Placental insufficiency results in temporal alterations in the renin angiotensin system in male hypertensive growth restricted offspring

How the kidney is impacted by the perinatal maternal environment to develop hypertension

Environmental conditions during perinatal development such as maternal undernutrition, maternal glucocorticoids, placental insufficiency, and maternal sodium overload can program changes in renal Na(+) excretion leading to hypertension. Experimental studies indicate that fetal exposure to an adverse maternal environment may reduce glomerular filtration rate by decreasing the surface area of the glomerular capillaries. Moreover, fetal responses to environmental insults during early life that contribute to the development of hypertension may include increased expression of tubular apical or basolateral membrane Na(+) transporters and increased production of renal superoxide leading to enhanced Na(+) reabsorption. This review will address the role of these potential renal mechanisms in the fetal programming of hypertension in experimental models induced by maternal undernutrition, fetal exposure to glucocorticoids, placental insufficiency, and maternal sodium overload in the rat.

Preterm birth and neurodevelopment: a review of outcomes and recommendations for early identification and cost-effective interventions

This review summarizes research findings to date on neurological and health outcomes following preterm birth, tools to identify children at risk for neurodevelopmental impairment and interventions to prevent preterm birth and improve outcomes. We bring together findings from research in high- and low-income countries, with an aim to provide a global perspective on the issues. Around the world, preterm birth is rising in importance as a cause of under-five morbidity and mortality, and we project that this trend will continue over time, particularly given the lack of interventions to prevent the condition. With the development of improved screening instruments, further identification and scale up of cost-effective interventions to optimize early childhood development and accelerated research on the underlying biological mechanisms, we have an opportunity to reduce rates of neurodevelopmental impairment, particularly in countries with the highest burden.

Sex differences in the enhanced responsiveness to acute angiotensin II in growth-restricted rats: role of fasudil, a Rho kinase inhibitor

This study tested the hypothesis that Rho kinase contributes to the enhanced pressor response to acute angiotensin II in intact male growth-restricted and gonadectomized female growth-restricted rats. Mean arterial pressure (MAP) and renal function were determined in conscious animals pretreated with enalapril (250 mg/l in drinking water) for 1 wk to block the endogenous renin-angiotensin system and normalize blood pressure (baseline). Blood pressure and renal hemodynamics did not differ at baseline. Acute Ang II (100 ng·kg(-1)·min(-1)) induced a greater increase in MAP and renal vascular resistance and enhanced reduction in glomerular filtration rate in intact male growth-restricted rats compared with intact male controls (P < 0.05). Cotreatment with the Rho kinase inhibitor fasudil (33 μg·kg(-1)·min(-1)) significantly attenuated these hemodynamic changes (P < 0.05), but it did not abolish the differential increase in blood pressure above baseline, suggesting that the impact of intrauterine growth restriction on blood pressure in intact male growth-restricted rats is independent of Rho kinase. Gonadectomy in conjunction with fasudil returned blood pressure back to baseline in male growth-restricted rats, and yet glomerular filtration rate remained significantly reduced (P < 0.05). Thus, these data suggest a role for enhanced renal sensitivity to acute Ang II in the developmental programming of hypertension in male growth-restricted rats. However, inhibition of Rho kinase had no effect on the basal or enhanced increase in blood pressure induced by acute Ang II in the gonadectomized female growth-restricted rat. Therefore, these studies suggest that Rho kinase inhibition exerts a sex-specific effect on blood pressure sensitivity to acute Ang II in growth-restricted rats.

Epigenetics and developmental programming of adult onset diseases

Maternal perturbations or sub-optimal conditions during development are now recognized as contributing to the onset of many diseases manifesting in adulthood. This "developmental programming" of disease has been explored using animal models allowing insights into the potential mechanisms involved. Impaired renal development, resulting in a low nephron number, has been identified as a common outcome that is likely to contribute to the development of hypertension in the offspring as adults. Changes in other organs and systems, including the heart and the hypothalamic–pituitary–adrenal axis, have also been found. Evidence has recently emerged suggesting that epigenetic changes may occur as a result of developmental programming and result in permanent changes in the expression patterns of particular genes. Such epigenetic modifications may be responsible not only for an increased susceptibility to disease for an individual, but indirectly for the establishment of a disease state in a subsequent generation. Further research in this field, particularly examination as to whether epigenetic changes to genes affecting kidney development do occur, are essential to understanding the underlying mechanisms of developmental programming of disease.

Developmental programming of hypertension and kidney disease

A growing body of evidence supports the concept that changes in the intrauterine milieu during "sensitive" periods of embryonic development or in infant diet after birth affect the developing individual, resulting in general health alterations later in life. This phenomenon is referred to as "developmental programming" or "developmental origins of health and disease." The risk of developing late-onset diseases such as hypertension, chronic kidney disease (CKD), obesity or type 2 diabetes is increased in infants born prematurely at <37 weeks of gestation or in low birth weight (LBW) infants weighing <2,500 g at birth. Both genetic and environmental events contribute to the programming of subsequent risks of CKD and hypertension in premature or LBW individuals. A number of observations suggest that susceptibility to subsequent CKD and hypertension in premature or LBW infants is mediated, at least in part, by reduced nephron endowment. The major factors influencing in utero environment that are associated with a low final nephron number include uteroplacental insufficiency, maternal low-protein diet, hyperglycemia, vitamin A deficiency, exposure to or interruption of endogenous glucocorticoids, and ethanol exposure. This paper discusses the effect of premature birth, LBW, intrauterine milieu, and infant feeding on the development of hypertension and renal disease in later life as well as examines the role of the kidney in developmental programming of hypertension and CKD.

