Glucocorticoid Maturation of Fetal Cardiovascular Function

Unravelling the Interplay between Cardiac Metabolism and Heart Regeneration

Ischemic heart disease (IHD) is the leading cause of heart failure (HF) and is a significant cause of morbidity and mortality globally. An ischemic event induces cardiomyocyte death, and the ability for the adult heart to repair itself is challenged by the limited proliferative capacity of resident cardiomyocytes. Intriguingly, changes in metabolic substrate utilisation at birth coincide with the terminal differentiation and reduced proliferation of cardiomyocytes, which argues for a role of cardiac metabolism in heart regeneration. As such, strategies aimed at modulating this metabolism-proliferation axis could, in theory, promote heart regeneration in the setting of IHD. However, the lack of mechanistic understanding of these cellular processes has made it challenging to develop therapeutic modalities that can effectively promote regeneration. Here, we review the role of metabolic substrates and mitochondria in heart regeneration, and discuss potential targets aimed at promoting cardiomyocyte cell cycle re-entry. While advances in cardiovascular therapies have reduced IHD-related deaths, this has resulted in a substantial increase in HF cases. A comprehensive understanding of the interplay between cardiac metabolism and heart regeneration could facilitate the discovery of novel therapeutic targets to repair the damaged heart and reduce risk of HF in patients with IHD.

Molecular mechanisms underlying adverse effects of dexamethasone and betamethasone in the developing cardiovascular system

Antenatal glucocorticoids accelerate fetal lung maturation and reduce mortality in preterm babies but can trigger adverse effects on the cardiovascular system. The mechanisms underlying off-target effects of the synthetic glucocorticoids mostly used, Dexamethasone (Dex) and Betamethasone (Beta), are unknown. We investigated effects of Dex and Beta on cardiovascular structure and function, and underlying molecular mechanism using the chicken embryo, an established model system to isolate effects of therapy on the developing heart and vasculature, independent of effects on the mother or placenta. Fertilized eggs were treated with Dex (0.1 mg kg-1 ), Beta (0.1 mg kg-1 ), or water vehicle (Control) on embryonic day 14 (E14, term = 21 days). At E19, biometry, cardiovascular function, stereological, and molecular analyses were determined. Both glucocorticoids promoted growth restriction, with Beta being more severe. Beta compared with Dex induced greater cardiac diastolic dysfunction and also impaired systolic function. While Dex triggered cardiomyocyte hypertrophy, Beta promoted a decrease in cardiomyocyte number. Molecular changes of Dex on the developing heart included oxidative stress, activation of p38, and cleaved caspase 3. In contrast, impaired GR downregulation, activation of p53, p16, and MKK3 coupled with CDK2 transcriptional repression linked the effects of Beta on cardiomyocyte senescence. Beta but not Dex impaired NO-dependent relaxation of peripheral resistance arteries. Beta diminished contractile responses to potassium and phenylephrine, but Dex enhanced peripheral constrictor reactivity to endothelin-1. We conclude that Dex and Beta have direct differential detrimental effects on the developing cardiovascular system.

Targeting neuro-immune systems to achieve cardiac tissue repair following myocardial infarction: A review of therapeutic approaches from in-vivo preclinical to clinical studies

Myocardial healing following myocardial infarction (MI) toward either functional tissue repair or excessive scarring/heart failure, may depend on a complex interplay between nervous and immune system responses, myocardial ischemia/reperfusion injury factors, as well as genetic and epidemiological factors. Hence, enhancing cardiac repair post MI may require a more patient-specific approach targeting this complex interplay and not just the heart, bearing in mind that the dysregulation or modulation of just one of these systems or some of their mechanisms may determine the outcome either toward functional repair or toward heart failure. In this review we have elected to focus on existing preclinical and clinical in-vivo studies aimed at testing novel therapeutic approaches targeting the nervous and immune systems to trigger myocardial healing toward functional tissue repair. To this end, we have only selected clinical and preclinical in-vivo studies reporting on novel treatments targeting neuro-immune systems to ultimately treat MI. Next, we have grouped and reported treatments under each neuro-immune system. Finally, for each treatment we have assessed and reported the results of each clinical/preclinical study and then discussed their results collectively. This structured approach has been followed for each treatment discussed. To keep this review focused, we have deliberately omitted to cover other important and related research areas such as myocardial ischemia/reperfusion injury, cell and gene therapies as well as any ex-vivo and in-vitro studies. The review indicates that some of the treatments targeting the neuro-immune/inflammatory systems appear to induce beneficial effects remotely on the healing heart post MI, warranting further validation. These remote effects on the heart also indicates the presence of an overarching synergic response occurring across the nervous and immune systems in response to acute MI, which appear to influence cardiac tissue repair in different ways depending on age and timing of treatment delivery following MI. The cumulative evidence arising from this review allows also to make informed considerations on safe as opposed to detrimental treatments, and within the safe treatments to ascertain those associated with conflicting or supporting preclinical data, and those warranting further validation.

