Status, stress, and atherosclerosis: the role of environment and individual behavior

Mental stress and coronary artery disease: a multidisciplinary guide

Research suggests that acute and chronic stress are risk factors for the development and progression of coronary artery disease. Much of this work is multidisciplinary, using unfamiliar concepts deriving from disciplines other than cardiology and medicine. This article addresses and clarifies, for the cardiologist, some of the key concepts and issues in this area and provides an overview of evidence linking acute and chronic stress to cardiac pathology. Areas addressed include definitions and measurement of mental stress, methodological issues in stress research, and distinctions between stress and variables such as personality, emotion, and depression. Mental stress is a multifactorial process involving the environment, individual experiences and coping, and a set of neuroendocrine, autonomic, cardiovascular, and other systemic physiologic responses. There are difficulties identifying a single consensus physiologic stress measure because of individual differences in perceptions and physiologic response patterns. Nonetheless, important associations exist between mental stress and clinically relevant cardiovascular end points. As multidisciplinary research in this area continues, one major goal is the better integration of psychosocial knowledge and measures with cardiology research and practice.

Old World Nonhuman Primate Models of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is a major health problem of increasing incidence. To better study the pathogenesis and potential therapeutic agents for this disease, appropriate animal models are needed. Old World nonhuman primates (NHPs) are a useful animal model of type 2 diabetes; like humans, the disease is most common in older, obese animals. Before developing overt diabetes, NHPs have a period of obesity-associated insulin resistance that is initially met with compensatory insulin secretion. When either a relative or absolute deficiency in pancreatic insulin production occurs, fasting glucose concentrations begin to increase and diabetic signs become apparent. Pathological changes in pancreatic islets are also similar to those seen in human diabetics. Initially there is hyperplasia of the islets with abundant insulin production typically followed by replacement of islets with islet-associated amyloid. Diabetic NHPs have detrimental changes in plasma lipid and lipoprotein concentrations, lipoprotein composition, and glycation, which may contribute to progression of atherosclerosis. As both the prediabetic condition (similar to metabolic syndrome in humans) and overt diabetes become better defined in monkeys, their use in pharmacological studies is increasing. Likely due to their genetic similarity to humans and the similar characteristics of the disease in NHPs, NHPs have been used to study recently developed agonists of the peroxisome proliferators-activated receptors. Importantly, agonists of the different receptor subclasses elicit similar responses in both humans and NHPs. Thus, Old World NHPs are a valuable animal model of type 2 diabetes to study disease progression, associated risk factors, and potential new treatments.

Social disadvantage and adolescent stress

PURPOSE

Low socioeconomic status (SES) and minority race/ethnicity are both associated with chronic stress and co-vary in American society. As such, these factors are often used synonymously, without clear theoretical conceptualization of their roles in the development of stress-related health disparities. This study theorized that race/ethnicity and SES reflect social disadvantage, which is the underlying factor in the development of stress-related illness, and examined how social disadvantage, defined in terms of both race/ethnicity and SES, influences adolescents' stress.

METHODS

This is a cross-sectional school-based study of 1209 non-Hispanic black and white 7th-12th graders from a single Midwestern metropolitan public school district. Each student completed a questionnaire and a parent provided SES information. Race/ethnicity was obtained from school records. Linear regression analyses determined the influence of race/ethnicity and SES to stress. Race/ethnicity and presence or absence of at least one parent who graduated from college were used to define four subgroups for within-group analyses.

RESULTS

Stress was higher among black students, those from lower SES families, and those with lower perceived SES. In subgroup analyses, neither race nor SES maintained their independent associations with stress among socially disadvantaged groups. Black race was not associated with stress among those without a college-educated parent, and parent education did not influence stress among black students. In contrast, among more socially advantaged groups, both SES and race explained variation in adolescents' stress.

CONCLUSIONS

Social disadvantage is associated with increased stress, regardless of whether disadvantage is defined in terms of race or SES. This suggests that race and SES measure adversity in the social environment, and therefore, serve as risk markers, rather than risk factors. Future research should focus on the experience of adversity, which is reflected by these social characteristics, and the processes by which it operates.

