Circulating levels of glucocorticoid hormones in WHHL and NZW rabbits: circadian cycle and response to repeated social encounter.

Social environment influences the progression of atherosclerosis in an important experimental model of disease, the Watanabe Heritable Hyperlipidemic rabbit (WHHL). Although the hypothalamic-pituitary-adrenocortical (HPA) system is likely to play an important role in the behavioral modulation of disease, relatively little is known about the glucocorticoid responses in these animals, or in other strains of rabbits. The purpose of the present study was to: (1) evaluate the rabbit glucocorticoid circadian rhythm, (2) compare plasma cortisol and corticosterone responses to social stress, and (3) examine strain differences (i.e., WHHL vs. New Zealand White (NZW)) in rabbit glucocorticoid responses to assess whether WHHLs have an aberrant HPA system. It was found that male rabbits secrete both corticosterone and cortisol in a circadian rhythm that peaks in the afternoon and reaches a nadir at 0600 h, i.e., approximately 12 h out-of-phase with the human glucocorticoid rhythm. Both glucocorticoids responded similarly to social stress induced by repeated daily 4 h pairings with another male rabbit; after 10 days of pairings, glucorticoid values were significantly correlated with the amount of defensive agonistic behavior exhibited. Finally, there were no significant strain differences in glucocorticoid circadian rhythms, baselines, or responses to social stress. These data suggest that glucocorticoid responses (i.e., circadian rhythms, responses to social stress) in the WHHL are similar to glucocorticoid responses in standard laboratory white rabbits.

Piecewise latent growth curve modeling of systolic blood pressure reactivity and recovery from the cold pressor test.

Latent growth curve methodology was used to model systolic blood pressure reactivity and recovery from the cold pressor test. A piecewise regression approach permitted the separate but simultaneous modeling of the two components (reactivity and recovery) of the stress process. Data came from a study of 99 participants classified on the basis of gender, ethnicity, and family history of hypertension. Their systolic blood pressure was assessed at rest, during the cold pressor test, and during a task recovery period. A measure of task appraisal and readings from ambulatory blood pressure monitoring during a workday were also examined. The article illustrates a step-by-step approach to modeling reactivity and recovery. Results indicated that both reactivity and recovery were associated with subsequent systolic blood pressure at work.

Validation of the insulin sensitivity index (ISI(0,120)): comparison with other measures.

The purpose of this study was to explore possible calculations using oral glucose tolerance test (OGTT) values in order to develop a simple measure of insulin sensitivity. We devised a formula for an insulin sensitivity index, ISI(0,120), that uses the fasting (0 min) and 120 min post-oral glucose (OGTT) insulin and glucose concentrations. It appears to be generalizable across a spectrum of glucose tolerance and obesity. Most importantly, our data show that ISI(0,120) correlates well, when applied prospectively in comparative studies, with the insulin sensitivity index obtained from the euglycemic hyperinsulinemic clamp (r = 0.63, P < 0.001). This correlation was demonstrably superior to other indices of insulin sensitivity such as the HOMA formula presented by Matthews, and performed comparably to the computerized HOMA index. Measurement of insulin sensitivity has traditionally been possible only in research settings because of the invasiveness and expense of the methods used. Clinical investigators have therefore sought more practical methods to obtain an index of insulin sensitivity. Such an index should approximate insulin sensitivity as measured by the euglycemic hyperinsulinemic clamp (M). We present ISI(0,120), a simple yet sensitive measure of insulin sensitivity which is adaptable for use in clinical settings as well as large epidemiologic studies.

Differential patterns of dynamic cardiovascular regulation as a function of task.

In cardiovascular reactivity studies, interpretations of the processes supporting the blood pressure response may become problematic when systolic blood pressure, diastolic blood pressure, and heart rate all increase in response to a behavioral challenge. Therefore, in addition to evaluating these cardiovascular responses, this study examined cardiac output, total peripheral resistance and systolic time intervals derived from impedance cardiogram, electrocardiogram and phonocardiogram recordings during a speech stressor, a mirror tracing task, and a foot cold pressor test. All of the behavioral stressors elicited increases in blood pressure and heart rate, with the largest changes occurring during the overt speech. Based on the examination of the response patterns of the underlying hemodynamic variables it would appear that, in both men and women, the blood pressure increase during the speech preparation period was supported by increased cardiac output; the speech itself resulted in a mixed pattern of increased cardiac output and total peripheral resistance; whereas, the mirror tracing and cold pressor tasks produced increased total peripheral resistance. Although men and women produced similar response patterns to the behavioral challenges, sex differences in the estimates of myocardial contractility were observed during rest. These results provide evidence that different behavioral stressors can produce a distinct yet integrated pattern of responses, whose differences may be revealed, when impedance cardiography is used, to derive sufficient response measures for assessing dynamic cardiovascular processes.

The influence of social situations on ambulatory blood pressure.

Ambulatory blood pressure (BP) levels were assessed and types of activities were recorded every 20 min for a 12-hr period in 131 normotensive or mild-moderate hypertensive subjects. Systolic (S)BP and diastolic (D)BP levels varied significantly as a function of the social situation (alone, with family, with friends, or with strangers). BP levels were lowest when subjects were with family and were highest when subjects were with strangers.

The reliability and specificity of delta versus residualized change as measures of cardiovascular reactivity to behavioral challenges.