Combined Statin and Glucocorticoid Therapy for the Safer Treatment of Preterm Birth

BACKGROUND

Prematurity is strongly associated with poor respiratory function in the neonate. Rescue therapies include treatment with glucocorticoids due to their anti-inflammatory and maturational effects on the developing lung. However, glucocorticoid treatment in the infant can increase the risk of long-term cardiovascular complications including hypertension, cardiac, and endothelial dysfunction. Accumulating evidence implicates a molecular link between glucocorticoid excess and depletion of nitric oxide (NO) bioavailability as a mechanism underlying the detrimental effects of postnatal steroids on the heart and circulation. Therefore, combined glucocorticoid and statin therapy, by increasing NO bioavailability, may protect the developing cardiovascular system while maintaining beneficial effects on the lung.

METHODS

We investigated combined glucocorticoid and statin therapy using an established rodent model of prematurity and combined experiments of cardiovascular function in vivo, with those in isolated organs as well as measurements at the cellular and molecular levels.

RESULTS

We show that neonatal glucocorticoid treatment increases the risk of later cardiovascular dysfunction in the offspring. Underlying mechanisms include decreased circulating NO bioavailability, sympathetic hyper-reactivity, and NO-dependent endothelial dysfunction. Combined neonatal glucocorticoid and statin therapy protects the developing cardiovascular system by normalizing NO and sympathetic signaling, without affecting pulmonary maturational or anti-inflammatory effects of glucocorticoids.

CONCLUSIONS

Therefore, combined glucocorticoid and statin therapy may be safer than glucocorticoids alone for the treatment of preterm birth.

The effect of antenatal corticosteroid use on offspring cardiovascular function: A systematic review

BACKGROUND

Antenatal corticosteroids (ACS) are recommended in threatened preterm labour to improve short-term neonatal outcome. Preclinical animal studies suggest detrimental effects of ACS exposure on offspring cardiac development; their effects in humans are unknown.

OBJECTIVES

To systematically review the human clinical literature to determine the effects of ACS on offspring cardiovascular function.

SEARCH STRATEGY

A systematic review was performed according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines in MEDLINE, EMBASE and Cochrane databases.

SELECTION CRITERIA

Offspring who had been exposed to ACS during fetal life, in comparison with those not receiving steroids, those receiving a placebo or population data, were included. Studies not performed in humans or that did not assess cardiovascular function were excluded.

DATA COLLECTION AND ANALYSIS

Two authors independently screened the studies, extracted the data and assessed the quality of the studies. Results were combined descriptively and analysed using a standardised Excel form.

MAIN RESULTS

Twenty-six studies including 1921 patients were included, most of which were cohort studies of mixed quality. The type of ACS exposure, gestational age at exposure, dose and number of administrations varied widely. Offspring cardiovascular outcomes were assessed from 1 day to 36 years postnatally. The most commonly assessed parameter was arterial blood pressure (18 studies), followed by echocardiography (eight studies), heart rate (five studies), electrocardiogram (ECG, three studies) and cardiac magnetic resonance imaging (MRI, one study). There were no clinically significant effects of ACS exposure on offspring blood pressure. However, there were insufficient studies assessing cardiac structure and function using echocardiography or cardiac MRI to be able to determine an effect.

CONCLUSIONS

The administration of ACS is not associated with long-term effects on blood pressure in exposed human offspring. The effects on cardiac structure and other measures of cardiac function were unclear because of the small number, heterogeneity and mixed quality of the studies. Given the preclinical and human evidence of potential harm following ACS exposure, there is a need for further research to assess central cardiac function in human offspring exposed to ACS.

