p < 0.03) and RVO from 498± 170 to 547 ± 250 ml/min (p 0.18). Neither LV nor RV stroke volume (SV) changed significantly. Ao peak flow increased from 1.76 ± 0.24 to 2.01 ± 0.25 L/min (p < 0.001) and Ao dV/dt max rose from 1046 ± 248 to 1496 ± 352 ml/sec/sec (p < 0.005). In contrast PA peak flow (2.04 ± 0.47 to 2.08 ± 0.57) and dV/dt max (2165± 497 to 2207 ± 566) did not change. LV and RV ejection times both fell during NE infusion (LV 139 ± 14 to 116 ± 19 msec, p< 0.02, RV 146 ± 9 to 124 ± 13, p < 0.02), but when adjusted to HR did not change. Thus, even though NE infusion into the LCA selectively enhances LV performance, it does not increase LV SV as compared with the RV. It is concluded that LV and RV ejection in the fetus are largely dependent on loading conditions.