Is baroreflex control of sympathetic activity and heart rate active in the preterm fetal sheep?

Booth, Lindsea C.; Malpas, Simon C.; Barrett, Carolyn J.; Guild, Sarah-Jane; Gunn, Alistair J.

doi:10.1152/ajpregu.90624.2008

Cited by 22 publications

(33 citation statements)

References 55 publications

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“…Because we did not catheterize control fetuses, hemodynamic data are not available for comparison. However, other investigators have reported fetal baseline blood pressure of 37-38 mmHg and heart rates of 182-191 beats per minute (bpm) at a similar gestational age (2,41). Coadministration of NTP with ANG II was also accompanied by an increase in blood pressure, although significantly less than with ANG II alone (Fig.…”

Section: Resultsmentioning

confidence: 87%

ANG II modulation of cardiac growth and remodeling in immature fetal sheep

Sandgren

Scholz

Segar

2015

American Journal of Physiology-Regulatory, Integrative and Comp

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Sandgren J, Scholz TD, Segar JL. ANG II modulation of cardiac growth and remodeling in immature fetal sheep. Am J Physiol Regul Integr Comp Physiol 308: R965-R972, 2015. First published March 25, 2015 doi:10.1152/ajpregu.00034.2015.-ANG II increases fetal blood pressure and stimulates fetal heart growth; however, little is known regarding its direct effects on cardiomyocytes in vivo. We sought to determine whether ANG II stimulates heart growth and cardiomyocyte hypertrophy and/or hyperplasia in utero in the immature fetal heart independent of the effects on cardiac afterload. In twin gestation, fetal sheep at ϳ100 days gestation (term 145 days), one fetus received a chronic (6 days) infusion of ANG II alone (50 g·kg Ϫ1 ·min Ϫ1 ) or ANG II plus nitroprusside (NTP) to attenuate the increase in blood pressure; noninstrumented twins served as controls. ANG II alone, but not ANG II ϩ NTP resulted in a significant increase in heart mass (left and right ventricle ϩ septum, corrected for body weight) compared with controls. ANG II, but not ANG IIϩNTP, also significantly increased cardiomyocyte area compared with control and increased the percentage of binucleated myocytes. ANG II with or without concomitant infusion of NTP increased cardiac PCNA expression, a marker of proliferation. Steady-state protein expression of terminal mitogen-activated protein kinases, cyclin B1, cyclin E1, and p21 were similar among groups. We conclude that in vivo, ANG II increases fetal cardiac mass via cardiomyocyte hypertrophy, differentiation, and to a lesser extent hyperplasia. The effects of ANG II on hypertrophy appear dependent upon the increase in blood pressure (mechanical load), whereas effects on proliferation are load-independent.heart; cardiomyocyte; hypertrophy; hyperplasia STUDIES OF THE FETAL SHEEP heart, long used as a model of human cardiac development, demonstrate marked changes of the myocardium during the last one-third of gestation. In addition to developmental changes in vascularity and myocyte myofibrillar and mitochondrial content, there is a marked increase in the number of cardiomyocytes within the heart, as well as a transition from mononucleated to binucleated (terminally differentiated) myocytes (19,38). In the sheep heart, the transition from mononucleated to binucleated cells begins around 100 days of gestation (term ϳ145 days), such that, at term, ϳ70% of cardiomyocytes are binucleated, or terminally differentiated (19). Both humoral and hemodynamic forces influence cardiac growth and cardiomyocyte proliferation and maturation, although mechanisms governing the normal heart growth process are not well understood (6, 10, 16 -18, 26, 37). Regulation of this developmental process is essential, given that cardiomyocyte endowment is essentially determined by birth and that postnatal proliferative capacity is limited. Disruption of this process, with resultant underendowment of the heart with myocytes, as may occur with fetal hypoxia or undernutrition, may increase susceptibility to cardiac failure later in life...

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Section: Resultsmentioning

confidence: 87%

ANG II modulation of cardiac growth and remodeling in immature fetal sheep

Sandgren

Scholz

Segar

2015

American Journal of Physiology-Regulatory, Integrative and Comp

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“…First, the different pathways of the baroreflex feedback system mature at different rates. In preterm sheep of 0.7 GA, there is probably no significant control by the renal sympathetic nerve, which regulates vascular resistance (18,33), whereas in term sheep, vascular resistance control is present (31). In our study, fetal sheep were instrumented at 0.7 GA and maturational changes were studied between 0.75 and 0.80 GA.…”

Section: Maturational Effects Of Baroreflex Activitymentioning

confidence: 87%

“…The gradual decrease of baroreflex sensitivity and increase in delay between variations in heart rate and SBP suggest that hypoxia-ischemia results in a deregulation of the baroreceptor reflex arc. A decreased LF transfer gain and increased delay may result from changes in the dynamics of the sympathetic and parasympathetic pathways and/or from changes in the balance between these pathways (6,17,18,23). Because the parasympathetic effect on heart rate changes is fast as compared with the sympathetic effect, increased delay may indicate a greater relative contribution of sympathetic regulation.…”