Assessment of the relative reinforcing strength of cocaine in socially housed monkeys using a choice procedure

Position in the social hierarchy can influence brain dopamine function and cocaine reinforcement in nonhuman primates during early cocaine exposure. With prolonged exposure, however, initial differences in rates of cocaine self-administration between dominant and subordinate monkeys dissipate. The present studies used a choice procedure to assess the relative reinforcing strength of cocaine in group-housed male cynomolgus monkeys with extensive cocaine self-administration histories. Responding was maintained under a concurrent fixed-ratio 50 schedule of food and cocaine (0.003-0.1 mg/kg per injection) presentation. Responding on the cocaine-associated lever increased as a function of cocaine dose in all monkeys. Although response distribution was similar across social rank when saline or relatively low or high cocaine doses were the alternative to food, planned t tests indicated that cocaine choice was significantly greater in subordinate monkeys when choice was between an intermediate dose (0.01 mg/kg) and food. When a between-session progressive-ratio procedure was used to increase response requirements for the preferred reinforcer (either cocaine or food), choice of that reinforcer decreased in all monkeys. The average response requirement that produced a shift in response allocation from the cocaine-associated lever to the food-associated lever was higher in subordinates across cocaine doses, an effect that trended toward significance (p = 0.053). These data indicate that despite an extensive history of cocaine self-administration, most subordinate monkeys were more sensitive to the relative reinforcing strength of cocaine than dominant monkeys.

Potential for Unintended Consequences of Environmental Enrihment for Laboratory Animals and Research Results

Many aspects of the research animal's housing environment are controlled for quality and/or standardization. Of recent interest is the potential for environmental enrichment to have unexpected consequences such as unintended harm to the animal, or the introduction of variability into a study that may confound the experimental data. The effects of enrichment provided to nonhuman primates, rodents, and rabbits are described to illustrate that the effects can be numerous and may vary by strain and/or species. Examples of parameters measured where no change is detected are also included because this information provides an important counterpoint to studies that demonstrate an effect. In addition, this review of effects and noneffects serves as a reminder that the provision of enrichment should be evaluated in the context of the health of the animal and research goals on a case-by-case basis. It should also be kept in mind that the effects produced by enrichment are similar to those of other components of the animal's environment. Although it is unlikely that every possible environmental variable can be controlled both within and among research institutions, more detailed disclosure of the living environment of the subject animals in publications will allow for a better comparison of the findings and contribute to the broader knowledge base of the effects of enrichment.

The Darwinian concept of stress: benefits of allostasis and costs of allostatic load and the trade-offs in health and disease

Why do we get the stress-related diseases we do? Why do some people have flare ups of autoimmune disease, whereas others suffer from melancholic depression during a stressful period in their life? In the present review possible explanations will be given by using different levels of analysis. First, we explain in evolutionary terms why different organisms adopt different behavioral strategies to cope with stress. It has become clear that natural selection maintains a balance of different traits preserving genes for high aggression (Hawks) and low aggression (Doves) within a population. The existence of these personality types (Hawks-Doves) is widespread in the animal kingdom, not only between males and females but also within the same gender across species. Second, proximate (causal) explanations are given for the different stress responses and how they work. Hawks and Doves differ in underlying physiology and these differences are associated with their respective behavioral strategies; for example, bold Hawks preferentially adopt the fight-flight response when establishing a new territory or defending an existing territory, while cautious Doves show the freeze-hide response to adapt to threats in their environment. Thus, adaptive processes that actively maintain stability through change (allostasis) depend on the personality type and the associated stress responses. Third, we describe how the expression of the various stress responses can result in specific benefits to the organism. Fourth, we discuss how the benefits of allostasis and the costs of adaptation (allostatic load) lead to different trade-offs in health and disease, thereby reinforcing a Darwinian concept of stress. Collectively, this provides some explanation of why individuals may differ in their vulnerability to different stress-related diseases and how this relates to the range of personality types, especially aggressive Hawks and non-aggressive Doves in a population. A conceptual framework is presented showing that Hawks, due to inefficient management of mediators of allostasis, are more likely to be violent, to develop impulse control disorders, hypertension, cardiac arrhythmias, sudden death, atypical depression, chronic fatigue states and inflammation. In contrast, Doves, due to the greater release of mediators of allostasis (surplus), are more susceptible to anxiety disorders, metabolic syndromes, melancholic depression, psychotic states and infection.