Role of angiotensin II in arterial pressure and renal hemodynamics in rats with altered renal development: age- and sex-dependent differences

Numerous studies have demonstrated that angiotensin II (ANG II) is involved in hypertension and renal changes occurring as a consequence of an adverse event during renal development. However, it was unknown whether this involvement is sex and age dependent. This study examines whether the increments in arterial pressure (AP) and in the renal sensitivity to ANG II are sex and age dependent in rats with altered renal development. It also evaluates whether the ANG II effects are accompanied by increments in AT(1) receptors and oxidative stress. Experiments were performed in 3- to 4- and 10- to 11-mo-old rats treated with vehicle or an AT(1) receptor antagonist (ARAnp) during the nephrogenic period. ARAnp-treated rats were hypertensive, but an age-dependent rise in AP was only found in males. Three days of treatment with candesartan (7 mg·kg(-1)·day(-1)) led to a fall of AP that was greater (P < 0.05) in male than in female 10- to 11-mo-old ARAnp-treated rats. Oxidated proteins were elevated (P < 0.05), and the decrease in AP elicited by candesartan was reduced (P < 0.05) when these rats are also treated with tempol (18 mg·kg(-1)·day(-1)). Hypertension was not maintained by an elevation of AT(1) receptors in kidneys and mesenteric arteries. The acute renal hemodynamic response to ANG II (30 ng·kg(-1)·min(-1)) was similarly enhanced (P < 0.05) in both sexes of ARAnp-treated rats at 3-4 but not at 10-11 mo of age. Our results suggest that an adverse event during the nephrogenic period induces an ANG II-dependent increment in AP that is aggravated only in males during aging and that oxidative stress but not an increase in AT(1) receptor contributes to the rise in AP. This study also shows that the renal hemodynamic sensitivity to ANG II is transitorily enhanced in both sexes of rats with altered renal development.

Renin is activated in monochorionic diamniotic twins with birthweight discordance who do not have twin-to-twin transfusion syndrome

OBJECTIVE

To assess renin, aldosterone, human atrial natriuretic peptide (hANP) and brain natriuretic peptide (BNP) levels in cord blood from monochorionic diamniotic (MD) twins with a birthweight (BW) discordance that do not satisfy the criteria of twin-to-twin transfusion syndrome (TTTS).

STUDY DESIGN

Cord blood samples were obtained from 28 MD twins without TTTS. They were divided into two groups on the basis of BW discordance as follows: large (>7.5%) and small (7.5%). Cord blood renin, aldosterone, hANP and BNP levels were measured.

RESULT

Renin levels in MD twins with a large BW discordance were significantly higher than those in MD twins with a small BW discordance, with no significant differences in aldosterone, hANP and BNP levels. A significant correlation was found between renin levels and BW discordance.

CONCLUSION

Renin is activated in MD twins with a BW discordance of >7.5%, even in non-TTTS.

Influence of birth weight on the renal development and kidney diseases in adulthood: experimental and clinical evidence

Several clinical and experimental studies support the hypothesis that foetal programming is an important determinant of nephropathy, hypertension, coronary heart disease, and type 2 diabetes during adulthood. In this paper, the renal repercussions of foetal programming are emphasised, and the physiopathological mechanisms are discussed. The programming of renal diseases is detailed based on the findings of kidney development and functional parameters.

Pre-eclampsia and offspring cardiovascular health: mechanistic insights from experimental studies

Pre-eclampsia is increasingly recognized as more than an isolated disease of pregnancy. Women who have had a pregnancy complicated by pre-eclampsia have a 4-fold increased risk of later cardiovascular disease. Intriguingly, the offspring of affected pregnancies also have an increased risk of higher blood pressure and almost double the risk of stroke in later life. Experimental approaches to identify the key features of pre-eclampsia responsible for this programming of offspring cardiovascular health, or the key biological pathways modified in the offspring, have the potential to highlight novel targets for early primary prevention strategies. As pre-eclampsia occurs in 2–5% of all pregnancies, the findings are relevant to the current healthcare of up to 3 million people in the U.K. and 15 million people in the U.S.A. In the present paper, we review the current literature that concerns potential mechanisms for adverse cardiovascular programming in offspring exposed to pre-eclampsia, considering two major areas of investigation: first, experimental models that mimic features of the in utero environment characteristic of pre-eclampsia, and secondly, how, in humans, offspring cardiovascular phenotype is altered after exposure to pre-eclampsia. We compare and contrast the findings from these two bodies of work to develop insights into the likely key pathways of relevance. The present review and analysis highlights the pivotal role of long-term changes in vascular function and identifies areas of growing interest, specifically, response to hypoxia, immune modification, epigenetics and the anti-angiogenic in utero milieu.

Birth weight is inversely associated with blood pressure and serum aldosterone and cortisol levels in children

CONTEXT

Low birth weight has been independently associated with adult hypertension, and renin-angiotensin system (RAS) plays a role in this connection.

OBJECTIVE

To characterize the associations between birth weight (BW) and serum aldosterone (SA), serum cortisol, plasma renin activity (PRA) and blood pressure (BP).

DESIGN

Cross-sectional study.

SUBJECTS

Children from the community born at a gestational age >32 weeks.

METHODS

Systolic and diastolic BP indices (SBPi and DBPi) were calculated using the observed BP/50th percentile BP for gender, age and stature. BW was transformed to a standard deviation score (SDS) for gestational age, whereas SA, serum cortisol and PRA were transformed using the natural log.

