Impaired acetylcholine-induced vascular relaxation in low birth weight infants: implications for adult hypertension?

Early changes in the biophysical properties of the aorta in pre-adolescent children born small for gestational age

OBJECTIVE

To assess the biophysical properties of the aorta in children born small for gestational age (SGA) with an echo-Doppler method and to determine associations with known perinatal risk factors.

STUDY DESIGN

In this cross-sectional study, 39 SGA and 41 control subjects aged 8 to 13 years were recruited. Perinatal risk factors were recorded. The aortic diameters and pulse wave transit time around the aortic arch were measured with echo-Doppler and the blood pressure recorded. Pulse wave velocity, aortic input impedance (Zi), characteristic impedance (Zc), arterial pressure-strain elastic modulus (Ep), and arterial wall stiffness index (beta-index) were calculated.

RESULTS

Pulse wave velocity (374 +/- 46 vs 348 +/- 47 cm/sec, P < .02); Zi (177 +/- 39 vs 142 +/- 27 dynes x sec/cm(5), P < .0001); Zc (185 +/- 29 vs 152 +/- 37 dynes x sec/cm(5), P < .0001); Ep (286 +/- 101 vs 216 +/- 41 mm Hg, P < .0001); and beta-index (2.43 +/- 0.32 vs 2.17 +/- 0.15, P < .0001) were all higher in SGA. We found negative associations between the following: birth weight and Zi, Zc, Ep, and beta-index; as well as body mass index and Zi, Zc.

CONCLUSION

This simple echo-Doppler method demonstrated abnormal biophysical properties of the aorta in a cohort of pre-adolescent patients born SGA who remain small in stature and continue to have normal blood pressure.

The relation of arterial stiffness with intrauterine growth retardation

BACKGROUND

Much epidemiological evidence has linked low birthweight with late cardiovascular risk. Intrauterine growth retardation (IUGR) is associated with the increased risk of cardiovascular disease in adult life; it is unclear whether the relationship is present at younger ages. We evaluated whether abdominal aortic stiffness was altered in patients with IUGR (born at term with birthweight small for gestational age) in younger ages.

METHODS

Thirty-two (24 girls and eight boys) IUGR children aged 8.77 +/- 2.05 years were enrolled in the study. The birthweight was traced from the medical records. Their gestational ages were 38.9 +/- 0.85 weeks and birthweights 2130 +/- 198 g, respectively. Thirty-one healthy subjects who had normal gestational age and birthweight, matched for age and sex were recruited as a control group. Aortic strain, pressure strain elastic modulus (Ep), and normalized Ep and aortic distensibility were measured by a sphygmomanometer and transthoracic echocardiography in all subjects from the abdominal aorta.

RESULTS

There was no statistically significant difference between the study and the control groups in sex, mean age, body mass index, lipid profile, leptin, insulin-like growth factor-1 or insulin-like growth factor binding protein 3. In IUGR children, aortic strain (0.201 +/- 0.027 vs 0.254 +/- 0.031, P < 0.001) and aortic distensibility (1.08 +/- 0.19 vs 1.42 +/- 0.24, P < 0.001) were significantly lower compared with the control group. However Ep (188 +/- 36.2 vs 146 +/- 27.1, P < 0.001) and normalized Ep (2.97 +/- 0.40 vs 2.1 +/- 0.39, P < 0.001) were significantly higher in IUGR patients.

CONCLUSIONS

This study demonstrates that abdominal aortic stiffness is increased in IUGR patients. These data suggest that prenatal events could be related to cardiovascular risk in later life.

The implications of fetal programming of glomerular number and renal function

Large epidemiological studies suggest a clear relation between low birth weight and adverse renal outcomes evident as early as during childhood. Such adverse outcomes may include glomerular disease, hypertension, and renal failure. Data from autopsy material and from experimental models suggest that reduction in nephron number via diminished nephrogenesis may be a major mechanism, and factors that lead to this reduction are incompletely elucidated. Other mechanisms appear to be renal (e.g., via the intrarenal renin-angiotensin-aldosterone system) and nonrenal (e.g. changes in endothelial function). It also appears likely that the outcomes of fetal programming may be influenced postnatally, for example, by the amount of nutrients given at critical times.

No evidence for an enhanced role of endothelial nitric oxide in the maintenance of arterial blood pressure in the IUGR sheep fetus

The fetus makes a number of physiological adaptations to a restriction of placental substrate supply, including a decrease in body growth and an increase in peripheral vasoconstriction which maintains mean arterial pressure (MAP) and supports a redistribution of cardiac output to key fetal organs. It is not known, however, whether chronic restriction of placental substrate supply results in an enhanced or diminished role for vasodilators such as endothelial nitric oxide in the regulation of MAP. We hypothesised that there is an increased contribution of NO to blood pressure regulation in growth restricted fetuses and that a 2h infusion of a nitric oxide synthase inhibitor, N(omega)-nitro-l-arginine methyl ester (l-NAME) would result in an augmented rise in MAP in chronically hypoxemic, placentally restricted (PR, n=8) fetuses compared to controls (n=6) in late gestation. There was no difference in the increase in fetal MAP and decrease in HR during l-NAME infusion between Control and PR fetuses. In the PR group, fetuses with lower mean gestational PaO(2) had a lower increase in MAP during l-NAME infusion. Thus we have found no evidence for an enhanced role of NO in the maintenance of MAP in the chronically hypoxemic IUGR fetus.

Low birth weight and the developing vascular tree: a systematic review

Low birth weight (LBW) is a risk factor for hypertension, stroke and coronary heart disease in adults. Mechanisms underlying cardiovascular disease may therefore be initiated in early life. Studies to investigate the initiating events and emergence of vascular risk markers in infancy and childhood have been an area of particular interest in recent years. The aim of this review is to focus on the early development of the human vascular tree in relation to LBW. Specific characteristics, including endothelial function, intima-media thickness, microvascular density, arterial dimensions and elasticity, will be discussed. LBW due to different causes--poor foetal growth or preterm birth--results in different patterns of altered development of the vascular system, which can already be seen in infancy. Follow-up studies in children and young adults indicate that vascular compromise in many ways persists in those born either small for gestational age or prematurely.