Social factors and individual vulnerability to chronic stress exposure

The stress-response is adaptive in the short-term, but it can be maladaptive if sustained levels of its mediators are chronically maintained. Furthermore, not all individuals exposed to chronic stress will progress to disease. Thus, understanding the causes of individual differences and the consequences of variation in vulnerability is of major importance. The aim of this review is to shed light on this issue by presenting a new naturalistic model of chronic psychosocial stress in male mice. Resident/intruder pairs of mice lived in continuous sensory contact and physically interacted daily. Four categories were identified: Resident Dominant, Resident Subordinate (RS), Intruder Dominant, and Intruder Subordinate. Behavior, autonomic and immune functions, hypothalamic-pituitary-adrenocortical responses, brain cytokine expression and cardiac histology were investigated in stress-exposed mice. Certain stress-induced alterations were present in all mice independent of their social status, while others clearly differentiated dominants from subordinates. RS mice showed a unique profile of alterations suggesting that the loss of relevant resources, such as the territory, is the key factor determining why only certain stress-exposed individuals ultimately show malignancy and psychopathologies.

Sociotropic cognition moderates stress-induced cardiovascular responsiveness in women through effects on total peripheral resistance, but not cardiac output

Although cardiovascular disease (CVD) remains the leading cause of mortality in women, few studies have examined the role of psychosocial factors in its development. This study examined the moderating effects of sociotropic cognition (SC), a need for social acceptance and approval, on psychosocial stress-induced cardiovascular responsiveness (CVR) and affect reactivity in women. Sixty-eight normotensive, college-aged females were randomly assigned to a low or high social threat condition. Measures of systolic, diastolic and mean arterial blood pressures (SBP, DBP and MAP, respectively), heart rate (HR), cardiac output (CO), total peripheral resistance (TPR) and negative affect were collected during rest, and under conditions of high vs. low interpersonal threat. A two-step hierarchical regression analysis was performed to predict all response variables (BPs, HR, CO, TPR and affect). Increases in SBP, DBP, MAP, TPR and negative affect were greater in the high threat than low threat condition. Changes in SBP, MAP and TPR positively covaried with SC under conditions of high interpersonal threat, but showed no significant covariation in the low threat condition. The data suggest that an excessive need for social acceptance may contribute to rises in BP through an increase in TPR, but not CO under conditions of high social threat.

Characterization of dopamine D1 and D2 receptor function in socially housed cynomolgus monkeys self-administering cocaine

RATIONALE

Social rank has been shown to influence dopamine (DA) D(2) receptor function and vulnerability to cocaine self-administration in cynomolgus monkeys. The present studies were designed to extend these findings to maintenance of cocaine reinforcement and to DA D(1) receptors.

OBJECTIVE

Examine the effects of a high-efficacy D(1) agonist on an unconditioned behavior (eyeblinking) and a low-efficacy D(1) agonist on cocaine self-administration, as well as the effects of cocaine exposure on D(2) receptor function across social ranks, as determined by positron emission tomography (PET).

METHODS

Effects of the high-efficacy D(1) agonist SKF 81297 and cocaine (0.3-3.0 mg/kg) on spontaneous blinking were characterized in eight monkeys during 15-min observation periods. Next, the ability of the low-efficacy D(1) agonist SKF 38393 (0.1-17 mg/kg) to decrease cocaine self-administration (0.003-0.1 mg/kg per injection, IV) was assessed in 11 monkeys responding under a fixed-ratio 50 schedule. Finally, D(2) receptor levels in the caudate and putamen were assessed in nineteen monkeys using PET.

RESULTS

SKF 81297, but not cocaine, significantly increased blinking in all monkeys, with slightly greater potency in dominant monkeys. SKF 38393 dose-dependently decreased cocaine-maintained response rates with similar behavioral potency and efficacy across social rank. After an extensive cocaine self-administration history, D(2) receptor levels did not differ across social ranks.

CONCLUSIONS

These results suggest that D(1) receptor function is not substantially influenced by social rank in monkeys from well-established social groups. While an earlier study showed that dominant monkeys had higher D(2) receptor levels and were less sensitive to the reinforcing effects of cocaine during initial exposure, the present findings indicate that long-term cocaine use changed D(2) receptor levels such that D(2) receptor function and cocaine reinforcement were not different between social ranks. These findings suggest that cocaine exposure attenuated the impact of social housing on DA receptor function.