RESULTS

We selected 288 subjects between the ages of 4·9 and 15·5 years (Females, 50%). After adjusting for body mass index (BMI) SDS and Tanner, multiple regression analysis revealed that BW (SDS) was both independently and inversely associated with the natural log of SA (β = -0·065; P = 0·039), the natural log of serum cortisol (β = -0·064; P = 0·009), SBPi (β = -0·012; P = 0·020) and DBPi (β = -0·023; P = 0·002). An association was not observed with PRA (P = 0·178) and aldosterone renin ratio (ARR) (P = 0·452). Serum cortisol levels were positively associated with SA (r = 0·125; P = 0·034), while an association with PRA (P = 0·251) and ARR (P = 0·052) was not observed.

CONCLUSIONS

The results of this study demonstrate an inverse association between birth weight and blood pressure and serum aldosterone and cortisol levels. This association is independent of BMI and Tanner, suggesting foetal programming of the hypothalamic-pituitary-adrenal axis.

Protein restriction to pregnant rats increases the plasma levels of angiotensin II and expression of angiotensin II receptors in uterine arteries

Whether gestational protein restriction affects the renin-angiotensin system (RAS) in uterine artery remains unknown. In this study, we hypothesized that gestational protein restriction alters the expression of RAS components in uterine artery. In study one, time-scheduled pregnant Sprague Dawley rats were fed a normal or low-protein (LP) diet from Day 3 of pregnancy until they were killed at Days 19 and 22. The uterine arteries were collected and used for gene expression of Ace, Ace2, Agtr1a, Agtr1b, Agtr2, Esr1, and Esr2 by quantitative real-time PCR and/or Western blotting. LP increased plasma levels of angiotensin II in pregnant rats. In the uterine artery, the expressions of Agtr1a, Agtr1b, and Esr1 were increased by LP at Days 19 and 22 of pregnancy, whereas the abundance of AGTR1 and AGTR2 was increased by LP at Day 19 of pregnancy. The expression of Ace2 was not detectable in rat uterine artery. In study two, virgin female rats were ovariectomized and implanted with either 17beta-estradiol (E2), progesterone (P4), both E2 and P4, or placebo pellets until they were killed 7 days later. In rat uterine artery, E2 and P4 reduced the expression of Agtr1a, and E2 increased the expression of Agtr1b and Agtr2, but neither E2 nor P4 regulated the expression of Ace. These results indicate that gestational protein restriction induces an increase in Agtr1 expression in uterine artery, and thus may exacerbate the vasoconstriction to elevated angiotensin II present in maternal circulation, and that female sex hormones also play a role in this process.

Maternal protein restriction reduces expression of angiotensin I-converting enzyme 2 in rat placental labyrinth zone in late pregnancy

Both the systemic and the uteroplacental renin-angiotensin system (RAS) display dramatic changes during pregnancy. However, whether gestational protein insufficiency affects the expressions of RAS in the placenta remains unknown. In this study, we hypothesized that the expression of Ace2 in the placental labyrinth was reduced by maternal protein restriction. Pregnant Sprague-Dawley rats were fed a normal diet or a low-protein diet (LP) from Day 1 of pregnancy until they were killed at Day 14 or Day 18. The labyrinth zone (LZ) of the placenta was then dissected and snap frozen for expression analysis by quantitative real-time PCR of Ace, Ace2, Agtr1a, Agtr1b, and Agtr2. Formalin-fixed placentas were used for immunohistochemical analysis on ACE and ACE2 proteins. The findings include 1) the expression of Ace2 in rat LZ was reduced by maternal protein restriction in late pregnancy; 2) ACE protein was mainly present in syncytiotrophoblasts, whereas ACE2 protein was found predominantly in fetal mesenchymal tissue and fetal capillaries; 3) Agtr1a was predominant in the rat LZ, and its mRNA levels, but not protein levels, were reduced by LP; 4) expressions of Ace, Ace2, and Agtr1a in the rat LZ and their response to LP occurred in a gender-dependent manner. These results may indicate that a reduced expression of Ace2 and perhaps an associated reduction in angiotensin (1-7) production in the placenta by maternal protein restriction may be responsible for fetal growth restriction and associated programming of adulthood hypertension.

Circulating and utero-placental adaptations to chronic placental ischemia in the rat

While utero-placental insufficiency is associated with adverse outcomes for both mother and fetus, many of the maternal-fetal adaptations during pregnancy in models of fetal compromise remain unclear. The purpose of this study was to determine if chronically reduced uterine perfusion pressure (RUPP) during days 14-19 of gestation alters feto-placental growth differentially from the cervical to ovarian ends of the uterus and generates metabolic adaptations such as increased blood lactate (BLa) concentrations and lactate transporter expression in the placenta. Fetal growth restriction was evident, placental efficiency (fetal weight/placental weight) decreased (4.7 ± 0.35 vs. 5.9 ± 0.30; P < 0.05) and fetal growth pattern within the uterus was altered in the RUPP compared to the normal pregnant (NP) rats. Blood lactate concentrations were increased (3.3 ± 0.3 vs. 2.1 ± 0.4 mmol/l; P < 0.05) in NP compared to virgin rats, and in RUPP compared to NP (5.0 ± 0.6 vs. 3.3 ± 0.3 mmol/l; P < 0.05). Lactate concentration was increased (10.0 ± 0.6 vs. 7.1 ± 0.8 mmol/l; P < 0.05) in the media from hypoxic compared to normoxic BeWo cells. No changes in expression of placental MCT1, 2, or 4 were observed between RUPP and NP rats. RUPP resulted in decreased plasma leptin (2.0 ± 0.3 vs. 3.1 ± 0.4; P < 0.05) but no change in IGF-1 compared to NP. The present data indicate chronic placental ischemia results in numerous endocrine and metabolic changes during late pregnancy in the rat and that the RUPP model has differential effects on fetal growth depending on uterine position.