CONCLUSION

LBW is associated with structural and functional changes in the vascular tree, which have implications for cardiovascular health in adult life.

Endothelial function in children with a history of premature prolonged rupture of membranes and bronchopulmonary dysplasia--a pilot study

AIM

To investigate vascular function in children with a neonatal history of generalised inflammation indicated by premature prolonged rupture of membranes (PPROM) and bronchopulmonary dysplasia (BPD).

METHODS

Children born at <or=30 weeks 1994-2000 were investigated at a present age of 6-12 years. Twenty-eight children participated and were divided into two groups with regard to BPD/no BPD (n=15/13) and PPROM/no PPROM (n=10/18). Vascular endothelial function was assessed by acetylcholine (ACh)-induced skin vasodilatation.

RESULTS

Maximum ACh-induced skin perfusion was statistically significantly lower in the PPROM group compared with the non-PPROM group (p=0.045) after adjustment for confounders. We found no association between BPD and maximum ACh-induced skin perfusion (p=0.404), after adjustment for confounders.

CONCLUSION

A neonatal history of prolonged premature rupture of membranes was associated with later impairment of vascular endothelial function in childhood. This association was not observed with BPD. Some forms of perinatal inflammation may be associated with later cardiovascular function.

Sex-specific differences in peripheral microvascular blood flow in preterm infants

Microvascular blood flow is related to physiologic instability in newborn preterm infants. We investigated sex-specific differences in basal microvascular blood flow and the ability of the microvasculature to respond to vasoactive stimuli following preterm birth. Ninety-six infants in two gestational age groups (24-28 and 29-36 wk) were studied on days 1-5 of life. Laser Doppler flowmetry was used to measure baseline microvascular blood flow and vasodilatation in response to acetylcholine and local warming. A significant interaction of gestational age and sex was observed for baseline flow at 24 h of age. In the 24-28 wk group, male infants had higher baseline flow than females. Male, but not female, infants born at 24-28 wk exhibited a significant relationship between baseline flow and vasodilatory response to acetylcholine at 24 h of age. By 120 h of age, both sexes exhibited similar responses. Infants born at 24-28 wk exhibited greater vasodilatation in response to local warming than those born at 29-36 wk at 24, 72, and 120 h of age. Sex-specific differences in microvascular blood flow and vasodilatory capacity in the immediate newborn period may affect the transitional circulation, contributing to excess of morbidity and mortality in preterm males.

Mechanisms underlying developmental programming of elevated blood pressure and vascular dysfunction: evidence from human studies and experimental animal models

Cardiovascular-related diseases are the leading cause of death in the world in both men and women. In addition to the environmental and genetic factors, early life conditions are now also considered important contributing elements to these pathologies. The concept of 'fetal' or 'developmental' origins of adult diseases has received increased recognition over the last decade, yet the mechanism by which altered perinatal environment can lead to dysfunction mostly apparent in the adult are incompletely understood. This review will focus on the mechanisms and pathways that epidemiological studies and experimental models have revealed underlying the adult cardiovascular phenotype dictated by the perinatal experience, as well as the probable key causal or triggering elements. Programmed elevated blood pressure in the adult human or animal is characterized by vascular dysfunction and microvascular rarefaction. Developmental mechanisms that have been more extensively studied include glucocorticoid exposure, the role of the kidneys and the renin-angiotensin system. Other pathophysiological pathways have been explored, such as the role of the brain and the sympathetic nervous system, oxidative stress and epigenetic changes. As with many complex diseases, a unifying hypothesis linking the perinatal environment to elevated blood pressure and vascular dysfunction in later life cannot be presumed, and a better understanding of those mechanisms is critical before clinical trials of preventive or 'deprogramming' measures can be designed.

Microcirculation in obesity: an unexplored domain

Obesity is traditionally linked to diabetes and cardiovascular diseases. Very recent experimental, clinical and epidemiological, sometimes provocative, data challenge this automaticity by showing that not the amount but the distribution of fat is the important determinant. Moderate abdominal fat accumulation may thus be more harmful than even consequent overweight. In view of the worldwide burden of obesity, factors leading to it in children and young adults must urgently be identified. Since obesity is a very complex cardiometabolic situation, this will require to focus investigations on uncomplicated obese subjects and adequate animal models. The recent discovery of intergenerational transmissions of obesity risk factors and also the key role played by gestational and perinatal events (epigenetic factors) give rise to completely new concepts and research avenues. Considering the potential close relationship between microcirculation and tissue metabolism, demonstrations of structural and/or functional abnormalities in microvascular physiology very early in life of subjects at risk for obesity might provide a solid basis for further investigations of such links. Microcirculation(arterioles, capillaries and venules) is conceivably a key compartment determining over one or several decades the translation of genetic and epigenetic factors into fat accumulation. Available animal models should serve to answer this cardinal question.

Fetal growth restriction in preterm infants and cardiovascular function at five years of age

OBJECTIVES

We have previously reported an increased cardiac workload in newborn preterm small (SGA) infants, but not in infants appropriate for gestational age (AGA). We hypothesized that these cardiovascular changes will persist at follow-up at 5 years of age.

STUDY DESIGN

We assessed blood pressure, echocardiography, and skin perfusion with laser Doppler flowmetry in 22 SGA (821 +/- 248 g, 28.5 +/- 2.5 gestational weeks) and in 25 AGA (1065 +/- 241 g, 27.6 +/- 0.8 weeks) preterm children at age 5 years. Laser Doppler flowmetry also was used in 13 control children (3982 +/- 425 g, 40.4 +/- 1.8 weeks).