Effects of chronic psychosocial stress on cardiac autonomic responsiveness and myocardial structure in mice

Repeated single exposures to social stressors induce robust shifts of cardiac sympathovagal balance toward sympathetic dominance both during and after each agonistic interaction. However, little evidence is available regarding possible persistent pathophysiological changes due to chronic social challenge. In this study, male CD-1 mice (n = 14) were implanted with a radiotelemetry system for electrocardiographic recordings. We assessed the effects of chronic psychosocial stress (15-day sensory contact with a dominant animal and daily 5-min defeat episodes) on 1) sympathovagal responsiveness to each defeat episode, as measured via time-domain indexes of heart rate variability (R-R interval, standard deviation of R-R interval, and root mean square of successive R-R interval differences), 2) circadian rhythmicity of heart rate across the chronic challenge (night phase, day phase, and rhythm amplitude values), and 3) amount of myocardial structural damage (volume fraction, density, and extension of fibrosis). This study indicated that there was habituation of acute cardiac autonomic responsiveness, i.e., the shift of sympathovagal balance toward sympathetic dominance was significantly reduced across repeated defeat episodes. Moreover, animals exhibited significant changes in heart rate rhythmicity, i.e., increments in day and night values and reductions in the rhythm amplitude, but these were limited to the first 5 days of chronic psychosocial stress. The volume fraction of fibrosis was sixfold larger than in control animals, because of the appearance of many microscopic scarrings. In summary, although mice appeared to adapt to chronic psychosocial stress in terms of acute cardiovascular responsiveness and heart rate rhythmicity, structural alterations occurred at the myocardial level.

Aging and the endothelium

One link between aging and endothelial function is the inflammatory response. On one hand, the latter shortens the biological engaged by activated leukocytes against invaders or stressing agents. On the other hand, the surveyed tissues become targets of the toxicity of reactive oxygen species, ROS. The ensuing regeneration is source of transcriptional infidelity, leading to the alteration of the repaired tissue. Hence, the toll of inflammatory stress consists in premature senescence of cell and tissues. This hypothesis is discussed in the present review, which focuses on the molecular targets relevant for cancer and degenerative diseases, both tributary to an inflammatory environment and taking advantage from the consequences of cell and tissue dysfunctions characteristic of aging. Eventually, adaptation to stress, whatever its origin -inflammatory and/or psychosocial-is discussed. Basal nitric oxide (NO) release, such as provided through moderate exercise, seems to be the most potent guardian against immune, nervous and cardiovascular over-stimulation. Tissue regeneration is also obtained by circulating endothelial progenitors able to recognize the damaged tissue. To avoid post-inflammatory alterations resulting in detrimental changes of tissues and organs, the pharmacological protection of endothelium by agents able to modulate its activation seems crucial to us.

Ovarian Dysfunction, Stress, and Disease: A Primate Continuum

Menopause is recognized as a period of increased risk for coronary heart disease (CHD) and osteoporosis. Vulnerability to these conditions is often attributed to the naturally occurring estrogen deficiency characteristic of this part of the life cycle. Premenopausal reductions in endogenous estrogen occasioned by functional ovarian abnormalities or failure are hypothesized to be similarly pathogenic and to accelerate development of CHD and osteoporosis prematurely, thereby increasing the health burden of older women. These functional abnormalities, which occur along a continuum from mild, luteal phase progesterone deficiency to amenorrhea, are relatively common and are often attributed to psychogenic factors (stress, anxiety, depression, or other emotional disturbance), exercise, or energy imbalance. Although numerous investigators have commented on these functional deficits, the abnormalities can be difficult to diagnose and are generally unappreciated for the contribution they may make to postmenopausal disease. Studies in nonhuman primates confirm that these deficits are easily induced by psychological stress and exercise, and that they accelerate the development of cardiovascular disease and perhaps bone loss in the presence of a typical North American diet. However, functional reproductive deficits are also reversible and are thus potentially amenable to environmental or behavioral intervention. Data from both women and nonhuman primates support the hypothesis that functional reproductive deficits are adaptive when triggered appropriately but are detrimental when activated in an environment (e.g., sedentary lifestyle, high-fat diet) permissive to the development of chronic disease.