Prenatal programming of hypertension in the rat: effect of postnatal rearing

Background/Aims

Dietary protein deprivation during pregnancy causes hypertension in offspring when they become adults. This study examined if postnatal rearing had an effect on blood pressure and glomerular number in male rats whose mothers were fed either a control diet or a low protein diet.

Methods

Neonates were cross fostered at 1 day of age to a different mother. After birth, all nursing and weaned rats were fed a control diet. Blood pressure and glomerular number were measured in adult offspring.

Results

Control rats cross fostered to another control mother had a lower blood pressure than low protein rats cross fostered to another low protein mother (133 ± 4 vs. 151 ± 4 mm Hg, p < 0.05) and a greater number of glomeruli (28,388 ± 989 vs. 25,045 ± 851, p < 0.05). Fostering pups from the 20% group to mothers that were fed a 6% diet during pregnancy did not cause hypertension or a reduction in the number of glomeruli. However, fostering the 6% group on to mothers that were fed a 20% protein diet during pregnancy resulted in normalization of the blood pressure and number of glomeruli.

Conclusion

The hypertension and reduced glomerular number resulting from prenatal dietary protein deprivation can be normalized by improving the postnatal environment.

Hypersensitivity to acute ANG II in female growth-restricted offspring is exacerbated by ovariectomy

Female growth-restricted offspring are normotensive in adulthood. However, ovariectomy induces a marked increase in mean arterial pressure (MAP) that is abolished by renin angiotensin system (RAS) blockade, suggesting RAS involvement in the etiology of hypertension induced by ovariectomy in adult female growth-restricted offspring. Blockade of the RAS also abolishes hypertension in adult male growth-restricted offspring. Moreover, sensitivity to acute ANG II is enhanced in male growth-restricted offspring. Thus, we hypothesized that an enhanced sensitivity to acute ANG II may contribute to hypertension induced by ovariectomy in female growth-restricted offspring. Female offspring were subjected to ovariectomy (OVX) or sham ovariectomy (intact) at 10 wk of age. Cardio-renal hemodynamic parameters were determined before and after an acute infusion of ANG II (100 ng·kg(-1)·min(-1) for 30 min) at 16 wk of age in female offspring pretreated with enalapril (40 mg·kg(-1)·day(-1) for 7 days). Acute ANG II induced a significant increase in MAP in intact growth-restricted offspring (155 ± 2 mmHg, P < 0.05) relative to intact control (145 ± 4 mmHg). Ovariectomy augmented the pressor response to ANG II in growth-restricted offspring (163 ± 2 mmHg, P < 0.05), with no effect in control (142 ± 2 mmHg). Acute pressor responses to phenylephrine did not differ in growth-restricted offspring relative to control, intact, or ovariectomized. Furthermore, renal hemodynamic responses to acute ANG II were significantly enhanced only in ovariectomized female growth-restricted offspring. Thus, these data suggest that enhanced responsiveness to acute ANG II is programmed by intrauterine growth restriction and that sensitivity to acute ANG II is modulated by ovarian hormones in female growth-restricted offspring.

Fetal uninephrectomy in male sheep alters the systemic and renal responses to angiotensin II infusion and AT1R blockade

Fetal uninephrectomy (uni-x) at 100 days of gestation results in compensatory nephrogenesis in the remaining kidney, resulting in a 30% reduction in total nephron number in male sheep. Recently, we showed that uni-x males at 6 mo of age have elevated arterial pressure, reduced renal blood flow (RBF), glomerular filtration rate (GFR), and low plasma renin levels (Singh R, Denton K, Bertram J, Jefferies A, Head G, Lombardo P, Schneider-Kolsky M, Moritz K. J Hypertens 27: 386–396, 2009; Singh R, Denton K, Jefferies A, Bertram J, Moritz K. Clin Sci (Lond) 118: 669–680, 2010). We hypothesized this was due to upregulation of the intrarenal renin-angiotensin system (RAS). In this study, renal responses to ANG II infusion and ANG II type 1 receptor (AT1R) blockade were examined in the same 6-mo-old male sheep. Uni-x animals had reduced levels of renal tissue and plasma renin and ANG II. Renal gene expression of renin, and gene and protein levels of AT1R and AT2R, were significantly lower in uni-x animals. In response to graded ANG II infusion, sham animals had the expected decrease in conscious RBF and GFR. Interestingly, the response was biphasic in uni-x sheep, with GFR initially decreasing, but then increasing at higher ANG II doses (34 ± 7%; Pgroup × treatment < 0.001), due to a paradoxical decrease in renal vascular resistance ( Pgroup × treatment < 0.001). In response to AT1R blockade, while GFR and RBF responded similarly between groups, there was a marked increase in sodium excretion in uni-x compared with sham sheep (209 ± 35 vs. 25 ± 12%; P < 0.001). In conclusion, in 6-mo-old male sheep born with a single kidney, these studies demonstrate that this is a low-renin form of hypertension, in which responses to ANG II are perturbed and the intrarenal RAS is downregulated.

Cognitive function after intrauterine growth restriction and very preterm birth

OBJECTIVE

To evaluate the effects of intrauterine growth restriction (IUGR) with absent or reversed end-diastolic blood flow in the umbilical artery and very preterm birth on cognitive outcome at 5 to 8 years of age.

METHODS

We studied 34 children with IUGR born at a median of 26.9 gestational weeks (GWs) (range: 24-29 GWs) (PT-IUGR), 34 matched preterm appropriate-for-gestational age (PT-AGA) children, and 34 term AGA children (T-AGA) by using the Wechsler Preschool and Primary Scale of Intelligence, Wechsler Intelligence Scale for Children, Strengths and Difficulties Questionnaire, and Brown's attention-deficit disorder (ADD) scales.

