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Psychosomatic Medicine 64:906-915 (2002)
© 2002 American Psychosomatic Society

ORIGINAL ARTICLES

Violence Exposure, Catecholamine Excretion, and Blood Pressure Nondipping Status in African American Male Versus Female Adolescents

Dawn K. Wilson, PhD, Wendy Kliewer, PhD, Nicole Teasley, BS, Laura Plybon, PhD and Domenic A. Sica, MD

From the Prevention Research Center and Department of Health Promotion, Education, and Behavior (D.K.W.), Norman J. Arnold School of Public Health, University of South Carolina, Columbia, South Carolina; and the Psychology Department (W.K., L.P.) and Department of Medicine (N.T., D.A.S.), Division of Clinical Pharmacology and Hypertension, Virginia Commonwealth University, Richmond, Virginia.

Address reprint requests to: Dawn K. Wilson, PhD, Prevention Research Center and Department of Health Promotion, Education, and Behavior, Norman J. Arnold School of Public Health, University of South Carolina, 730 Devine Street, Columbia, SC 29208. Email: dkwilson{at}sc.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
OBJECTIVE: Nondipping status (<10% decrease in blood pressure [BP] from awake to asleep) has been associated with end-organ disease (stroke and left ventricular hypertrophy) in adults. Nondipping status has also been observed in 30% of healthy African American adolescents, but little is known about the correlates of nondipping status in adolescents. This study examined the relationship between violence exposure, catecholamine excretion, and BP nondipping status in 56 healthy African American adolescents (27 boys, 29 girls; ages 11–18 years).

METHODS: Participants completed the Survey of Exposure to Community Violence, wore an ambulatory BP monitor and provided one timed day and night urine collection for determination of epinephrine and norepinephrine excretion.

RESULTS: Boys had higher daytime epinephrine (5.1 ± 3.3 vs. 2.6 ± 2.3 ng/min, p < .001) and norepinephrine excretion (29.2 ± 25.1 vs. 16.5 ± 14.9 ng/min, p < .05) and showed a greater prevalence of mean BP nondipping status than girls (37% vs. 10%, p < .03). Mean BP nondipping status was positively associated with victimization (r = 0.42, p < .0001). Regression analyses indicated a significant interaction between hearing about violence and sex for predicting daytime epinephrine (p < .02), with male nondippers showing a stronger positive association (partial correlation = 0.59, p < .05) than females (partial correlation = 0.03, p = NS). Logistic regressions also demonstrated a significant interaction between hearing about violence and sex for predicting mean BP dipping status, with male nondippers reporting the greatest exposure.

CONCLUSIONS: Mean BP nondipping was associated with victimization in both boys and girls. Boys who reported higher levels of hearing about violence showed greater daytime epinephrine excretion and were more likely to be classified as nondippers.

Key Words: ambulatory blood pressure, • catecholamine excretion, • dipping status, • African American adolescents, • violence exposure.

Abbreviations: ABP = ambulatory blood pressure;; BP = blood pressure;; DBP = diastolic blood pressure;; EH = essential hypertension;; MBP = mean blood pressure;; SBP = systolic blood pressure;; SNS = sympathetic nervous system.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
African Americans are at particularly high risk for developing essential hypertension (EH) and cardiovascular disease in early adulthood (1). Furthermore, interracial differences in EH begin in puberty, with African American youth demonstrating higher blood pressure (BP) levels than other ethnic groups (2). Past research on ambulatory blood pressure (ABP) indicates that most people display diurnal variations in BP, with higher pressure during the waking hours and lower pressures during the sleeping hours (3). Although a wide range of definitions have been used to define dipping status, Wilson et al. (4, 5) have reported that approximately 30% of healthy African American adolescents are nondippers across systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean blood pressure (MBP) classifications (show <10% decrease in BP from awake to asleep). Among adults, nondipping status has been associated with a greater prevalence of stroke and left ventricular hypertrophy (6–9). Thus, adolescents who are identified as nondippers may be more likely to develop EH and target organ damage in early adulthood.