RESULTS

The preterm children in both the SGA and AGA groups had similar higher systolic blood pressures, increased interventricular septum thicknesses, and smaller left ventricular end-diastolic diameters compared with population reference values. Maximal endothelium-independent perfusion to sodium nitroprusside was higher and maximal endothelium-dependent perfusion to acetylcholine reached a plateau earlier in the AGA preterm group than in the control group.

CONCLUSIONS

Prematurity may impair cardiovascular function independently of intrauterine growth restriction. Altered cardiac dimensions and differences in perfusion responses may reflect increased cardiac afterload.

Endothelial function in newborn infants is related to folate levels and birth weight

OBJECTIVE

Low maternal folate levels during pregnancy correlate with low birth weight, a perinatal risk factor for later cardiovascular disease. We studied relationships between red blood cell folate levels, birth weight, and vascular endothelial function (a key factor in the early pathophysiologic processes of heart disease) in newborn infants.

METHODS

We included 82 infants (30 low birth weight) and their mothers. A laser Doppler technique was used to measure skin perfusion during transdermal iontophoresis of acetylcholine (an endothelium-dependent vasodilator). Red blood cell folate, vitamin B12, and homocysteine levels were determined.

RESULTS

The perfusion response to acetylcholine was lower in low birth weight infants than in normal birth weight control subjects (mean: 35 vs 76 perfusion units). The neonatal acetylcholine response correlated with red blood cell folate levels in both infants and their mothers. The folate levels of low birth weight and control infants did not differ significantly (mean: 1603 vs 1795 nmol/L), but mothers of low birth weight infants had lower folate levels than did mothers of control infants (mean: 805 vs 1109 nmol/L). In multivariate analysis, low birth weight and red blood cell folate levels contributed independently to endothelial function in newborn infants. The levels of vitamin B12 and homocysteine were similar in the 2 groups and did not correlate with endothelial function.

CONCLUSION

The data presented here provide the first evidence for a relationship between folate levels and vascular endothelial function in newborn infants.

Intrauterine growth restriction delays cardiomyocyte maturation and alters coronary artery function in the fetal sheep

There is now extensive evidence suggesting that intrauterine perturbations are linked with an increased risk of developing cardiovascular disease. Human epidemiological studies, supported by animal models, have demonstrated an association between low birth weight, a marker of intrauterine growth restriction (IUGR), and adult cardiovascular disease. However, little is known of the early influence of IUGR on the fetal heart and vessels. The aim of this study was to determine the effects of late gestational IUGR on coronary artery function and cardiomyocyte maturation in the fetus. IUGR was induced by placental embolization in fetal sheep from 110 to 130 days of pregnancy (D110-130); term approximately D147; control fetuses received saline. At necropsy (D130), wire and pressure myography was used to test endothelial and smooth muscle function, and passive mechanical wall properties, respectively, in small branches of left descending coronary arteries. Myocardium was dissociated for histological analysis of cardiomyocytes. At D130, IUGR fetuses (2.7 +/- 0.1 kg) were 28% lighter than controls (3.7 +/- 0.3 kg; P = 0.02). Coronary arteries from IUGR fetuses had enhanced responsiveness to the vasoconstrictors, angiotensin II and the thromboxane analogue U46619, than controls (P < 0.01). Endothelium-dependent and -independent relaxations were not different between groups. Coronary arteries of IUGR fetuses were more compliant (P = 0.02) than those of controls. The incidence of cardiomyocyte binucleation was lower in the left ventricles of IUGR fetuses (P = 0.02), suggestive of retarded cardiomyocyte maturation. We conclude that late gestational IUGR alters the reactivity and mechanical wall properties of coronary arteries and cardiomyocyte maturation in fetal sheep, which could have lifelong implications for cardiovascular function.

Reduced intima media thickness in adults after prenatal exposure to the Dutch famine

BACKGROUND

Restricted prenatal growth is associated with an increased risk of coronary heart disease morbidity and mortality. We studied the effects of exposure to famine during gestation on intima media thickness (IMT) in later life.

METHODS AND RESULTS

We studied 730 people aged 58 years who were born as term singletons around the time of the 1944-45 Dutch famine. Persons exposed to famine during gestation (n=293) had reduced carotid artery IMT compared to people who had not been exposed to famine in utero (n=437) (mean 0.71 mm, S.D. 0.16 mm compared to 0.75 mm, S.D. 0.15 mm, sex adjusted p=0.001). Femoral artery IMT was also thinner among people exposed to famine during gestation compared to people unexposed in utero (mean 0.64 mm, S.D. 0.20mm, compared to 0.68 mm, S.D. 0.24), although the difference did not achieve statistical significance.

CONCLUSION

Exposure to famine in utero may reduce IMT. However, it does not reduce the risk of coronary heart disease among famine exposed people.

Early gestation dexamethasone alters baroreflex and vascular responses in newborn lambs before hypertension