RESULTS

The PT-IUGR group had mean (SD) scores on the verbal IQ (VIQ) and full-scale IQ (FSIQ) of 83.8 (17.3) and 78.9 (16.6), respectively, compared with the PT-AGA group, which had scores of 96.0 (14.5) and 90.1 (14.2) (P = .003 and P < .007), and the T-AGA group, which had scores of 101.3 (12) and 102.9 (13.2) (P < .001 and P < 001), respectively. The VIQ difference remained significant after adjustment for parental level of education, gestational age at birth, and neonatal morbidity. Performance IQ (PIQ) did not differ between the PT-IUGR and PT-AGA groups; their mean PIQs were lower than that of the T-AGA group (P < .001). Boys in the PT-IUGR group scored lower than girls in VIQ and FSIQ (P = .005 and .007, respectively). Behavior and ADD scores did not differ between the preterm groups.

CONCLUSIONS

Children born very preterm after IUGR have an increased risk for cognitive impairment at early school age compared with children delivered very preterm for other reasons. Differences in cognitive outcome were restricted to boys who may have been especially vulnerable to the influence of IUGR and very preterm birth.

Renal programming: cause for concern?

Development of the kidney can be altered in utero in response to a suboptimal environment. The intrarenal factors that have been most well characterized as being sensitive to programming events are kidney mass/nephron endowment, the renin-angiotensin system, tubular sodium handling, and the renal sympathetic nerves. Newborns that have been subjected to an adverse intrauterine environment may thus begin life at a distinct disadvantage, in terms of renal function, at a time when the kidney must take over the primary role for extracellular fluid homeostasis from the placenta. A poor beginning, causing renal programming, has been linked to increased risk of hypertension and renal disease in adulthood. However, although a cause for concern, increasingly, evidence demonstrates that renal programming is not a fait accompli in terms of future cardiovascular and renal disease. A greater understanding of postnatal renal maturation and the impact of secondary factors (genes, sex, diet, stress, and disease) on this process is required to predict which babies are at risk of increased cardiovascular and renal disease as adults and to be able to devise preventative measures.

Enhanced sensitivity to acute angiotensin II is testosterone dependent in adult male growth-restricted offspring

Placental insufficiency results in intrauterine growth restriction (IUGR) and hypertension in adult male growth-restricted rats. Although renal ANG II and plasma renin activity do not differ between growth-restricted and control rats, blockade of the renin-angiotensin system (RAS) abolishes hypertension in growth-restricted rats, suggesting that the RAS contributes to IUGR-induced hypertension. Moreover, castration abolishes hypertension in growth-restricted rats, indicating an important role for testosterone. Therefore, we hypothesized that enhanced responsiveness to ANG II contributes to hypertension in this model of IUGR and that androgens may play a pivotal role in this enhanced response. Physiological parameters were determined at 16 wk of age in male rats pretreated with enalapril (40 mg.kg(-1).day(-1)) for 1 wk. Baseline blood pressures were similar between growth-restricted (112 +/- 3 mmHg) and control (110 +/- 2 mmHg) rats; however, an enhanced pressor response to acute ANG II (100 ng.kg(-1).min(-1) for 30 min) was observed in growth-restricted (160 +/- 2 mmHg) vs. control (136 +/- 2 mmHg; P < 0.05) rats. Castration abolished the enhanced pressor response to acute ANG II in growth-restricted (130 +/- 2 mmHg) rats with no significant effect on blood pressure in controls (130 +/- 2 mmHg). Blood pressure was increased to a similar extent above baseline in response to acute phenylephrine (100 microg/min) in control (184 +/- 5 mmHg) and growth-restricted (184 +/- 8 mmHg) rats, suggesting the enhanced pressor response in growth-restricted rats is ANG II specific. Thus, these results suggest that growth-restricted rats exhibit an enhanced responsiveness to ANG II that is testosterone dependent and indicate that the RAS may serve as an underlying mechanism in mediating hypertension programmed in response to IUGR.

Mechanisms involved in the developmental programming of adulthood disease

There are many instances in life when the environment plays a critical role in the health outcomes of an individual, yet none more so than those experienced in fetal and neonatal life. One of the most detrimental environmental problems encountered during this critical growth period are changes in nutrition to the growing fetus and newborn. Disturbances in the supply of nutrients and oxygen to the fetus can not only lead to adverse fetal growth patterns, but they have also been associated with the development of features of metabolic syndrome in adult life. This fetal response has been termed developmental programming or the developmental origins of health and disease. The present review focuses on the epidemiological studies that identified this association and the importance that animal models have played in studying this concept. We also address the potential mechanisms that may underpin the developmental programming of future disease. It also highlights (i) how developmental plasticity, although beneficial for short-term survival, can subsequently programme glucose intolerance and insulin resistance in adult life by eliciting changes in key organ structures and the epigenome, and (ii) how aberrant mitochondrial function can potentially lead to the development of Type 2 diabetes and other features of metabolic syndrome.

Effect of prenatal dexamethasone on postnatal serum and urinary angiotensin II levels

BACKGROUND

Prenatal programming of hypertension has been described in humans and in animal models that receive a prenatal insult, but the mechanism for the increase in blood pressure remains elusive.

METHODS

In male rats whose mothers received dexamethasone between days 15 and 18 of gestation systemic and urinary levels of angiotensin II were measured to determine whether angiotensin II was a potential factor for the generation (4 weeks of age) or maintenance (8 weeks of age) of hypertension.