Although previous research has indicated a link between environmental factors such as social class and EH (10, 11), little is known about the role of violence exposure on adolescents’ risk for developing EH. Several contextual models have been proposed that suggest that chronic environmental stress may play an important role in the development of hypertension among African Americans. Livingston (12) proposes a sociopsycho-physiological model of the stress process in which external events or demands pose a threat to individuals. Cognitive appraisal of these external events may then lead to feeling stress, which in turn may generate a stress reaction. Livingston defines the stress reaction as increased sympathetic nervous system (SNS) activity and subsequent release of corticosteroid hormones. Anderson et al.’s (13) contextual model of hypertension additionally suggests that chronic stressors (such as poverty, racism, etc.) African Americans may specifically experience on a regular basis lead to the development of EH. Anderson et al. argue that chronic stressors interact with biological, behavioral, and psychological risk factors to increase SNS activity, which results in release of neuroendocrine hormones. Over time, repeated stress-induced episodes of heightened vascular reactivity may lead to structural change in the vascular wall, which in turn leads to the development of EH.

Violence exposure is an important environmental stressor that is prevalent among inner-city youth. Previous studies indicate that as many as 70% of inner-city youth have been victims of violent acts, including acts where others have threatened, chased, hit, beaten, sexually assaulted, or attacked them with a knife or gun (14). Additionally, 85% of these youth report having witnessed violent acts (15). There is strong evidence that children exposed to violence show both psychological and behavioral problems. For example, violence exposure is positively correlated with symptoms of depression, anxiety, posttraumatic stress disorder, and aggressive behavior in adolescents (15–20). Although research has linked violence exposure to psychological and behavioral problems in youth, no previous study has examined the association between violence exposure, SNS activity, and BP dipping status.

The mechanisms underlying the effects of violence exposure on ABP are unknown, although contextual models of EH would suggest that elevated SNS activity may be involved (21, 22). One potential means by which the SNS may mediate nondipping status is through its effect on peripheral vascular resistance. Previous studies on racial differences in cardiovascular hemodynamics, including studies involving adolescents, indicate a greater peripheral vascular reactivity in African American as compared with whites (23–27). In addition, within-population studies of cardiovascular hemodynamics in African Americans show greater peripheral vascular responses in offspring of hypertensives as compared with normotensives (28). Previous research has also shown that total peripheral resistance and norepinephrine responses to stress are greater in offspring of hypertensives than in of normotensives (23–27). Taken together, these studies suggest the presence of early preclinical changes in vascular reactivity that are most likely linked to heightened daytime SNS activity. Thus, nondippers may have elevated nighttime BP and increased vascular resistance in response to heightened daytime (and/or nighttime) sympathetic activation.

Several studies have confirmed that SNS activation occurs in individuals with elevated nighttime BP. For example, Kostic and Secen (27) reported significantly higher BP values during sleeping periods for patients with severe hypertension and in association with this significantly higher daytime and nighttime cortisol and urinary catecholamine excretion. James et al. (28) have also shown a positive association between nighttime BP and catecholamine excretion rate in normotensive working women. These data further support the catecholamine hypothesis and that the SNS may be one controlling influence on nondipping status.

To the best of our knowledge no previous study has examined the relationship between violence exposure, catecholamine excretion, and BP dipping status in African American adolescents. The present study expands on previous work by examining the association between violence exposure, catecholamine responses, and ABP responses (dipping status) in a sample of healthy male vs. female African American adolescents. Some research indicates that African American boys are exposed to more violence and life-threatening situations than African American girls (29). Furthermore, research from the Centers for Disease Control and Prevention indicates that 30% of high school boys carry a potentially lethal weapon around with them in the community and approximately 12.5% of these boys carry a weapon to school (30). Furthermore, some research suggests that boys may be more psychologically reactive to violence exposure than girls (16). Given these preliminary observations, we hypothesized that violence exposure would be associated with heightened SNS activation and nondipping status and that these responses would be greater in boys than in girls.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
Subjects
The study protocol was approved by the Committee on the Conduct of Human Research of Virginia Commonwealth University. Written informed consent was obtained from each participant. All participants were offered the option of speaking with a counselor after completing the study protocol. Healthy African American adolescents (age 11–18 years) were recruited from local schools in Richmond, Virginia. Each child participated in a health screening, which included BP assessment, assessment of a urine specimen (to rule out hematuria, glucosuria, and proteinuria), and measurement of height (cm) and weight (kg). All participants were within 30% of ideal body weight for their height. The sample consisted of 56 black adolescents (see Table 1).