Section: Long-term Effects Of Hypoxia-ischemiamentioning

confidence: 99%

“…There is, however, conflicting evidence on the fetal and postnatal development of baroreceptor reflex function. Although some studies show increasing baroreflex sensitivity with age, other studies show no significant maturational change (15)(16)(17)(18). The cardiovascular system responds to hypoxia-ischemia by changing heart rate and redistributing cardiac output to preserve the limited energy resources and maintain adequate supply to the brain.…”

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confidence: 99%

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Heart rate–mediated blood pressure control in preterm fetal sheep under normal and hypoxic–ischemic conditions

et al. 2013

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Background:The understanding of hypoxemia-induced changes in baroreflex function is limited and may be studied in a fetal sheep experiment before, during, and after standardized hypoxic conditions. Methods: Preterm fetal lambs were instrumented at 102 d gestation (term: 146 d). At 106 d, intrauterine hypoxia-ischemia was induced by 25 min of umbilical cord occlusion (UCO). Baroreflex-related fluctuations were calculated at 30-min intervals during the first week after UCO by transfer function (crossspectral) analysis between systolic blood pressure (SBP) and R-R interval fluctuations, estimated in the low-frequency (LF, 0.04-0.15 Hz) band. LF transfer gain (baroreflex sensitivity) and delay (s) reflect the baroreflex function. results: Baseline did not differ in LF transfer gain and delay between controls and the UCO group. In controls, LF gain showed postnatal increase. By contrast, LF gain gradually decreased in the UCO group, resulting in significantly lower values 4-7 d after UCO. In the UCO group, LF delay increased and differed significantly from controls. conclusion: Our results show that intrauterine hypoxiaischemia results in reduced baroreflex sensitivity over a period of 7 d, indicating limited efficacy to buffer BP changes by adapting heart rate. Cardiovascular dysregulation may augment already present cerebral damage after systemic hypoxiaischemia in the reperfusion period.P reterm infants have a higher incidence of neurological morbidity and mortality as compared with term infants (1). Neurological sequelae in preterm infants may be the consequence of hypoxia-ischemia during fetal and early postnatal life (2). Hemodynamic factors during hypoxia-ischemia and the posthypoxia-ischemia reperfusion phase contribute considerably to these neurological disorders (3). To ensure adequate blood flow to organs throughout the body, including the brain, blood pressure (BP) is controlled by baroreflex and chemoreflex mechanisms. Under normoxemia, the baroreflex stabilizes perfusion pressure in the face of disturbances of circulatory homeostasis by adapting heart rate, myocardial contraction, and vascular resistance. A poorly developed baroreflex function could contribute to BP instabilities, which may lead to impaired cerebral perfusion or hemorrhage (4). A better understanding of the dynamics underlying the control mechanisms regulating BP may be useful to improve diagnosis of these disorders.Low-frequency (LF) fluctuations in arterial BP with a wavelength of approximately 10 s (also called Mayer waves) have historically been attributed to baroreflex activity (5). The oscillations are assumed to be caused by a feedback control and mediated through the sympathetic and parasympathetic innervations of the baroreflex (6). Assessment of the baroreflex function (i.e., heart rate-mediated BP control) can be performed through quantification of baroreceptor sensitivity. Baroreceptor sensitivity (ms/mm Hg) may simply be defined as the change in heart rate (or R-R interval) in response to changes in arterial BP and may be e...

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“…Premature babies have a high incidence of low blood pressure, especially in the first few days of life, thought to be due to the immaturity of the baroreflex. 47 Further, whereas one third of the total feto-placental blood volume circulates in the placenta of the term neonate, this fraction increases to one half in the preterm infant. 15 The premature neonate is also unprepared for significant metabolic changes at delivery, especially with respect to the production of glucose.…”

Section: Preterm Infantsmentioning

confidence: 99%

Third Stage Practices and the Neonate

Downey

Bewley

2009

Fet. Matern. Med. Rev.

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The third stage of labour is defined as the period following the completed delivery of the newborn until the completed delivery of the placenta and its attached membranes. Whilst to the exhausted labouring woman this stage may be an afterthought, it is a crucial time for fetal-to-neonatal transition. Major changes in anatomy and physiology occur in both mother and baby. It has also been described as ‘potentially the most hazardous part of childbirth, largely due to the risk of postpartum haemorrhage (PPH) on placental separation. Despite this, the current management guidelines are based on an ‘eclectic combination of historical, anecdotal, philosophical and research-based factors.

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Is baroreflex control of sympathetic activity and heart rate active in the preterm fetal sheep?

Abstract: Booth LC, Malpas SC, Barrett CJ, Guild S-J, Gunn AJ, Bennet L. Is baroreflex control of sympathetic activity and heart rate active in the preterm fetal sheep? Am

Cited by 22 publications

References 55 publications

ANG II modulation of cardiac growth and remodeling in immature fetal sheep

ANG II modulation of cardiac growth and remodeling in immature fetal sheep

Heart rate–mediated blood pressure control in preterm fetal sheep under normal and hypoxic–ischemic conditions

Third Stage Practices and the Neonate

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