RESULTS

A group 4- and 8-week-old male rats that were the product of a pregnancy where the mother received prenatal dexamethasone between days 15 and 18 of gestation had comparable plasma renin and angiotensin II levels to the offspring of vehicle-treated controls. Renal angiotensin II levels were not different at 4 and 8 weeks of age between the controls and the prenatal dexamethasone group. Urine angiotensin II/Creatinine levels, a reflection of filtered and renally generated and secreted angiotensin II, were higher at both 4 and 8 weeks of age in male rats that received prenatal dexamethasone compared to controls.

CONCLUSIONS

The high-urine angiotensin II levels in prehypertensive and hypertensive rats that were the product of mothers that received dexamethasone compared to vehicle suggest that luminal angiotensin II may play a role in the generation and maintenance of hypertension in this model of prenatal programming.

The clinical importance of nephron mass

Abundant evidence supports the association between low birth weight (LBW) and renal dysfunction in humans. Anatomic measurements of infants, children, and adults show significant inverse correlation between LBW and nephron number. Nephron numbers are also lower in individuals with hypertension compared with normotension among white and Australian Aboriginal populations. The relationship between nephron number and hypertension among black individuals is still unclear, although the high incidence of LBW predicts low nephron number in this population as well. LBW, a surrogate for low nephron number, also associates with increasing BP from childhood to adulthood and increasing risk for chronic kidney disease in later life. Because nephron numbers can be counted only postmortem, surrogate markers such as birth weight, prematurity, adult height, reduced renal size, and glomerulomegaly are potentially useful for risk stratification, for example, during living-donor assessment. Because early postnatal growth also affects subsequent risk for higher BP or reduced renal function, postnatal nutrition, a potentially modifiable factor, in addition to intrauterine effects, has significant influence on long-term cardiovascular and renal health.

Review: Sex specific programming: a critical role for the renal renin-angiotensin system

The "Developmental Origins of Health and Disease" hypothesis has caused resurgence of interest in understanding the factors regulating fetal development. A multitude of prenatal perturbations may contribute to the onset of diseases in adulthood including cardiovascular and renal diseases. Using animal models such as maternal glucocorticoid exposure, maternal calorie or protein restriction and uteroplacental insufficiency, studies have identified alterations in kidney development as being a common feature. The formation of a low nephron endowment may result in impaired renal function and in turn may contribute to disease. An interesting feature in many animal models of developmental programming is the disparity between males and females in the timing of onset and severity of disease outcomes. The same prenatal insult does not always affect males and females in the same way or to the same degree. Recently, our studies have focused on changes induced in the kidney of both the fetus and the offspring, following a perturbation during pregnancy. We have shown that changes in the renin-angiotensin system (RAS) occur in the kidney. The changes are often sex specific which may in part explain the observed sex differences in disease outcomes and severity. This review explores the evidence suggesting a critical role for the RAS in sex specific developmental programming of disease with particular reference to the immediate and long term changes in the local RAS within the kidney.

Role of the kidney in the prenatal and early postnatal programming of hypertension

Epidemiologic studies from several different populations have demonstrated that prenatal insults, which adversely affect fetal growth, result in an increased incidence of hypertension when the offspring reaches adulthood. It is now becoming evident that low-birth-weight infants are also at increased risk for chronic kidney disease. To determine how prenatal insults result in hypertension and chronic kidney disease, investigators have used animal models that mimic the adverse events that occur in pregnant women, such as dietary protein or total caloric deprivation, uteroplacental insufficiency, and prenatal administration of glucocorticoids. This review examines the role of the kidney in generating and maintaining an increase in blood pressure in these animal models. This review also discusses how early postnatal adverse events may have repercussions in later life. Causes for the increase in blood pressure by perinatal insults are likely multifactorial and involve a reduction in nephron number, dysregulation of the systemic and intrarenal renin-angiotensin system, increased renal sympathetic nerve activity, and increased tubular sodium transport. Understanding the mechanism for the increase in blood pressure and renal injury resulting from prenatal insults may lead to therapies that prevent hypertension and the development of chronic kidney and cardiovascular disease.

Programming of hypertension: associations of plasma aldosterone in adult men and women with birthweight, cortisol, and blood pressure

Animal models suggest that explanations for the association of low birthweight with adult hypertension may include chronic activation of the hypothalamic-pituitary-adrenal or renin-angiotensin-aldosterone axes. In humans, low birthweight predicts elevated plasma cortisol, but associations with aldosterone have not been reported. We measured aldosterone in serum samples from 205 men and 106 women from 67 to 78 years of age, from Hertfordshire, UK, for whom birthweight was recorded. Participants underwent an overnight low-dose (0.25 mg) dexamethasone suppression test and a low-dose (1 mug) ACTH (corticotropin) stimulation test and were genotyped for the -344 C/T polymorphism of the CYP11B2 gene encoding aldosterone synthase. Median aldosterone was 6.22 ng/dL (range 0.15 to 38.74) and was higher in men than women (P<0.0001). Higher aldosterone levels after both dexamethasone and ACTH stimulation were associated with higher blood pressure (r=0.20, P=0.001; r=0.33, P<0.0001, respectively) and with lower birthweight (r=-0.16, P=0.008; r=-0.21, P=0.001, respectively). These associations remained significant after adjusting for age, gender, obesity, and genotype. Our findings supplement previous evidence that aldosterone is an important regulator of blood pressure and suggest that factors in early life that retard fetal growth and program activation of the hypothalamic-pituitary-adrenal axis in humans result not only in higher glucocorticoid activity but also in increased mineralocorticoid activity.