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  		TABLE 1. Baseline and Demographic Measurementsa
 
Procedure
The study procedures were in accordance with institutional guidelines. Parents provided demographic and background information. Each subject’s casual BP was measured by a trained technician with a Dinamap BP apparatus (model 8100; Critikon Inc, Tampa, FL) as outlined by the Second Task Force on Blood Pressure Control in Children (31). After a 5-minute rest period, a total of five SBP and DBP measurements were taken with a 30-second interval between readings. The average of these five measurements was used to determine whether subjects were normotensive and eligible to participate in the study. Only normotensive adolescents who did not have preexisting cardiovascular or chronic disease and who were not taking medications (including oral contraceptives) met inclusion criteria to participate in the study. The definition of high BP (31) for the present study was 128/82 mm Hg for 11- to 12-year-olds, 136/86 mm Hg for 13- to 15-year-olds, and 142/92 mm Hg for 16- to 18-year olds.

Demographic and Background Information
Parents provided information on family history of EH and related illnesses. Parents indicated in a yes/no format whether anyone in the child’s immediate family who was a blood relative (father, mother, brother, sister, grandparents, uncles, and aunts) had hypertension or was currently taking medication for high BP. Parents also indicated their total annual family income on a scale ranging from 1 to 7 (1 = less than $10,000; 2 = $10,000–$19,999; 3 = $20,000–$29,999; 4 = $30,000–$39,999; 5 = $40,000–$49,999; 6 = $50,000–$59,999; 7 = $60,000 or more). Parents also provided information on their current marital status (ie, married, separated/divorced, or widowed).

Violence Exposure Measures
A modification of Richters and Saltzman’s Survey of Exposure to Community Violence (32) was used to measure adolescents’ exposure to violence. This measure contains approximately 16 different types of violence overall, including separate assessments for experiences of direct victimization and experiences of witnessing (either seeing or hearing about) violence occurring to others. Adolescents rated how often (0 = never to 4 = almost every day) they had been a victim of violence (11 items), had seen violence (18 items), or had heard about violence (16 items) in their community within the past year. Each participant was instructed to include only real-life situations, not events they may had seen or heard about on television or radio. Sample victimization items include "How may times have you yourself been beaten up or mugged?" and "How may times have you yourself been chased by gangs or older kids?" Sample items of witnessing violence include "How may times have you seen someone trying to force their way into somebody else’s house or apartment?" Sample items of hearing about violence include "How many times have you only heard about someone else being attacked or stabbed with a knife?" Separate indicators of victimization, seeing, and hearing about violence were available from the survey. Test-retest reliability for the total scale after 1 week is r = 0.81 (29). Validity analyses have indicated that the measure positively correlates with adjustment difficulties in African American youth (16).

ABP Monitoring
All subjects participated in the ABP protocol. Each participant was seated, and the ABP recorder (Advanced Biosensor Inc, Columbia, SC) was applied and calibrated. Three readings from the ABP recorder were compared with a mercury column to determine proper functioning of the recorder. If the technician was unable to match three readings to within ±5 mm Hg for SBP, then another recorder was applied and calibrated. Participants recorded their actual awake and asleep times and recorded any unusual events during the course of the 24-hour period. The recorder was set to take readings at 15-minute intervals over 24 hours. Once the recorder had been removed, the BP results were examined. If more than 25% of the measurements were artifacts or missing, the participant was asked to repeat the ABP recording.