Exposure of the early gestation ovine fetus to exogenous glucocorticoids induces alterations in postnatal cardiovascular physiology, including hypertension. To determine whether autonomic function and systemic vascular reactivity are altered by in utero programming before the development of systemic hypertension, we examined arterial baroreflex function and in vivo hemodynamic and in vitro vascular responses to vasoactive agents in 10- to 14-day-old newborn lambs exposed to early gestation glucocorticoids. Dexamethasone (Dex, 0.28 mg·kg−1·day−1) or saline was administered to pregnant ewes by intravenous infusion over 48 h beginning at 27 days gestation (term 145 days), and lambs were allowed to deliver ( n = 6 in each group). Resting mean arterial blood pressure (MABP; 77 ± 1 vs. 74 ± 3 mmHg) and heart rate (HR; 249 ± 9 vs. 226 ± 21 beats/min) were similar in Dex-exposed and control animals, respectively. The arterial baroreflex curve, relating changes in HR to MABP, was significantly shifted toward higher pressure in the Dex-exposed lambs although no change in the sensitivity (gain) of the response was seen. In vivo changes in blood pressure in response to bolus doses of ANG II (20, 50, and 100 ng/kg) and phenylephrine (2, 5, and 10 μg/kg) were similar in the two groups. However, Dex lambs displayed greater decreases in MABP in response to ganglionic blockade with tetraethylammonium bromide (10 mg/kg; −30 ± 3 vs. −20 ± 3 mmHg, P < 0.05) and greater increases in MABP after nitric oxide synthase blockade with NG-nitro-l-arginine (25 mg/kg; 23 ± 3 vs. 13 ± 2 mmHg, P < 0.05) compared with control lambs. By in vitro wire myography, mesenteric and femoral artery microvessel contractile responses to KCl were similar, whereas responses to endothelin (in mesenteric) and norepinephrine (in femoral) were significantly attenuated in Dex lambs compared with controls. Femoral vasodilatory responses to forskolin and sodium nitroprusside were similar in the two groups ( n = 4). These findings suggest that resetting of the baroreflex, accompanied by increased sympathetic activity and altered nitric oxide-mediated compensatory vasodilatory function, may be important contributors to programming of hypertension.

Folate, vitamin B12, and homocysteine levels in South Asian women with growth-retarded fetuses

OBJECTIVE

To investigate whether intrauterine growth retardation (IUGR) and preterm delivery in a poor population of South Asia was associated with altered maternal and fetal levels of folate, vitamin B12, and homocysteine.

SUBJECTS AND METHODS

Hundred and twenty-eight pregnant women from a low socio-economic strata in the city of Lahore, Pakistan were followed with ultrasound of fetal growth from the 12th week of pregnancy. Blood samples were drawn from the woman and the cord at delivery. Serum was analyzed by a chemiluminescent immunoassay for folate and vitamin B12 and by fluorescence polarization immunoassay for total homocysteine (tHcy).

RESULTS

Fourty-six infants showed IUGR. In term, but not preterm, deliveries with IUGR, maternal and cord blood folate levels were half of those in deliveries of normal birth weight infants (P=0.004 and P=0.005). The risk of IUGR was reduced among women with folate levels in the highest quartile (OR 0.31, 95% CI 0.10--0.84). There was no association between vitamin B12 and IUGR. Total homocysteine levels were higher in women delivering IUGR infants (P=0.02). There was an inverse correlation between cord blood folate and tHcy levels (r=-0.26, P=0.006). We also found increased risks for hypertensive illness (OR 3.5, 95% CI 1.4--8.6) and premature delivery (OR 2.5, 95% CI 1.1--6.2) in women in the highest quartile of tHcy.

CONCLUSIONS

The occurrence of IUGR increased with low maternal and cord concentrations of folate and high maternal levels of tHcy. Further studies on the effects of vitamin B supplementation through pregnancy are warranted.

Preterm birth contributes to increased vascular resistance and higher blood pressure in adolescent girls

Preterm birth might induce permanent changes in vascular structure and function as well as in blood pressure. To elucidate this hypothesis and underlying mechanisms in girls born before term, the authors correlated neonatal data, including estradiol levels, with vascular function and structure and with blood pressure after puberty. In a case-control study design, 34 girls born before term and 32 gender- and age-matched control infants born at term were included. Pulse wave analysis was used to determine aortic pressure profiles and overall arterial compliance. Stiffness of the carotid artery and abdominal aorta was measured with ultrasonography. Pulse wave velocity in the forearm was measured with photoplethysmography. A laser Doppler technique was used to determine skin perfusion before and after transdermal delivery of acetylcholine, an endothelium-dependent vasodilator. It was found that preterm girls had significantly higher brachial and aortic blood pressure, a narrower but less stiff abdominal aorta, and lower peripheral skin blood flow than did control infants. Augmentation index, carotid stiffness, pulse wave velocity, endothelium-dependent vasodilatation, and heart rate were similar in the two groups. In the preterm group, blood pressure and vascular functions showed no association with intrauterine growth retardation or neonatal estradiol levels. In conclusion, preterm girls have higher blood pressure and an increased resistance in the vascular tree after puberty. These findings may have implications for future cardiovascular risk in the growing adult population surviving preterm birth.

The prenatal environment and later cardiovascular disease

Exposure of an embryo or fetus to a sub-optimal environment increases its risk of acquiring coronary disease and heart failure in adult life through a process known as programming. For example, stress experienced in utero and during early postnatal life imparts an increased vulnerability for adult onset cardiovascular disease. Programming is a change in gene expression pattern that occurs in response to a stressor and leads to altered growth of specific organs during their most critical times of development. Known stressors include improper nourishment, hypoxia and excess glucocorticoids. Programming becomes evident through a number of risk factors that are only now becoming understood, including growth patterns in childhood, structural and cellular changes to the heart and coronary vessels, impaired endothelial function, and altered lipid metabolism. Thus, adults most vulnerable for coronary artery disease may have experienced rapid weight gain in childhood and now have dyslipidemias and depressed endothelial function.

