The Relationship of Low Birth Weight to Blood Pressure, Cortisol Levels, and Reactivity in African American Adolescents: A Pilot Study

Blood pressure and the capacity-load model in 8-year-old children from Nepal: Testing the contributions of kidney size and intergenerational effects

Objectives

Growth patterns in early life are increasingly linked with subsequent cardio-metabolic risk, but the underlying mechanisms require elucidation. We have developed a theoretical model of blood pressure, treating it as a function of homeostatic metabolic capacity, and antagonistic metabolic load. We sought to differentiate prenatal and postnatal components of metabolic capacity, and to identify intergenerational contributions to offspring capacity and load.

Methods

We followed up at 8 years a cohort of children originally recruited into a randomized trial of maternal micronutrient supplementation in pregnancy. Maternal anthropometry was measured at recruitment. Offspring anthropometry was measured at birth, 2 years and 8 years. Offspring blood pressure, kidney size, and body composition were measured at 8 years. Regression analysis was used to investigate potential associations of maternal phenotype, birth phenotype, and current body composition with kidney size and blood pressure.

Results

Blood pressure was positively associated with body fat, but negatively associated with birth weight and relative leg length. Kidney size was positively associated with birth weight but not with relative leg length. Adjusting for adiposity, blood pressure was independently negatively associated with birth weight, relative leg length, and kidney length. Maternal height and BMI predicted offspring size at birth and at 8 years, but not blood pressure.

Conclusions

Our data provide support for the capacity-load model of blood pressure in Nepalese children. Fetal and postnatal growth and kidney dimensions all contribute to metabolic capacity. Maternal phenotype contributed to offspring capacity and load, but these associations did not propagate to blood pressure.

Vasomotor sympathetic outflow in the muscle metaboreflex in low birth weight young adults

A growing body of evidence suggests that low birth weight (LBW) offspring are associated with long-term structural and functional changes in cardiovascular and neuroendocrine systems. We tested the hypothesis that muscle metaboreflex activation produces exaggerated responses in cardiac autonomic tone (represented by heart rate variability ratio) and cutaneous vascular sympathetic tone (represented by plethysmography pulse wave amplitude) in LBW compared to normal birth weight (NBW) young adults. We recruited 23 LBW (18 females and five males) and 23 NBW (14 females and nine males) University of Zimbabwe students with neonatal clinical cards as proof of birth weight at term. Resting electrocardiogram, pulse waves, and blood pressures were recorded. Participants then underwent a static/isometric handgrip exercise until fatigue and a post-exercise circulatory arrest period of 2 minutes. We observed (results mean ± standard deviation) a greater mean increase in heart rate variability ratio from baseline to exercise for LBW compared to NBW individuals (1.015±1.034 versus [vs] 0.119±0.789, respectively; P<0.05). We also observed a greater mean decrease in plethysmography pulse wave amplitude from baseline to exercise (−1.32±1.064 vs −0.735±0.63; P<0.05) and from baseline to post-exercise circulatory arrest (−0.932±0.998 vs −0.389±0.563; P<0.05) for LBW compared to NBW individuals. We conclude that LBW may be associated with an exaggerated sympathetic discharge in response to muscle metaboreflex.

The association of hypothalamic-pituitary-adrenal axis activity and blood pressure in an Afro-Caribbean population

Hyperactivity of the hypothalamic-pituitary-adrenal axis (HPAA) resulting from fetal programming may play a role in the development of high blood pressure (BP) in black people. We assessed the diurnal salivary cortisol profile in children with and without increased BP and evaluated their mother's HPAA. In a cross-sectional study, 20 Afro-Caribbean children (mean age 9.6 years) with higher blood pressures and 20 children with lower blood pressures were chosen from a prospective study of 569 mothers and children in Jamaica. Daytime salivary cortisol profiles were collected in the children and their mothers. The mothers were also assessed for features of the metabolic syndrome. Children with higher BP had higher mean morning salivary cortisol concentrations than those with lower BP (7.9 S.D. 1.9 vs. 4.5 S.D. 2.4nmol/l; p=0.03). Their mothers also had increased morning salivary cortisol concentrations (9.9 S.D. 1.8 vs. 5.5 S.D. 2.5nmol/l; p=0.02), but no changes in fasting glucose, insulin, lipids, BP or adiposity. Maternal and offspring cortisol concentrations correlated significantly (r=0.465, p=0.004). Maternal cortisol concentrations were significantly associated with the child's BP. We conclude that Afro-Caribbean children with higher BP have higher morning salivary cortisol concentrations. The children's cortisol concentrations correlate significantly with the mother's cortisol concentrations. These findings suggest that the HPAA may play a role in the development of raised BP in Afro-Caribbean people.

The association of low birth weight and physiological risk factors of hypertension in African American adolescents

Low birth weight (LBW) has been associated with increased blood pressure and the development of cardiovascular disease including hypertension. Elevated blood pressure, cortisol, and hyperresponsiveness during physiologic stress may function as hypertension biological markers. We examined the association of blood pressure and cortisol levels during induced physiologic stress with LBW in an African American adolescent population (n = 106).

METHODS AND RESULTS

Birth weight was obtained from parents. Blood pressure and cortisol levels were measured at rest and in response to an induced physiological stressor. Compared with normal birth weight group (n = 73), the LBW group (n = 33) demonstrated elevated (+4 mm Hg) diastolic pressure (P = .002) and cortisol hyperresponsiveness (P = .05). Seventy-nine percent of LBW adolescents had elevated blood pressure and/or cardiovascular reactivity (P = .04), and 39% had elevated blood pressures.

CONCLUSIONS

Low birth weight African American adolescents demonstrated physiological risk factors for hypertension, and these findings add support to the association between LBW and the development of hypertension.