Urine Collections for Catecholamine Determination
Subjects were required to collect two timed urine samples, 1 daytime and 1 nighttime, in separate collection bottles. Collection bottles and instructions (written and verbal) on proper procedures for obtaining the fractionated 24-hour urine samples were given to both the child and the parent by a trained technician. Subjects were instructed to begin the collection at 6:00 AM, at which time they voided into the toilet. After collecting their urine throughout the day they were instructed to record the time of their last urine collection before going to sleep. They were next instructed to collect their urine throughout the night in a second container and their last nighttime collection at 6:00 AM on awakening the next day. Urine containers were kept refrigerated during the entire collection procedure and were brought to the Virginia Commonwealth University Clinical Research Center. A nurse determined the volume of the collection. If the volume of the urine collection was less than 500 ml, the child was asked to repeat the procedure again. Subjects who met the following criteria were considered to have an adequate urine collection: 1) 24-hour urine volume >500 ml and 2) excretion of creatinine >10 mg/kg over 24 hours. Creatinine was measured with a Beckman Creatinine Analyzer 2 (Beckman Instruments Inc, Brea, CA). A total of 56 subjects provided adequate urine samples. Six subjects were excluded from the study because of inadequate urine collections.

Urine samples were analyzed by high-performance liquid chromatography with electrochemical detection to determine total epinephrine and norepinephrine. Means and standard errors for catecholamines are expressed as excretion rate (ng/min). The excretion rates were calculated multiplying the measured concentration (ng/ml) by the urine production rate (ml per collection interval), and this product was divided by the number of minutes in the collection interval.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
Subject Characteristics
Table 1 presents demographic and baseline characteristics for the entire sample by gender. There were no significant group differences on demographic or baseline measures. Note that the results for family history of hypertension did not change when aunts and uncles were excluded from the analyses in the definition of hypertension.

ABP Measurements
The data from the ABP recordings were edited according to previously published standards (33, 34). Average awake and asleep SBP and DBP values were then determined for each participant on the basis of the subject’s self-report of awake and asleep times. A series of t test comparisons indicated that boys had higher nighttime SBP than girls (p < .03; see Table 2).


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  		TABLE 2. Daytime and Nighttime Ambulatory Blood Pressure, Catecholamine Excretion, and Violence Exposure
 
Adolescents were classified as dippers or nondippers separately for MBP (SBP + 2DBP/3). Because our two previous independent studies indicated approximately a 30% rate of nondipping status among African American adolescents (4, 5), we selected MBP as the classification variable since this measure seemed the most reliable indicator of nondipping status (nondipping status prevalence rates in present sample: MBP = 23.2%, SBP = 44.6%, and DBP = 10.7%). Participants were classified as dippers if their MBP showed a 10% or greater decrease from awake to asleep and as nondippers if their MBP showed a decrease of less than 10% from awake to asleep. {chi}2 testing indicated a significant difference between boys and girls in nondipping status, with a greater percentage of boys than girls classified as nondippers (37% vs. 10%; p < .03). Follow-up analyses indicated that there were no significant differences across dippers and nondippers in terms of sleep duration. One subject who was classified as a dipper recorded in the diary that she did not sleep during the nighttime hours.

Catecholamine and Violence Exposure Measurements
Table 2 shows epinephrine and norepinephrine excretion (in ng/min) for nighttime and daytime collections separated by males and females. {chi}2 testing indicated that boys had significantly greater epinephrine excretion (p < .001) and norepinephrine excretion (p < .05) during the daytime than did girls. Level of violence exposure was also compared for boys and girls. There were no significant sex differences in hearing about violence, seeing violence, or in victimization during the past year (Table 2).

Correlational Analyses
Correlational analyses were performed to determine the zero-order relations between daytime and nighttime ABP, epinephrine and norepinephrine excretion, violence exposure (victimization, seeing violence, and hearing about violence), and demographic variables (age, sex, Quetelet Index, family history of hypertension, annual family income, and marital status of parents). Table 3 presents the correlations for the primary variables of interest. MBP dipping status was positively associated with victimization experiences (r = 0.42; p < .0001). Both seeing and hearing about violence were also positively associated with higher levels of daytime epinephrine excretion (r = 0.28 and 0.32, respectively; p < .05 for both), and hearing about violence was positively associated with daytime norepinephrine excretion (r = 0.29; p < .05). There were no significant associations between MBP dipping status or catecholamine excretion with family history of hypertension, annual family income, or parents’ marital status (not shown in Table 3). Data regarding family history of hypertension, annual family income, and family structure were available for 40 participants.