Effects of maternal hypoxia or nutrient restriction during pregnancy on endothelial function in adult male rat offspring

Compromised fetal growth impairs vascular function; however, it is unclear whether chronic hypoxia in utero affects adult endothelial function. We hypothesized that maternal hypoxia (H, 12% O2, n= 9) or nutrient restriction (NR, 40% of control, n= 7) imposed from day 15-21 pregnancy in rats would impair endothelial function in adult male offspring (relative to control, C, n= 10). Using a wire myograph, endothelium-dependent relaxation in response to methacholine was assessed in small mesenteric arteries from 4- and 7-month-old (mo) male offspring. Nitric oxide (NO) mediation of endothelium-dependent relaxation was evaluated using N(omega)-nitro-L-arginine methyl ester (L-NAME; NO synthase inhibitor). Observed differences in the NO pathway at 7 months were investigated using exogenous superoxide dismutase (SOD) to reduce NO scavenging, and sodium nitroprusside (SNP; NO donor) to assess smooth muscle sensitivity to NO. Sensitivity to methacholine-induced endothelium-dependent relaxation was reduced in H offspring at 4 months (P < 0.05), but was not different among groups at 7 months. L-NAME reduced methacholine sensitivity in C (P < 0.01), H (P < 0.01) and NR (P < 0.05) offspring at 4 months, but at 7 months L-NAME reduced sensitivity in C (P < 0.05), tended to in NR (P= 0.055) but had no effect in H offspring. SOD did not alter sensitivity to methacholine in C, but increased sensitivity in H offspring (P < 0.01). SNP responses did not differ among groups. In summary, prenatal hypoxia, but not nutrient restriction impaired endothelium-dependent relaxation at 4 months, and reduced NO mediation of endothelial function at 7 months, in part through reduced NO bio-availability. Distinct effects following reduced maternal oxygen versus nutrition suggest that decreased oxygen supply during fetal life may specifically impact adult vascular function.

Differential effects of maternal hypoxia or nutrient restriction on carotid and femoral vascular function in neonatal rats

In response to reduced oxygen or nutrient supply, the fetus may redistribute cardiac output to conserve brain and heart growth, at the expense of the peripheral tissues; however, it is not known whether alterations in vascular function are maintained after birth or whether reduced fetal oxygen versus nutrient supply produces distinct effects. Using a pressure myograph, we examined isolated carotid and femoral artery responses to phenylephrine and endothelin-1 in neonatal rats, after either reduced maternal oxygen or global nutrient restriction during late gestation. Timed-pregnant Sprague-Dawley rats were randomly assigned to control ( n = 10), hypoxia (12% O2, n = 9), or nutrient restriction (NR, 40% of control diet, n = 7) protocol and treated from day 15–21 of pregnancy. Pups were collected 3–12 h after birth. Neonatal weights ( P < 0.001) and relative liver weights ( P < 0.001) were lower in hypoxia and nutrient restriction treatments compared with control, while relative heart weights were greater in the hypoxia than in the control or nutrient restriction groups ( P < 0.01). Constriction to phenylephrine was reduced in carotid arteries from the hypoxia and nutrient restriction groups compared with control ( P < 0.001), while the femoral artery response was greater in hypoxia-treated neonates compared with control or nutrient-restricted neonates ( P < 0.01). Only the hypoxia reduced carotid responses to endothelin-1, while no differences were observed in the endothelin-1 responses in femoral arteries. Maternal hypoxia and maternal nutrient restriction produced distinct effects on heart growth and neonatal vascular function, suggesting that regional changes in cardiovascular function after poor fetal growth are dependent on the nature of the insult in utero.

Dutch women with a low birth weight have an increased risk of myocardial infarction later in life: a case control study

Background

To investigate whether low birth weight increases the risk of myocardial infarction later in life in women.

Methods

Nationwide population-based case-control study. Patients and controls: 152 patients with a first myocardial infarction before the age of 50 years in the Netherlands. 568 control women who had not had a myocardial infarction stratified for age, calendar year of the index event, and area of residence.

Results

Birth weight in the patient group was significantly lower than in control women (3214 vs. 3370 gram, mean difference -156.3 gram (95%CI -9.5 to -303.1). The odds ratio for myocardial infarction, associated with a birth weight lower than 3000 gram (20^th percentile in controls) compared to higher than 3000 gram was 1.7 (95%CI 1.1–2.7), while the odds ratio for myocardial infarction for children with a low birth weight (< 2000 g) compared to a birth weight ≥ 2000 g was 2.4 (95%CI 1.0 – 5.8). Both figures did not change after adjustment for putative confounders (age, education level, body mass index, waist-hip ratio, hypertension, diabetes, hypercholesterolemia, smoking, and family history of cardiovascular disease).

Conclusions

Low birth weight is associated with an increased risk of myocardial infarction before age of 50 in Dutch women.

Disturbances in Renal Autoregulation and the Susceptibility to Hypertension-Induced Chronic Kidney Disease

The risk of developing chronic kidney disease in the setting of hypertension varies among patient populations. Black hypertensive patients have an increased risk of developing hypertension-induced chronic kidney disease even after taking into account socioeconomic factors. There is evidence to suggest that the kidney is intrinsically more susceptible to the damaging effects of hypertension in black patients. This susceptibility can be traced to disturbances in the way the kidney autoregulates. Impaired renal autoregulation may be the renal manifestation of a more widespread abnormality in endothelial function. Other conditions that can impair renal autoregulation and add to the risk of chronic kidney disease include low birth weight, obesity, insulin resistance, hyperuricemia, and hypercholesterolemia. To minimize the risk of chronic kidney disease in patients with impaired renal autoregulatory capability, strict blood pressure control is required. There is indirect evidence that blocking the renin-angiotensin system may improve renal autoregulation.

Hypertension research in the 21st century

This paper presents a signpost for hypertension research, emphasizing areas most likely to yield major clinical and public health benefits. Specific questions are posed in the context of fetal and maternal precursors of cardiovascular disease, vascular biology, resistant hypertension, antihypertensive drugs, primary aldosteronism, lifestyle and genetic interactions and translational research. Worldwide increasing rates of obesity and diabetes demonstrate the need for a global approach to cardiovascular risk and the need for more effective use of existing knowledge. Equal emphasis is given to the critical importance of the fundamental research required to defeat hypertensive cardiovascular disease in the long run.