Prenatal nutrition: a critical window of opportunity for mother and child

The prenatal period encompasses a critical window for future health and functioning of mother and child. Attention previously focused on undernutrition risk (i.e., in developing countries and famine conditions) shifted to mismatch between prenatal 'programming' by undernutrition and postnatal overconsumption (i.e., low birthweight vs rapid postnatal growth), now to overconsumption/overweight throughout the reproductive cycle and short- and long-term health risks, including obesity, diabetes, dyslipidemia and cardiovascular disease. Moreover, overconsumption/overweight do not guarantee adequacy of critical nutrients (i.e., against birth defects or for brain development). Multinutrient supplementation - including zinc, iodine, choline and long-chain polyunsaturated fatty acids, especially n-3 - may have advantages over single-nutrient supplements, for example, iron or folate. Future nutritional care for healthy in utero programming may necessitate individual assessment and follow-up, including preconception nutritional preparation, appropriate weight gain, metabolic balance and food-based regimens enhanced by key nutrient fortification and/or supplementation, warranting further research into nutritional optimization of pregnancy outcomes.

Alterations in circulatory and renal angiotensin-converting enzyme and angiotensin-converting enzyme 2 in fetal programmed hypertension

Antenatal betamethasone treatment is a widely accepted therapy to accelerate lung development and improve survival in preterm infants. However, there are reports that infants who receive antenatal glucocorticoids exhibit higher systolic blood pressure in their early adolescent years. We have developed an experimental model of programming whereby the offspring of pregnant sheep administered clinically relevant doses of betamethasone exhibit elevated blood pressure. We tested the hypothesis as to whether alterations in angiotensin-converting enzyme (ACE), ACE2, and neprilysin in serum, urine, and proximal tubules are associated with this increase in mean arterial pressure. Male sheep were administered betamethasone (2 doses of 0.17 mg/kg, 24 hours apart) or vehicle at the 80th day of gestation and delivered at term. Sheep were instrumented at adulthood (1.8 years) for direct conscious recording of mean arterial pressure. Serum and urine were collected and proximal tubules isolated from the renal cortex. Betamethasone-treated animals had elevated mean arterial pressure (97+/-3 versus 83+/-2 mm Hg; P<0.05) and a 25% increase in serum ACE activity (48.4+/-7.0 versus 36.0+/-2.7 fmol/mL per minute) but a 40% reduction in serum ACE2 activity (18.8+/-1.2 versus 31.4+/-4.4 fmol/mL per minute). In isolated proximal tubules, ACE2 activity and expression were 50% lower in the treated sheep with no significant change in ACE or neprilysin activities. We conclude that antenatal steroid treatment results in the chronic alteration of ACE and ACE2 in the circulatory and tubular compartments, which may contribute to the higher blood pressure in this model of fetal programming-induced hypertension.

Sex differences in the developmental origins of hypertension and cardiorenal disease

The "developmental origins of health and disease" (DOHAD) hypothesis derives from clinical observations, indicating long-term health consequences for persons of low birth weight. There is growing evidence, primarily from animal studies, that supports the idea that processes put in motion during development that contribute to DOHAD do not necessarily reflect as significantly compromised growth and altered birth weight. Throughout the body of work investigating the DOHAD hypothesis, several themes have emerged; the importance of the placenta, the presence of critical periods of vulnerability, the involvement of the kidney in programmed hypertension, the presence of sex differences in the progression and development of adult diseases. Despite compelling findings in recent studies, much remains unclear regarding the impact of biological sex in the progression of human diseases, in general, and in the mechanisms underlying developmentally programmed responses, in particular. Although the contribution of biological sex to DOHAD is increasingly recognized, it also appears that it may exert distinctly different influences during fetal and adult life. The mechanisms by which biological sex contributes to these processes remains nebulous at present; nevertheless, several intriguing mechanistic candidates have been proposed ranging from differences in the amounts of sex hormones (e.g., estrogens, androgens) to recently described sexual dimorphism in the transcriptome of a variety of mammalian tissues. Recognizing the influences of biological sex or sex hormones on DOHAD uniquely situates research in this area to provide significant insights into the development and progression of many diseases, recent examples of which are the subject of this review.

Developmental programming of hypertension: insight from animal models of nutritional manipulation

Hypertension is a multi-factorial disorder thought to result from both genetic and environmental factors. Epidemiological studies suggest that cardiovascular diseases such as hypertension may be programmed in-utero . Experimental studies demonstrate that developmental programming occurs in response to a nutritional insult during fetal life and leads to slow fetal growth and permanent structural and pathophysiological changes that result in the development of hypertension and cardiovascular disease. A reduction in nephron number, hyperfiltration and increased susceptibility to renal injury, activation of the sympathetic and renin angiotensin systems, in addition to, increases in oxidative stress, are potential mediators of post-natal hypertension programmed in response to developmental insult. However, the quantitative importance and integration of these mechanistic pathways has not been clearly elucidated. Additionally, animal models of developmental programming exhibit sex differences with severity of the fetal insult critical to the phenotypic outcome. Recent studies suggest that sex hormones may play a critical role via modulation of the normal regulatory systems involved in the long-term control of arterial pressure. Investigation into sex differences in the developmental programming of hypertension may provide critical insight into the mechanisms linking sex hormones and factors important in blood pressure regulation. Understanding the complexity of the developmental programming of adult disease may lead to preventive measures and early detection of cardiovascular risk.

Intrauterine growth restriction: fetal programming of hypertension and kidney disease

The etiology of hypertension historically includes 2 components: genetics and lifestyle. However, recent epidemiologic studies report an inverse relationship between birth weight and hypertension suggesting that a suboptimal fetal environment may also contribute to increased disease in later life. Experimental studies support this observation and indicate that cardiovascular/kidney disease originates in response to fetal adaptations to adverse conditions during prenatal life.