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  		TABLE 3. Correlations Between Violence Exposure, Ambulatory Blood Pressure, Epinephrine Excretion, Norepinephrine Excretion, and Controlsa
 
Data Analyses
Several sets of regression analyses were run to evaluate the contributions of violence exposure to catecholamine excretion and MBP dipping status. In each set of analyses, age, sex, and Quetelet Index (kg/m2) were controlled for because of their association with the outcome measures. Separate models were run for each indicator of violence exposure (victimization, hearing about violence, and seeing violence). Interactions with sex were included in these models to explore the hypothesis that violence exposure might have different impacts on the physiological responses of males vs. females.

Regression Analyses Predicting Catecholamine Excretion
In the first set of analyses, daytime epinephrine was the outcome variable. Age, sex, and Quetelet Index were entered on the first step; followed by violence exposure (one of the three indicators: victimization, seeing violence, or hearing about violence) on the second step; and the violence exposure by sex interaction on the final step. All continuous-level predictor and control variables were centered before entry, and interaction terms were formed using these centered variables (35). For the analyses with hearing about violence as the predictor, there was a significant violence by sex interaction (standardized ß = 0.40, t = 2.64, p < .02) with the model explaining 43% of the variance in daytime epinephrine (model F(5,46) = 6.80, p < .001). Plots of this analysis (Fig. 1) indicated that there was a strong, positive association between hearing about violence and daytime epinephrine for males (partial correlation = 0.59, p < .05) and no relation for females (partial correlation = 0.03, p = NS). The above analyses were repeated with daytime norepinephrine, nighttime epinephrine, and nighttime norepinephrine as the outcome measure. No other effects were significant.



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  		Fig. 1. Interaction of hearing about violence and sex predicting daytime epinephrine (ng/min) levels.

 
Logistic Regression Analyses Predicting MBP Dipping Status
In the next set of analyses, logistic regression was used to predict MBP dipping status. As before, age, sex, and Quetelet Index were entered on the first step; followed by violence exposure (one of the three indicators) on the second step; and the violence exposure by sex interaction on the final step. Continuous-level predictor and control variables were centered before entry, and interaction terms were formed on the basis of these centered values.

Table 4 presents the results of the three main logistic regression analyses. Results of analyses with victimization as the exposure measure are presented in the first column of Table 4. As seen in this table, victimization was positively associated with MBP dipping status, but the interaction with sex was not significant. Eighty-two percent of the cases in this analysis were correctly classified. Odds ratio analyses indicated that nondippers were 9 times more likely than dippers to have experienced some victimization in the past year (OR = 9.0, p < .05).


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  		TABLE 4. Step and Final Model Unstandardized ß Values, Standard Errors, and Wald Values for Blood Pressure Dipping Status: Hierarchical Logistic Regression Analysis
 
Column 2 of Table 4 presents the results of analyses with seeing violence as the exposure measure. As indicated in the table, there was a marginally significant (p < .06) interaction of seeing violence and sex for predicting MBP dipping status. Seeing violence in the community was associated in different directions with MBP dipping status in males and females, with male nondippers reporting the greatest exposure. Eighty-three percent of the cases in this analysis were correctly classified. Odds ratio analyses indicated that nondippers were nearly 3.5 times more likely to have seen violence during the past year compared with dippers (OR = 3.45, p < .05).

As shown in column 3 of Table 4, there was a significant interaction for hearing about violence by sex predicting MBP dipping status (p < .05). Figure 2 illustrates that hearing about violence in the community was associated in different directions with MBP dipping status in males and females, with male nondippers reporting the greatest exposure. Seventy-eight percent of the cases in this analysis were correctly classified. Odds ratio analyses indicated that nondippers were 1.2 times more likely than dippers to have heard about violence during the last year (OR = 1.2, p = NS).1



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  		Fig. 2. Self-reported exposure of hearing about violence during the past year separated by sex and MBP dipping status.