Heart development and regeneration-a multi-organ effort

Development of the heart, from early morphogenesis to functional maturation, as well as maintenance of its homeostasis are tasks requiring collaborative efforts of cardiac tissue and different extra-cardiac organ systems. The brain, lymphoid organs, and gut are among the interaction partners that can communicate with the heart through a wide array of paracrine signals acting at local or systemic level. Disturbance of cardiac homeostasis following ischemic injury also needs immediate response from these distant organs. Our hearts replace dead muscles with non-contractile fibrotic scars. We have learned from animal models capable of scarless repair that regenerative capability of the heart does not depend only on competency of the myocardium and cardiac-intrinsic factors but also on long-range molecular signals originating in other parts of the body. Here, we provide an overview of inter-organ signals that take part in development and regeneration of the heart. We highlight recent findings and remaining questions. Finally, we discuss the potential of inter-organ modulatory approaches for possible therapeutic use.

Antenatal Glucocorticoid Administration Promotes Cardiac Structure and Energy Metabolism Maturation in Preterm Fetuses

Although the rate of preterm birth has increased in recent decades, a number of preterm infants have escaped death due to improvements in perinatal and neonatal care. Antenatal glucocorticoid (GC) therapy has significantly contributed to progression in lung maturation; however, its potential effects on other organs remain controversial. Furthermore, the effects of antenatal GC therapy on the fetal heart show both pros and cons. Translational research in animal models indicates that constant fetal exposure to antenatal GC administration is sufficient for lung maturation. We have established a premature fetal rat model to investigate immature cardiopulmonary functions in the lungs and heart, including the effects of antenatal GC administration. In this review, we explain the mechanisms of antenatal GC actions on the heart in the fetus compared to those in the neonate. Antenatal GCs may contribute to premature heart maturation by accelerating cardiomyocyte proliferation, angiogenesis, energy production, and sarcoplasmic reticulum function. Additionally, this review specifically focuses on fetal heart growth with antenatal GC administration in experimental animal models. Moreover, knowledge regarding antenatal GC administration in experimental animal models can be coupled with that from developmental biology, with the potential for the generation of functional cells and tissues that could be used for regenerative medical purposes in the future.

Glucocorticoids rapidly promote YAP phosphorylation via the cAMP-PKA pathway to repress mouse cardiomyocyte proliferative potential

Adult mammalian cardiomyocytes (CMs) lose their proliferative potential due to cell-cycle withdrawal and polyploidization and fail to mount a proliferative response to regenerate new CMs after cardiac injury. The decline in the proliferative potential of mammalian CMs occurs in the neonatal period when the endocrine system undergoes drastic changes for adaptation to extra-uterine life. There is an increase in circulating glucocorticoid (GC) levels shortly after birth in mammals, and thus, we sought to determine the roles and mechanisms of GCs in regulating CM proliferation. Here, we showed that GCs suppressed CM proliferation in vitro and in vivo, decreased the total number of CMs, and increased the cross-sectional area of CMs. However, the glucocorticoid receptor antagonist had no effect on CM proliferation. Agonists of adenylate cyclase and protein kinase A (PKA) inhibited CM proliferation, while PKA antagonists or knockdown of PKA alleviated the inhibitory effect of GCs on CM proliferation. GCs and the activation of the cyclic adenosine monophosphate (cAMP)/PKA signaling pathway facilitated yes-associated protein (YAP) phosphorylation in mouse CMs and promoted YAP protein translocation from the nucleus to the cytoplasm. Meanwhile, blocking the cAMP/PKA signaling pathway partially blocked the effect of GCs on YAP protein phosphorylation and YAP protein translocation. Thus, our findings suggest that GCs suppress mouse CM proliferation in vitro and in vivo, through a mechanism that involves targeting the cAMP-PKA-YAP signaling pathway.

Prenatal Hypoxia Affects Foetal Cardiovascular Regulatory Mechanisms in a Sex- and Circadian-Dependent Manner: A Review

Prenatal hypoxia during the prenatal period can interfere with the developmental trajectory and lead to developing hypertension in adulthood. Prenatal hypoxia is often associated with intrauterine growth restriction that interferes with metabolism and can lead to multilevel changes. Therefore, we analysed the effects of prenatal hypoxia predominantly not associated with intrauterine growth restriction using publications up to September 2021. We focused on: (1) The response of cardiovascular regulatory mechanisms, such as the chemoreflex, adenosine, nitric oxide, and angiotensin II on prenatal hypoxia. (2) The role of the placenta in causing and attenuating the effects of hypoxia. (3) Environmental conditions and the mother's health contribution to the development of prenatal hypoxia. (4) The sex-dependent effects of prenatal hypoxia on cardiovascular regulatory mechanisms and the connection between hypoxia-inducible factors and circadian variability. We identified that the possible relationship between the effects of prenatal hypoxia on the cardiovascular regulatory mechanism may vary depending on circadian variability and phase of the days. In summary, even short-term prenatal hypoxia significantly affects cardiovascular regulatory mechanisms and programs hypertension in adulthood, while prenatal programming effects are not only dependent on the critical period, and sensitivity can change within circadian oscillations.