Role of fetal programming in the development of hypertension

Epidemiological studies have suggested that size at birth contributes to increased cardiovascular disease (CVD) risk in later life. Findings from experimental studies are providing insight into the mechanisms linking impaired fetal growth and the increased risk of CVD and hypertension in adulthood. This article summarizes potential mechanisms involved in the fetal programming of hypertension and CVD, including alterations in the organs and regulatory systems critical to long-term control of sodium and volume homeostasis.

Sex differences in the fetal programming of hypertension

BACKGROUND

Numerous clinical and experimental studies support the hypothesis that the intrauterine environment is an important determinant of cardiovascular disease and hypertension.

OBJECTIVE

This review examined the mechanisms linking an adverse fetal environment and increased risk for chronic disease in adulthood with an emphasis on gender differences and the role of sex hormones in mediating sexual dimorphism in response to a suboptimal fetal environment.

METHODS

This review focuses on current findings from the PubMed database regarding animal models of fetal programming of hypertension, sex differences in phenotypic outcomes, and potential mechanisms in offspring of mothers exposed to an adverse insult during gestation. For the years 1988 to 2007, the database was searched using the following terms: fetal programming, intrauterine growth restriction, low birth weight, sex differences, estradiol, testosterone, high blood pressure, and hypertension.

RESULTS

The mechanisms involved in the fetal programming of adult disease are multifactorial and include alterations in the regulatory systems affecting the long-tterm control of arterial pressure. Sex differences have been observed in animal models of fetal programming, and recent studies suggest that sex hormones may modulate activity of regulatory systems, leading to a lower incidence of hypertension and vascular dysfunction in females compared with males.

CONCLUSIONS

Animal models of fetal programming provide critical support for the inverse relationship between birth weight and blood pressure. Experimental models demonstrate that sex differences are observed in the pathophysiologic response to an adverse fetal environment. A role for sex hormone involvement is strongly suggested,with modulation of the renin-angiotensin system as a possible mechanism.

Early renal denervation prevents development of hypertension in growth-restricted offspring

1. Low birth weight is associated with an increased risk for the development of hypertension. Our laboratory uses a model of reduced uterine perfusion in the pregnant rat that results in intrauterine growth-restricted (IUGR) offspring that develop hypertension at a prepubertal age. Although hypertension develops in both prepubertal male and female IUGR offspring, only male IUGR offspring remain hypertensive after puberty. We reported previously that bilateral renal denervation abolishes hypertension in adult male IUGR offspring, indicating an important role for the renal nerves in the maintenance of established IUGR-induced hypertension. We also reported that angiotensin-converting enzyme inhibition abolishes hypertension in adult male IUGR offspring. However, activation of the renin-angiotensin system does not occur in male IUGR offspring until after puberty, or after the development of established IUGR-induced hypertension. Therefore, the mechanisms involved in the development of IUGR-induced hypertension may differ from those involved in the maintenance of established IUGR-induced hypertension. Thus, the purpose of the present study was to determine whether the renal nerves play a causative role in the early development of IUGR-induced hypertension in prepubertal IUGR offspring. 2. Intrauterine growth-restricted and control offspring were subjected to either bilateral renal denervation or sham denervation, respectively, at 4 weeks of age. Mean arterial pressure (MAP) was determined at 6 weeks of age in conscious, chronically instrumented animals. Adequacy of renal denervation was verified by renal noradrenaline content. 3. Whereas renal denervation had no effect on MAP in control offspring (103 +/- 2 vs 102 +/- 3 mmHg for sham vs denervated, respectively), it reduced blood pressure in growth-restricted offspring (114 +/- 3 vs 104 +/- 1 mmHg for sham vs denervated, respectively; P < 0.01). Renal noradrenaline content was significantly reduced in denervated animals relative to sham operated rats. 4. Thus, the data indicate a role for the renal nerves in the aetiology of IUGR-induced hypertension and suggest that the renal nerves may participate in the early development of hypertension in IUGR offspring in addition to established hypertension observed in adult male IUGR offspring.

Estrogen protects against increased blood pressure in postpubertal female growth restricted offspring

Placental insufficiency in the rat results in intrauterine growth restriction and development of hypertension in prepubertal male and female growth-restricted offspring. However, after puberty, only male growth-restricted offspring remain hypertensive, whereas female growth-restricted offspring stabilize their blood pressure to levels comparable to adult female controls. Because female rats reach their maximum levels of estrogen at puberty, we hypothesize that estrogen may be a factor involved in the stabilization of blood pressure in adult female growth-restricted offspring. At 10 weeks of age, female control and growth-restricted offspring underwent ovariectomy or sham surgery and insertion of a telemetry probe. Mean arterial pressure was similar at 16 weeks of age between control (123+/-4 mm Hg) and growth-restricted offspring (122+/-2 mm Hg); however, ovariectomy led to a significant increase in blood pressure in growth-restricted offspring (140+/-2 mm Hg; P<0.05 versus intact counterpart) with no significant effect in controls (124+/-1 mm Hg). Estrogen replacement by subcutaneous minipellet initiated at 14 weeks of age in a subset of ovariectomized control and growth-restricted offspring reversed the effect of ovariectomy on blood pressure in growth-restricted offspring at 16 weeks of age (111+/-3 mm Hg; P<0.05 versus ovariectomized counterpart); renin angiotensin system blockade also abolished ovariectomy-induced hypertension in female growth-restricted offspring (106+/-2 mm Hg; P<0.05 versus ovariectomized counterpart). Therefore, sex differences are observed in this model of fetal programmed hypertension, and results from this study suggest that estrogen contributes to normalization of blood pressure in adult female growth-restricted offspring.