 
Analyses With Epinephrine as a Mediator of Violence Exposure and MBP Dipping Status
A final analysis was run to evaluate the hypothesis that daytime epinephrine levels mediate the violence exposure (hearing about violence) by sex interaction predicting BP dipping status. According to Barron and Kenny (36), several criteria must be met to establish mediation. First, the predictor(s) must be associated with the outcome. Second, the predictor(s) must be associated with the hypothesized mediator. Third, the hypothesized mediator must be associated with the outcome. Fourth, the predictor(s) must no longer be associated with the outcome once the mediator was controlled. In this case, there was a significant violence exposure (hearing about violence) by sex interaction to be explained, meeting the first criterion. As noted above, there was a significant violence exposure (hearing about violence) by sex interaction predicting daytime epinephrine, meeting the second criterion. Daytime epinephrine levels, however, were not significantly correlated with MBP dipping status (Table 3), so the third criterion for mediation could not be established. This suggests that elevated daytime epinephrine did not directly mediate the relationship between violence exposure (hearing about violence) and MBP dipping status in males vs. females.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
This study is the first to demonstrate that victimization was positively associated with MBP nondipping status in both male and female African American adolescents. Boys showed a greater prevalence of MBP nondipping status and elevated daytime epinephrine excretion than did girls. There was also a violence exposure (hearing about violence) by sex interaction predicting MBP dipping status. Hearing about violence in the past year was positively associated with MBP nondipping status among male but not female African American adolescents. No main effects for sex or hearing about violence were demonstrated. Furthermore, catecholamines did not mediate the violence exposure (hearing about violence) by sex interaction predicting MBP dipping status.

Overall, self-reported victimization was positively associated with MBP nondipping status in both boys and girls. This finding is consistent with previous studies that demonstrate a greater degree of peripheral vascular reactivity in African Americans than whites in response to hemodynamic stress (22–25). Furthermore, these data are consistent with Anderson’s contextual model of EH in African Americans. According to Anderson et al. (13, 22, 25), chronic stressors interact with biological, behavioral, and psychological risk factors to increase SNS activity. Specifically, exposure to chronic stressors (eg, poverty, residential crowding, and substandard housing) is more common among African Americans (37–42) and may increase neuroendocrine activity and sodium retention through specific behavioral and psychological factors (ie, hostility and anger expression). Coping data were available for a subsample of the youth in the present study. Those adolescents who were classified as nondippers in the study were significantly less likely than dippers to report using behavioral strategies (p < .05) to cope with the violence they had experienced, seen, or heard about, indicating they were less actively dealing with this environmental stressor. A wide body of literature has shown that actively engaging with a stressor is associated with positive mental and physical well-being, whereas the opposite is true of avoidant strategies (43).

In the present study, there was a violence exposure (hearing about violence) by sex interaction predicting MBP dipping status. No main effects for sex or hearing about violence were demonstrated. Hearing about violence was, however, associated with elevated daytime epinephrine and MBP nondipping status in boys but not girls. These findings are somewhat consistent with Harshfield et al.’s (33, 34) studies, which show greater nighttime SBP and DBP among African American adolescent boys as compared with girls. Little is known, however, about sex differences in stress exposure and adjustment. McLean et al. (44) reported sex differences in hemodynamic responses in young healthy subjects. Males showed greater increases in SBP and DBP to hand immersion stress than did females, but sex differences were not found in heart rate or plasma norepinephrine responses. Similarly, Pettit et al. (45) found greater increases in stroke volume after cold air exposure (sitting at rest in 5°C for 2 hours) in men as compared with women, but differences were not accounted for by body fatness or catecholamine responses. In addition, the majority of studies on sex differences and BP nondipping status have not demonstrated consistent differences between males and females (46–49); however, few of these studies have focused on African American populations.