Intrauterine inflammation exacerbates maladaptive remodeling of the immature myocardium after preterm birth in lambs

BACKGROUND

Antenatal conditions that are linked with preterm birth, such as intrauterine inflammation, can influence fetal cardiac development thereby rendering the heart more vulnerable to the effects of prematurity. We aimed to investigate the effect of intrauterine inflammation, consequent to lipopolysaccharide exposure, on postnatal cardiac growth and maturation in preterm lambs.

METHODS

Preterm lambs (~129 days gestational age) exposed antenatally to lipopolysaccharide or saline were managed according to contemporary neonatal care and studied at postnatal day 7. Age-matched fetal controls were studied at ~136 days gestational age. Cardiac tissue was sampled for molecular analyses and assessment of cardiac structure and cardiomyocyte maturation.

RESULTS

Lambs delivered preterm showed distinct ventricular differences in cardiomyocyte growth and maturation trajectories as well as remodeling of the left ventricular myocardium compared to fetal controls. Antenatal exposure to lipopolysaccharide resulted in further collagen deposition in the left ventricle and a greater presence of immune cells in the preterm heart.

CONCLUSIONS

Adverse impacts of preterm birth on cardiac structure and cardiomyocyte growth kinetics within the first week of postnatal life are exacerbated by intrauterine inflammation. The maladaptive remodeling of the cardiac structure and perturbed cardiomyocyte growth likely contribute to the increased vulnerability to cardiac dysfunction following preterm birth.

IMPACT

Preterm birth induces maladaptive cardiac remodeling and adversely impacts cardiomyocyte growth kinetics within the first week of life in sheep. These effects of prematurity on the heart are exacerbated when preterm birth is preceded by exposure to intrauterine inflammation, a common antecedent of preterm birth. Inflammatory injury to the fetal heart coupled with preterm birth consequently alters neonatal cardiac growth and maturation and thus, may potentially influence long-term cardiac function and health.

Breath of Life: Heart Disease Link to Developmental Hypoxia

Heart disease remains one of the greatest killers. In addition to genetics and traditional lifestyle risk factors, we now understand that adverse conditions during pregnancy can also increase susceptibility to cardiovascular disease in the offspring. Therefore, the mechanisms by which this occurs and possible preventative therapies are of significant contemporary interest to the cardiovascular community. A common suboptimal pregnancy condition is a sustained reduction in fetal oxygenation. Chronic fetal hypoxia results from any pregnancy with increased placental vascular resistance, such as in preeclampsia, placental infection, or maternal obesity. Chronic fetal hypoxia may also arise during pregnancy at high altitude or because of maternal respiratory disease. This article reviews the short- and long-term effects of hypoxia on the fetal cardiovascular system, and the importance of chronic fetal hypoxia in triggering a developmental origin of future heart disease in the adult progeny. The work summarizes evidence derived from human studies as well as from rodent, avian, and ovine models. There is a focus on the discovery of the molecular link between prenatal hypoxia, oxidative stress, and increased cardiovascular risk in adult offspring. Discussion of mitochondria-targeted antioxidant therapy offers potential targets for clinical intervention in human pregnancy complicated by chronic fetal hypoxia.