Antiatherosclerotic effects of beta-blockers

Accumulating data from studies in animals and humans indicate that beta-blockade has antiatherosclerotic effects. To date, 2 long-term ultrasound studies provide the strongest evidence. The Beta-Blocker Cholesterol-Lowering Asymptomatic Plaque Study (BCAPS) trial reported favorable effects with beta-blockade on early stages of atherosclerosis in patients with carotid plaque but no symptoms of carotid artery disease. Compared with placebo, metoprolol controlled release/extended release (CR/XL) 25 mg once daily significantly reduced plaque thickness after 18 months of treatment (net difference -0.058 mm/year; p <0.001) and at 3 years' follow-up (net difference -0.023 mm/year; p = 0.018). The Effects of Long-Term Treatment of Metoprolol CR/XL on Surrogate Variables for Atherosclerotic Disease (ELVA) trial demonstrated that beta-blockers and statins affect different mechanisms in the atherosclerotic process and have additive beneficial effects. Patients with hypercholesterolemia were randomized to metoprolol CR/XL 100 mg once daily or placebo once daily and concomitant statin therapy. The metoprolol CR/XL group had a significantly lower rate of progression of the composite carotid bulb intima-media thickness (IMT) plus common carotid IMT than the placebo group, both at 1 year (-0.08 vs -0.01 mm; p = 0.004) and after 3 years' follow-up (-0.06 vs +0.03 mm; p = 0.011). Several factors may contribute to the mechanism of benefit in these trials, including reduced sympathetic activity, improved hemodynamic parameters, and direct effects on the vascular endothelium.

Consuming research, producing policy?

The authors' 1990 article "Producing Health, Consuming Health Care" presented a conceptual framework for synthesizing a rapidly growing body of findings on the nonmedical determinants of health. The article received a very positive response, and here the authors reflect on what lessons might be learned from that response about the style or content of effective interdisciplinary communication. Much substantive knowledge has been accumulated since 1990, and a number of different frameworks have been developed before and since. The authors situate theirs within this literature and consider how they might have modified it if they "knew then what they know now." They ask what impact this article, and the much broader stream of research on the determinants of health, has had on public policy?

Subjective social status: its determinants and its association with measures of ill-health in the Whitehall II study

The purpose of this study was twofold-(1) investigate the role of subjective social status as a predictor of ill-health, with a further exploration of the extent to which this relationship could be accounted for by conventional measures of socioeconomic position; (2) examine the determinants of a relatively new measure of subjective social status used in this study. A 10 rung self-anchoring scale was used to measure subjective social status in the Whitehall II study, a prospective cohort study of London-based civil service employees. Results indicate that subjective status is a strong predictor of ill-health, and that education, occupation and income do not explain this relationship fully for all the health measures examined. The results provide further support for the multidimensional nature of both social inequality and health. Multiple regression shows subjective status to be determined by occupational position, education, household income, satisfaction with standard of living, and feeling of financial security regarding the future. The results suggest that subjective social status reflects the cognitive averaging of standard markers of socioeconomic situation and is free of psychological biases.

Toward a causal model of cardiovascular responses to stress and the development of cardiovascular disease

OBJECTIVE

Cardiovascular reactivity is hypothesized to mediate the relationship between stress and cardiovascular disease. We describe three considerations that are crucial for a causal model of cardiovascular responses to stress: the need for laboratory-life generalizability, the role of interactions between environmental exposures and individual response predispositions, and the importance of the duration of both stressor exposure and cardiovascular responding.

METHODS

We illustrate current understanding of stress-cardiovascular disease relationships with examples from the human and animal psychophysiology, epidemiology, and genetics literature.

RESULTS

In a causal model of reactivity, the usefulness of laboratory assessment rests on the assumption that laboratory-based cardiovascular reactivity predicts responses in the natural environment. We find only limited generalizability and suggest that cardiovascular responses to stress can be better understood when examined in the natural environment. The interaction of individual response predispositions and stressor exposures contributes to the development and progression of cardiovascular disease; stress-disease relationships could therefore be better understood if predispositions and exposures were assessed simultaneously in interactive models. Cardiovascular responses to stress are likely to be most deleterious when responses are prolonged. Responses may vary in their magnitude, frequency, and duration; however, reactivity captures only response magnitude. The assessment of anticipatory and recovery measures, with response magnitude, may therefore lead to a more useful model of the stress-disease relationship.

CONCLUSIONS

A causal model of cardiovascular responses to stress should generalize to the real world, assess interactions between individual predispositions and environmental exposures, and focus on sustained pathogenic exposures and responses.