Relation of arterial stiffness with gestational age and birth weight

BACKGROUND

The cardiovascular risk of individuals who are born small as a result of prematurity remains controversial. Given the previous findings of stiffer peripheral conduit arteries in growth restricted donor twins in twin-twin transfusion syndrome regardless of gestational age, we hypothesised that among children born preterm, only those with intrauterine growth retardation are predisposed to an increase in cardiovascular risks.

AIM

To compare brachioradial arterial stiffness and systemic blood pressure (BP) among children born preterm and small for gestational age (group 1, n = 15), those born preterm but having birth weight appropriate for gestational age (group 2, n = 36), and those born at term with birth weight appropriate for gestational age (group 3, n = 35).

METHODS

Systemic BP was measured by an automated device (Dinamap), while stiffness of the brachioradial arterial segment was assessed by measuring pulse wave velocity (PWV). The birth weight was adjusted for gestational age and expressed as a z score for analysis.

RESULTS

The 86 children were studied at a mean (SD) age of 8.2 (1.7) years. Subjects from group 1, who were born at 32.3 (2.0) weeks' gestation had a significantly lower z score of birth weight (-2.29 (0.63), p<0.001), compared with those from groups 2 and 3. They had a significantly higher mean blood pressure (p<0.001) and their diastolic blood pressure also tended to be higher (p = 0.07). Likewise, their brachioradial PWV, and hence arterial stiffness, was the highest of the three groups (p<0.001). While subjects from group 2 were similarly born preterm, their PWV was not significantly different from that of group 3 subjects (p = 1.00) and likewise their z score of birth weight did not differ (-0.01 (0.71) v -0.04 (1.1), p = 1.00). Brachioradial PWV correlated significantly with systolic (r = 0.31, p = 0.004), diastolic (r = 0.38, p<0.001), and mean (0.47, p<0.001) BP, and with z score of birth weight (r = -0.43, p<0.001). Multiple linear regression identified mean BP and z score of birth weight as significant determinants of PWV.

CONCLUSION

The findings of the present study support the hypothesis that among children born preterm, only those with intrauterine growth retardation are disadvantaged as a result of increase in systemic arterial stiffness and mean blood pressure.

Abnormal retinal vascular morphology in young adults following intrauterine growth restriction

OBJECTIVE

Intrauterine growth restriction (IUGR) resulting in low birth weight for gestational age may predispose one to development of cardiovascular disease later in life. Abnormal fetal blood flow in the presence of fetal growth restriction helps to distinguish infants with true fetal growth impairment from small but normal infants. Our goal was to investigate associations between IUGR with abnormal fetal blood flow and abnormal retinal vascular morphology at 18 years of age.

METHODS

A prospective study was performed with 21 subjects with IUGR (abnormal fetal aortic blood flow velocity; birth weight small for gestational age; median birth weight deviation from the population mean of -31% [range: -22% to -42%] and in 23 subjects with birth weight appropriate for gestational age [normal fetal aortic blood flow velocity; median birth weight deviation of -2% (range: -10% to 22%)]). The retinal vessel morphology was evaluated by digital image analysis.

RESULT

Subjects with IUGR (n = 21) had significantly less retinal vascularization as evidenced by a lower number of vascular branching points (median: 26; range: 20-31) as compared with the subjects who were born appropriate for gestational age (median: 28; range: 26-32). Within the entire group (N = 44), increasing negative birth weight deviation was associated with a reduced number of vascular branching points (r = 0.36.

CONCLUSION

Our findings show that IUGR with abnormal fetal blood flow is associated with abnormal retinal vascular morphology in young adult life.

Preterm birth attenuates association between low birth weight and endothelial dysfunction

BACKGROUND

Low birth weight predisposes to later coronary disease. To further elucidate the mechanisms behind this association and their timing, vascular endothelial function-a key factor in early pathophysiology of atherosclerosis-was studied in 54 infants born either before the third trimester or at term.

METHODS AND RESULTS

All subjects were studied at 3 months of postnatal age. A laser-Doppler technique was used to measure skin perfusion before and after transdermal iontophoresis of acetylcholine (ACh; an endothelium-dependent vasodilator). In infants born at term (n=19; birth weight range: 2230 to 4205 g), maximum perfusion after ACh was 109+/-8 perfusion units (PU, mean+/-SEM) in normal-birth weight controls compared with 56+/-13 PU among those who had been small for gestational age at birth (P<0.01). In infants born preterm (n=35; birth weight range, 722 to 1868 g), ACh induced similar perfusion responses among subjects appropriate for gestational age (113+/-16 PU) and in those small for gestational age at birth (109+/-19 PU).

CONCLUSIONS

Impairment in human endothelial function associated with low birth weight occurs or emerges late in pregnancy. Very preterm birth attenuates this association. Different gene-environment interactions in the third trimester may contribute to this finding.

Altered vascular function in fetal programming of hypertension

BACKGROUND AND PURPOSE

Reduced endothelium-dependent vasorelaxation partly due to loss of nitric oxide (NO) bioavailability occurs in most cases of chronic hypertension. Intrauterine nutritional deprivation has been associated with increased risk for hypertension and stroke, associated with relaxant dysfunction and decreased vascular compliance, but the underlying mechanisms are not known. The present studies were undertaken to investigate whether endothelial dysfunction associated with altered NO-dependent vasodilatation pathways is also observed in a model of in utero programming of hypertension.

METHODS

Pregnant Wistar rats were fed a normal (18%), low (9%), or very low (6%) protein isocaloric diet during gestation. Vasomotor response of resistance cerebral microvessels (<50 micro m) was studied in adult offspring of dams fed the 18% and 9% protein diets by a video imaging technique. Endothelial NOS (eNOS), soluble guanylate cyclase (sGC), and K(Ca) channel expression were measured by Western blot. NO synthase (NOS) activity was measured enzymatically as well as in situ by NADPH diaphorase staining.