Interdependence of Thyroid and Corticosteroid Signaling in Vertebrate Developmental Transitions

Post-embryonic acute developmental processes mainly allow the transition from one life stage in a specific ecological niche to the next life stage in a different ecological niche. Metamorphosis, an emblematic type of these post-embryonic developmental processes, has occurred repeatedly and independently in various phylogenetic groups throughout metazoan evolution, such as in cnidarian, insects, molluscs, tunicates, or vertebrates. This review will focus on metamorphoses and developmental transitions in vertebrates, including typical larval metamorphosis in anuran amphibians, larval and secondary metamorphoses in teleost fishes, egg hatching in sauropsids and birth in mammals. Two neuroendocrine axes, the hypothalamic-pituitary-thyroid and the hypothalamic-pituitary-adrenal/interrenal axes, are central players in the regulation of these life transitions. The review will address the molecular and functional evolution of these axes and their interactions. Mechanisms of integration of internal and environmental cues, and activation of these neuroendocrine axes represent key questions in an “eco-evo-devo” perspective of metamorphosis. The roles played by developmental transitions in the innovation, adaptation, and plasticity of life cycles throughout vertebrates will be discussed. In the current context of global climate change and habitat destruction, the review will also address the impact of environmental factors, such as global warming and endocrine disruptors on hypothalamic-pituitary-thyroid and hypothalamic-pituitary-adrenal/interrenal axes, and regulation of developmental transitions.

Developmental programming of DNA methylation and gene expression patterns is associated with extreme cardiovascular tolerance to anoxia in the common snapping turtle

Background

Environmental fluctuation during embryonic and fetal development can permanently alter an organism’s morphology, physiology, and behaviour. This phenomenon, known as developmental plasticity, is particularly relevant to reptiles that develop in subterranean nests with variable oxygen tensions. Previous work has shown hypoxia permanently alters the cardiovascular system of snapping turtles and may improve cardiac anoxia tolerance later in life. The mechanisms driving this process are unknown but may involve epigenetic regulation of gene expression via DNA methylation. To test this hypothesis, we assessed in situ cardiac performance during 2 h of acute anoxia in juvenile turtles previously exposed to normoxia (21% oxygen) or hypoxia (10% oxygen) during embryogenesis. Next, we analysed DNA methylation and gene expression patterns in turtles from the same cohorts using whole genome bisulfite sequencing, which represents the first high-resolution investigation of DNA methylation patterns in any reptilian species.

Results

Genome-wide correlations between CpG and CpG island methylation and gene expression patterns in the snapping turtle were consistent with patterns observed in mammals. As hypothesized, developmental hypoxia increased juvenile turtle cardiac anoxia tolerance and programmed DNA methylation and gene expression patterns. Programmed differences in expression of genes such as SCN5A may account for differences in heart rate, while genes such as TNNT2 and TPM3 may underlie differences in calcium sensitivity and contractility of cardiomyocytes and cardiac inotropy. Finally, we identified putative transcription factor-binding sites in promoters and in differentially methylated CpG islands that suggest a model linking programming of DNA methylation during embryogenesis to differential gene expression and cardiovascular physiology later in life. Binding sites for hypoxia inducible factors (HIF1A, ARNT, and EPAS1) and key transcription factors activated by MAPK and BMP signaling (RREB1 and SMAD4) are implicated.

Conclusions

Our data strongly suggests that DNA methylation plays a conserved role in the regulation of gene expression in reptiles. We also show that embryonic hypoxia programs DNA methylation and gene expression patterns and that these changes are associated with enhanced cardiac anoxia tolerance later in life. Programming of cardiac anoxia tolerance has major ecological implications for snapping turtles, because these animals regularly exploit anoxic environments throughout their lifespan.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13072-021-00414-7.

The role of hormones and neurons in cardiomyocyte maturation

The heart undergoes profound morphological and functional changes as it continues to mature postnatally. However, this phase of cardiac development remains understudied. More recently, cardiac maturation research has attracted a lot of interest due to the need for more mature stem cell-derived cardiomyocytes for disease modeling, drug screening and heart regeneration. Additionally, neonatal heart injury models have been utilized to study heart regeneration, and factors regulating postnatal heart development have been associated with adult cardiac disease. Critical components of cardiac maturation are systemic and local biochemical cues. Specifically, cardiac innervation and the concentration of various metabolic hormones appear to increase perinatally and they have striking effects on cardiomyocytes. Here, we first report some of the key parameters of mature cardiomyocytes and then discuss the specific effects of neurons and hormonal cues on cardiomyocyte maturation. We focus primarily on the structural, electrophysiologic, metabolic, hypertrophic and hyperplastic effects of each factor. This review highlights the significance of underappreciated regulators of cardiac maturation and underscores the need for further research in this exciting field.