Sex differences in catecholamine excretion may reflect different stress levels and/or ineffective coping mechanisms with possible residual increased SNS activity at night influencing BP dipping status. Sex differences in socialization processes may, in part, explain the variation in catecholamine responses across boys and girls in the present study. For example, socialization processes differ markedly for African American boys and girls, with boys being reinforced for being more independent, self-reliant, and self-assured than girls (50). The day-to-day life experiences may also differ across African American boys and girls. For example, African American boys experience more violence and more life-threatening situations than African American girls (50, 51). Previous research by Wilson et al. (52) has shown that violence exposure in African American adolescents was positively associated with elevated nighttime BP, although no sex differences were reported. An alternative explanation might be that boys with particular physiological characteristics (increased daytime catecholamines, MBP nondipping status) are more likely to remember hearing about violence or may even initiate conversations about it so that they hear more about violence. In contrast, girls with the same physiological characteristics may have a different behavior profile, such as avoiding talking about violence-related events. It is also possible that hearing about violence is interpreted differently by males and females.

It is important to note that the catecholamine excretion rates reported in the present study are comparable to those reported in other studies that have examined physiological stress responses among minority populations. For example, Brown and James (53) reported urinary norepinephrine excretion rates ranging from 16.7 ± 21.5 to 29.8 ± 13.0 ng/min and epinephrine excretion rates ranging from 2.7 ± 6.2 to 7.0 ± 4.8 ng/min in a study examining stress responses in Filipino-American immigrant nurses. In the present study norepinephrine levels ranged from 15.5 ± 13.4 to 29.2 ± 25.1 ng/min, and epinephrine levels ranged from 2.4 ± 4.1 to 5.1 ± 3.4 ng/min. Thus, the catecholamine values obtained in this adolescent outpatient study seem comparable to other standards. Thus, this seems a feasible method for further investigating physiological stress responses in adolescent populations.

There are several limitations to the present study. First, the study was cross-sectional in nature; thus, no causal interpretations can be made. Furthermore, the generalizability of the study may be limited due the relatively small number of participants. The reliability of MBP dipping status may also be questioned given that only one 24-hour ABP measure was used in the present study. Previous investigators have observed that caution should be used in classifying subjects as either dippers or nondippers on the basis of one 24-hour ABP measurement (54). In our previous work we demonstrated that 82% of African American adolescents were consistently classified as nondippers across SBP, DBP and MBP measures (5). Further research is needed, however, to determine the reproducibility of BP dipping patterns when repeated ABP assessments are obtained in an outpatient setting. Nighttime BP may have remained high for some participants because they were moving restlessly in bed or even getting up during the night; however, diary records indicated that only one participant, who was classified as a dipper, reported not sleeping while wearing the ABP monitor. With these limitations in mind, this study is the first to demonstrate that violence exposure (victimization and hearing about violence) was associated with MBP nondipping status in male and female African American adolescents.

In summary, MBP nondipping was associated with victimization, and boys who report higher levels of hearing about violence were more likely to be nondippers, placing them at higher risk for developing hypertension in early adulthood. Although this study demonstrated a greater prevalence of MBP nondipping in males who reported high levels of hearing about violence, increased daytime epinephrine did not directly mediate the effects of sex and violence on MBP nondipping status. Thus, the precise physiological mechanisms that underlie these observations are presently undefined and should be the focus of future investigations.


   ACKNOWLEDGMENTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
REFERENCES
 
This project was supported by an A. D. Williams Grant from the Virginia Commonwealth University to the first author and by General Clinical Research Center (GCRC) Grant M01RR00065 at Virginia Commonwealth University.


   NOTES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
ACKNOWLEDGMENTS
 REFERENCES
 
1 Analyses predicting SBP dipping status showed no main effects for victimization, seeing violence, or hearing about violence. There was a marginally significant interaction for hearing about violence by sex predicting SBP dipping status (p < .06). Hearing about violence in the community was associated in different directions with SBP dipping status in males and females, with male nondippers reporting the greatest exposure. Analyses predicting DBP dipping status showed no significant main effects or interactions. Back

Received for publication April 24, 2001.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 

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