RESULTS

Litter size and survival to adulthood were not affected by the diets. Birth weights of offspring of dams fed the 6% diet were markedly lower than those of dams fed the 9% diet, which were marginally lower than those of controls. Systolic blood pressures of adult offspring of mothers in the 6% and 9% groups were comparably greater (156+/-2 and 155+/-1 mm Hg, respectively) than that of control offspring (137+/-1 mm Hg); we therefore focused on the 9% and 18% groups. Cerebral microvessel constriction to thromboxane A(2) mimetic and dilation to carba-prostaglandin I(2) did not differ between diet groups. In contrast, vasorelaxation to the NO-dependent agents substance P and acetylcholine was diminished by 50% in low protein-exposed offspring, but eNOS expression and activity were similar between the 2 diet groups. Vasorelaxant response to the NO donor sodium nitroprusside was also decreased and was associated with reduced (by 50% to 65%) cGMP levels and sGC expression. cGMP analogues caused comparable vasorelaxation in the 2 groups. Expression of K(Ca) (another important mediator of NO action) and relaxation to the K(Ca) opener NS1619 were unchanged by antenatal diet.

CONCLUSIONS

Maternal protein deprivation, which leads to hypertension in the offspring, is associated with diminished NO-dependent relaxation of major organ (cerebral) microvasculature, which seems to be largely attributed to decreased sGC expression and cGMP levels. The study provides an additional explanation for abnormal vasorelaxation in nutrient-deprived subjects in utero.

The association between birth weight and capillary recruitment is independent of blood pressure and insulin sensitivity: a study in prepubertal children

OBJECTIVE

Alterations in microvascular function have been hypothesized as a possible mechanism explaining the negative association of weight at birth with blood pressure and insulin resistance in adult life. However, these variables are closely associated, so that it has been difficult to establish whether microvascular dysfunction is a cause or a consequence of increased blood pressure or insulin resistance.

DESIGN

Cohort study.

SETTING

VU University Medical Center, Amsterdam, The Netherlands.

SUBJECTS

Twenty-one prepubertal healthy children showing a wide range in birth weight.

MAIN OUTCOME MEASURES

Birth weight data were obtained from hospital records. Blood pressure was measured with an ambulatory 24-h blood pressure monitor, and insulin sensitivity was assessed with the hyperinsulinaemic euglycaemic clamp technique. Microvascular function (i.e. capillary recruitment during post-occlusive reactive hyperaemia and endothelium (in)dependent vasodilatation of the skin) was evaluated by videomicroscopy and iontophoresis of acetylcholine and sodium nitroprusside.

RESULTS

Birth weight was positively and significantly associated with capillary recruitment [slope, 22%/kg birth weight; 95% confidence interval (CI), 0.1-43; 0.05]. Birth weight was not associated with insulin sensitivity and systolic blood pressure (slope, -0.11 mg/kg per min per pmol/l; 95% CI, -2.4 to 2.2; = 0.9; and slope, 1.4 mmHg; 95% CI, -5.0 to 7.7/kg birth weight; = 0.7, respectively). The association between low birth weight and impaired capillary recruitment was not affected by adjustment for blood pressure and insulin sensitivity. Birth weight was not associated with endothelium-(in)dependent vasodilatation.

CONCLUSION

These results suggest that the association between birth weight and capillary recruitment is independent of blood pressure and insulin sensitivity. These findings are consistent with the hypothesis that an impaired capillary recruitment plays a mechanistic role in the association of birth weight with blood pressure and insulin resistance in adult life.

Size at birth and carotid atherosclerosis in later life

Several studies have shown that low birthweight is associated with a higher risk of stroke and coronary heart disease in later life. Increased atherogenesis may be one underlying mechanism, but few studies have examined this directly. We used duplex ultrasonography to assess the extra-cranial carotid arteries of 389 elderly men and women born and still living in Sheffield, UK, whose recorded birth measurements were available. Men and women who had weighed 6.5 lbs or less at birth had a higher risk of having carotid stenosis >30% than those who weighed over 7.5 lbs, but this trend was not statistically significant (OR 1.8, 95% CI 1.0-3.3). Women who had been lighter or who had a smaller head circumference at birth tended to have an increased intima-media thickness, but these relations ceased to be statistically significant after adjustment for gestational age and cardiovascular risk factors. In men, by contrast, an increased intima-media thickness was associated with having been heavier at birth (P=0.049) or having had a larger abdominal circumference at birth (P=0.040), after adjustment for gestational age and cardiovascular risk factors. These results provide little evidence that impaired fetal growth increases susceptibility to atherogenesis.

Birth weight and renal function

Low birth weight due to premature birth or to intrauterine growth retardation adversely affects normal renal development. In the period immediately after birth, the short-term renal-related consequences of low birth weight are an increased risk of acute renal failure as well as transient imbalance of fluid and electrolyte homeostasis. Epidemiological studies show that low birth weight adults are at risk of developing chronic renal disease. There are thought to be several causes for this phenomenon. Adult low birth weight subjects have an increased incidence of hypertension and type 2 diabetes, both of which are well-established risk factors for chronic renal injury. Moreover, interference with normal kidney development, as seen in low birth weight babies, results in a lower than normal number of nephrons, which might also play a role in the renal disturbances.

Fetal origins of adult disease?