Single neonatal dexamethasone administration has long-lasting outcome on depressive-like behaviour, Bdnf, Nt-3, p75ngfr and sorting receptors (SorCS1-3) stress reactive expression

Elevated glucocorticoid level in the early postnatal period is associated with glucocorticoid therapy prescribed at preterm delivery most often has severe long-lasting neurodevelopmental and behavioural effects. Detailed molecular mechanisms of such programming action of antenatal glucocorticoids on behaviour are still poorly understood. To address this question we studied neurotrophins: Bdnf, Nt-3, Ngf and their receptors: p75ngfr, Sorcs3 expression changes after subcutaneous dexamethasone (DEX) 0.2 mg/kg injection to P2 rat pups. Neurotrophins expression level was studied in the hippocampus (HPC). Disturbances in these brain regions have been implicated in the emergence of multiple psychopathologies. p75ngfr and Sorcs3 expression was studied in the brainstem—region where monoamine neurons are located. Immunohistochemically P75NTR protein level changes after DEX were investigated in the brainstem Locus Coereleus norepinephrine neurons (NE). In the first hours after DEX administration elevation of neurotrophins expression in HPC and decline of receptor’s expression in the NE brainstem neurons were observed. Another critical time point during maturation is adolescence. Impact of elevated glucocorticoid level in the neonatal period and unpredictable stress (CMUS) at the end of adolescence on depressive-like behaviour was studied. Single neonatal DEX injection leads to decrease in depressive-like behaviour, observed in FST, independently from chronic stress. Neonatal DEX administration decreased Ntf3 and SorCS1 expression in the brainstem. Also Bdnf mRNA level in the brainstem of these animals didn’t decrease after FST. CMUS at the end of adolescence changed p75ngfr and SorCS3 expression in the brainstem in the animals that received single neonatal DEX administration.

Isolating adverse effects of glucocorticoids on the embryonic cardiovascular system

Antenatal glucocorticoid therapy reduces mortality in the preterm infant, but evidence suggests off-target adverse effects on the developing cardiovascular system. Whether deleterious effects are direct on the offspring or secondary to alterations in uteroplacental physiology is unclear. Here, we isolated direct effects of glucocorticoids using the chicken embryo, a model system in which the effects on the developing heart and circulation of therapy can be investigated, independent of effects on the mother and/or the placenta. Fertilized chicken eggs were incubated and divided randomly into control (C) or dexamethasone (Dex) treatment at day 14 out of the 21-day incubation period. Combining functional experiments at the isolated organ, cellular and molecular levels, embryos were then studied close to term. Chicken embryos exposed to dexamethasone were growth restricted and showed systolic and diastolic dysfunction, with an increase in cardiomyocyte volume but decreased cardiomyocyte nuclear density in the left ventricle. Underlying mechanisms included a premature switch from tissue accretion to differentiation, increased oxidative stress, and activated signaling of cellular senescence. These findings, therefore, demonstrate that dexamethasone treatment can have direct detrimental off-target effects on the cardiovascular system in the developing embryo, which are independent of effects on the mother and/or placenta.

Neonatal glucocorticoid overexposure alters cardiovascular function in young adult horses in a sex-linked manner

Prenatal glucocorticoid overexposure has been shown to programme adult cardiovascular function in a range of species, but much less is known about the long-term effects of neonatal glucocorticoid overexposure. In horses, prenatal maturation of the hypothalamus-pituitary-adrenal axis and the normal prepartum surge in fetal cortisol occur late in gestation compared to other precocious species. Cortisol levels continue to rise in the hours after birth of full-term foals and increase further in the subsequent days in premature, dysmature and maladapted foals. Thus, this study examined the adult cardiovascular consequences of neonatal cortisol overexposure induced by adrenocorticotropic hormone administration to full-term male and female pony foals. After catheterisation at 2-3 years of age, basal arterial blood pressures (BP) and heart rate were measured together with the responses to phenylephrine (PE) and sodium nitroprusside (SNP). These data were used to assess cardiac baroreflex sensitivity. Neonatal cortisol overexposure reduced both the pressor and bradycardic responses to PE in the young adult males, but not females. It also enhanced the initial hypotensive response to SNP, slowed recovery of BP after infusion and reduced the gain of the cardiac baroreflex in the females, but not males. Basal diastolic pressure and cardiac baroreflex sensitivity also differed with sex, irrespective of neonatal treatment. The results show that there is a window of susceptibility for glucocorticoid programming during the immediate neonatal period that alters cardiovascular function in young adult horses in a sex-linked manner.