The statistical parameters that influence the reliability of delta and residualized change were examined in the context of the assessment of cardiovascular reactivity. A comparison of the relative reliabilities of these two quantification methods was performed using systolic blood pressure, diastolic blood pressure, and heart rate data from two samples of 134 and 109 subjects observed during baseline and either two or four behavioral challenges. The results indicated that both delta and residualized change scores can yield reliable measures of blood pressure and heart rate reactivity to behavioral challenges, and that their reliabilities will be comparable under the conditions observed in laboratory reactivity studies. Correlations between baseline and delta did not indicate that these two measures were systematically related. Finally, delta scores are more appropriate than residuals when assessing the generalizability of responses across a variety of tasks.

Race and blood pressure status influences cardiovascular responses to challenge.

The influence of race and blood pressure status on cardiovascular responses to three challenges (interview, video game and cold pressor) was investigated in 50 healthy normotensive and 30 unmedicated mild-to-moderate hypertensive black and white men, aged 25-44 years old. Group differences were obtained for two tasks. The interview evoked race and blood pressure status differences: higher heart rate responses were elicited from normotensives compared with hypertensives and larger diastolic blood pressure (DBP) responses were elicited from whites compared with blacks. For the video game, black hypertensives displayed larger DBP responses than white hypertensives and greater systolic blood pressure and DBP responses than black normotensives. The video game heart rate response of white normotensives exceeded that of black normotensives and white hypertensives. These findings suggest that cardiovascular responses to challenge are affected by race and blood pressure status. The blood pressure hyperresponsiveness of black hypertensives compared with black normotensives to a psychological challenge (video game) provides generality to previous research conducted only on whites.

Predicting home and work blood pressure measurements from resting baselines and laboratory reactivity in black and white Americans.

The relationship between blood pressure in the laboratory (both at rest and in response to laboratory tasks) and ambulatory blood pressure at home and at work was evaluated. One hundred nineteen normotensive and unmedicated mild-moderate hypertensive black and white females and males participated in laboratory blood pressure monitoring at rest and during four challenging tasks (structured interview, video game, bicycle exercise, and cold pressor test) as well as ambulatory blood pressure monitoring while at home and at work. Baseline blood pressure taken while subjects were at rest was the strongest predictor of ambulatory systolic blood pressure (r = .64) and diastolic blood pressure (r = .77) at work. Among reactivity tasks the strongest predictors of ambulatory blood pressure in the total population were the structured interview and the video game (both psychological tasks) followed by the cold pressor test. Racial comparisons, however, determined that the cold pressor test predicted diastolic blood pressure significantly better for blacks (r = .73) than for whites (r = .40), suggesting a possible difference in blood pressure regulation.

Cardiovascular and neurohumoral responses to behavioral challenge as a function of race and sex.

Cardiovascular and hormonal responses to a structured interview, an electronic video game, a cold pressor test, and exercise on a bicycle ergometer were assessed in eighty-three 25- to 44-year-old normotensive Black and White men and women. Blacks showed significantly greater diastolic blood pressure (DBP) responses than Whites during the cold pressor test, which were not accounted for by an increase in plasma catecholamines. Exercise produced reliably greater systolic blood pressure (SBP) increases in Black women than in Black men or White women. Men showed significantly greater SBP and DBP changes than women during the video game. These findings suggest that the pattern of physiological reactivity elicited by challenge is related to the race and sex of the subjects.

Associations of blood pressure with self-report measures of anger and hostility among black and white men and women.

This study examined associations between blood pressure (BP) and dispositional variables pertaining to anger and hostility. Black and White 25- to 44-year old male and female normotensives and unmedicated mild to moderate hypertensives completed four reliable self-report scales--the Cook-Medley Hostility (Ho) Scale, the Trait Anger subscale of the State-Trait Anger Scale (STAS-T), and the Cognitive Anger and Somatic Anger subscales of the Cognitive-Somatic Anger Scale--plus the Framingham Anger Scale and the Harburg Anger Scale. They also engaged in three laboratory tasks--Type A Structured Interview (SI), a video game, and a cold pressor task--that elicit cardiovascular reactivity. Ambulatory BP readings at home and at work were also obtained from most subjects. Blacks had significantly higher Ho and lower STAS-T scores than did Whites. Women reported higher levels of somatic anger than did men. White women showed significant positive correlations between STAS-T and systolic BP (SBP) and diastolic BP (DBP) both at rest in the laboratory and during the SI. Black women revealed significant positive relationships between STAS-T and SBP and DBP at rest in the laboratory and at work as well as with DBP during the cold pressor test. For Black men, cognitive anger and DBP at rest were positively related. In contrast, White men revealed significant negative correlations between Ho scores and SBP at rest and during the video game; these men also showed significant negative relationships between somatic anger and SBP and DBP reactivity during the cold pressor test. Women, but not men, showed significant positive relationships between all four anger measures and ambulatory BP at work. Whereas main effects relating anger and cardiovascular measures were not apparent as a function of race, Blacks demonstrated significantly greater SBP and DBP reactivity than Whites during the cold pressor test, with the converse occurring during the SI. Men demonstrated significantly greater DBP reactivity than women during the video game. The present findings indicate that self-reports on anger/hostility measures and cardiovascular responses to behavioral tasks differ as a function of race but that relationships between anger and BP regulation need to take into account possible race-sex interactions and selection of anger/hostility measures.

Blood pressure stability of normotensives and mild hypertensives in different settings.

Generalizability theory was used to examine the stability of blood pressure (BP) measurement in normotensives and mild hypertensives. Three to six readings at home or at work provided adequate reliability for the same day in each setting. Under structured laboratory conditions, two to three BP measures taken on each of 2 to 3 days for systolic and diastolic BP provided conservative estimates that were generalizable across days. Finally, generalizations across settings called for five or more measurements taken in at least two settings.