1. Associations between lower birthweight and higher blood pressure, increased risk of type 2 diabetes and coronary heart disease (CHD) have been observed in a number of different populations worldwide. 2. The reason for this is still debated. Some believe that the observed associations can be explained on the basis of differences in postnatal growth, socioeconomic confounding or genetic factors. Two published studies of birthweight and CHD, with information on later size, suggest that both gestational and postnatal exposures are important. Associations between birthweight and blood pressure, seen in cohorts of twins treated as individuals, have generally remained when data are analysed within twin pairs. Furthermore, similar associations are seen in studies of animals with relative genetic homogeneity kept in standard conditions. These findings suggest that neither socioeconomic nor genetic factors are wholly responsible for the observed associations. 3. If then, there is an underlying causal association, two issues are of fundamental importance. First, is fetal growth (for which birthweight is a summary measure) involved in the causal pathway or is the causal factor a fetal exposure independently associated with fetal growth and increased risk of adult cardiovascular disease? The answer is important in terms of our understanding, the potential for intervention and estimation of the public health implications. Second, are the classic risk factors for CHD in the causal chain between fetal exposures or growth and adult CHD? Most prospective studies measure these factors, but their role as intermediates is unproven. 4. Intervention studies are the best way to test causal hypotheses, but our level of understanding is insufficient to justify such studies in humans, so we rely on animal studies to formally test causal hypotheses. In the present paper, we discuss design and statistical issues in relation to animal studies. The challenge in this field is to devise ways to identify and test potential causal hypotheses in humans.

Impaired microvascular vasodilatory function in 3-month-old infants of low birth weight

OBJECTIVE

Low birth weight has been linked to an increased risk of type 2 diabetes and cardiovascular disease in adult life. The fetal insulin hypothesis proposed that a genetic predisposition to insulin resistance may also influence vascular development. Therefore, impaired vascular function may be an intrinsic abnormality in low-birth weight infants that antedates clinical features of the insulin resistance syndrome.

RESEARCH DESIGN AND METHODS

Two groups of 3-month-old term infants were included in the study: 17 infants of lowest quartile birth weight (LQBW) and 21 infants of highest quartile birth weight (HQBW). Three aspects of skin microvascular function were examined; response to local heating, response to acetylcholine iontophoresis, and capillary density.

RESULTS

Median (interquartile ranges) birth weights of the LQBW and HQBW infants were 3,140 g (2,738-3,254) and 3,920 g (3,750-4,020), respectively. Skin maximal hyperemic response to local heating was 2.14 V (1.68-2.30) in the LQBW group vs. 2.44 V (1.96-2.90) in the HQBW group (P = 0.020), and the endothelium-dependent vasodilatory response was 1.03 V (0.62-1.32) in the LQBW group vs. 0.78 V (0.45-1.32) in the HQBW group (P = 0.297). Capillary density in the LQBW and HQBW groups were 46.3 mm(-2) (40.1-53.7) and 44.1 mm(-2) (41.7-56.0), respectively (P = 0.736).

CONCLUSIONS

Skin maximal hyperemic response was lower in LQBW infants, although no reduction in capillary density or defect in endothelium-dependent vasodilatation was observed. Such a lower maximal hyperemic response in early life in LQBW subjects who are at risk for type 2 diabetes and cardiovascular disease supports the hypothesis that impaired microvascular function is an early antecedent to diabetes in later life.

Impaired endothelial function and increased carotid stiffness in 9-year-old children with low birthweight

BACKGROUND

Low birthweight (LBW) has been associated with an increased incidence of adult cardiovascular disease. Endothelial dysfunction and loss of arterial elasticity are early markers of hypertension and atherosclerosis. We studied the prevalence of these markers in 44 healthy, prepubertal (age 9+/-1.3 years) children, 22 with LBW for age.

METHODS AND RESULTS

Endothelial function in skin was tested with the local application of acetylcholine (inducing endothelium-dependent vasodilation) and nitroglycerin (endothelium-independent vasodilation), and local perfusion changes were measured with the laser Doppler method. The elastic properties of the abdominal aorta and common carotid artery were measured with an ultrasonic vessel-wall tracking system. Endothelium-dependent vasodilation was lower in children with LBW (88+/-33 perfusion units [PU]) than in normal-birthweight controls (133+/-34 PU, P<0.001). There was no difference in aortic or carotid elasticity between the 2 groups, but a negative correlation was found between birthweight and stiffness of the carotid artery wall (r=-0.45, P<0.01). Endothelium-independent vasodilation and blood pressure were similar in the 2 groups.

CONCLUSIONS

Schoolchildren with a history of LBW show impaired endothelial function and a trend toward increased carotid stiffness. These findings may be early expressions of vascular compromise, contributing to susceptibility to disease in adult life.

Birth weight relates to blood pressure and microvascular function in normal subjects

OBJECTIVE

The relationship between low birth weight and elevated blood pressure in adult life is well established but presently unexplained. Both microvascular dysfunction and insulin resistance have been proposed as a possible explanation. We have examined the relation between birth weight and blood pressure in 30 healthy subjects exhibiting a wide range of insulin sensitivity, and assessed whether microvascular function and/or insulin resistance may underlie this relationship.

METHODS

Birth weight data were obtained from birth announcements. Blood pressure was measured with an ambulatory blood pressure monitor and insulin sensitivity was assessed by the hyperinsulinaemic, euglycaemic clamp technique. Microvascular function, i.e. capillary recruitment and endothelium-dependent and -independent vasodilatation in the skin, was evaluated by videomicroscopy and iontophoresis of acetylcholine and sodium nitroprusside.

RESULTS

Birth weight was significantly associated with blood pressure (r= -0.50; P< 0.05), capillary recruitment (r= +0.52; P< 0.05), acetylcholine-mediated vasodilatation (r= +0.40; P< 0.05), insulin sensitivity (r= +0.62; P< 0.01) and waist-to-hip ratio (r= -0.42; P< 0.05). Regression analysis showed a significant association of birth weight with 24 h systolic blood pressure (regression coefficient: -7.6 mmHg/kg; 95% confidence interval: -13.0 to -1.0). Adjustment for capillary recruitment and waist-to-hip ratio decreased the regression coefficient by 39 and 41%, respectively. The results were similar after adjustment for age, sex or body mass index.

CONCLUSION

These results suggest that capillary recruitment and body fat distribution may partly explain the relationship between birth weight and blood pressure.