Effects of psychological and social factors on organic disease: a critical assessment of research on coronary heart disease

An extensive research literature in the behavioral sciences and medicine suggests that psychological and social factors may play a direct role in organic coronary artery disease (CAD) pathology. However, many in the medical and scientific community regard this evidence with skepticism. This chapter critically examines research on the impact of psychological and psychosocial factors on the development and outcome of coronary heart disease, with particular emphasis on studies employing verifiable outcomes of CAD morbidity or mortality. Five key variables identified as possible psychosocial risk factors for CAD are addressed: acute and chronic stress, hostility, depression, social support, and socioeconomic status. Evidence regarding the efficacy of psychosocial interventions is also presented. It is suggested that, taken as a whole, evidence for a psychological and social impact on CAD morbidity and mortality is convincing. However, continued progress in this area requires multidisciplinary research integrating expertise in cardiology and the behavioral sciences, and more effective efforts to communicate research findings to a biomedical audience.

Rat sex and strain differences in responses to stress

Sensitivity to stress has been linked to the development of a variety of physical and psychological disorders. Studies to-date have focused on extreme stress phenotypes, have studied mostly male responses, have used limited dependent variables, and have included a limited number of measurement time points. The present experiment was designed to address these limitations. Feeding, body weight, open-field activity, acoustic startle reflex (ASR), and prepulse inhibition (PPI) responses of adult male and female Sprague-Dawley and Long-Evans rats to daily immobilization stress (20 min/day) were evaluated for 3 weeks. Stress significantly decreased feeding and body weight of males but generally not of females. Effects were greatest in Long-Evans males. Stress decreased 15-min activity levels for males on Stress Day 1, but not on other days. Stress did not affect 15-min activity levels of Long-Evans females but decreased 15-min activity levels of Sprague-Dawley females on every measurement day. ASR responses to stress differed based on rat strain; percent PPI responses differed based on rat strain and sex. Stress increased startle responses of Sprague-Dawley males and females but not of Long-Evans males and females. Stress reduced PPI of Long-Evans females on every measurement day but not of other groups. These findings indicate that strain and sex of rat is important to consider in evaluating behavioral and physiological responses to stress.

Effect of controlled release/extended release metoprolol on carotid intima-media thickness in patients with hypercholesterolemia: a 3-year randomized study

BACKGROUND AND PURPOSE

Beta-adrenergic blockade has in several studies been shown to improve survival after myocardial infarction. In animal experiments beta-blockers have also shown an antiatherosclerotic effect. The aim of this study was to test the hypothesis that the beta-blocker metoprolol succinate controlled release/extended release (CR/XL), when given to patients with hypercholesterolemia on concomitant lipid-lowering therapy, provides an additional antiatherosclerotic effect to that provided by the statins, measured as carotid intima-media thickness (IMT).

METHODS

We conducted a randomized, double-blind, placebo-controlled, single center trial to compare the effect of metoprolol CR/XL (100 mg once daily) and placebo on the progression of carotid IMT during 36 months of treatment in patients with hypercholesterolemia and signs of early atherosclerosis in the carotid artery. Most patients were prescribed lipid-lowering treatment with statins.

RESULTS

A highly significant difference in the progression rate of the composite variable of carotid bulb IMT+common carotid IMT was observed between the metoprolol CR/XL and placebo groups after 1 year of treatment (-0.08 versus -0.01 mm; P=0.004), an effect that was sustained after 3 years of follow-up (-0.06 versus +0.03 mm; P=0.011). The patients had high levels of total cholesterol at randomization: 9.4 mmol/L in the metoprolol CR/XL group and 8.6 mmol/L in the placebo group. During the study the 2 randomization groups were treated with lipid-lowering drugs, mainly statins, to a similar extent, and total cholesterol was reduced to 6.4 mmol/L at end of follow-up in both groups.

CONCLUSIONS

The results from the present study in patients with hypercholesterolemia under concomitant lipid-lowering therapy are the first clinical data to show an antiatherosclerotic effect of beta-blockade as additional therapy to statins. The data indicate that statin treatment and treatment with beta-blockers affect different mechanisms in the atherosclerotic process and have additive beneficial effects.

Predictors of social status in cynomolgus monkeys (Macaca fascicularis) after group formation

The purpose of the present study was to determine whether various behavioral and hormonal markers obtained in individually housed monkeys would be predictive of social rank following group housing. Body weight, serum cortisol and testosterone levels, and locomotor activity in an open-field apparatus were examined in 20 experimentally naive male cynomolgus monkeys (Macaca fascicularis) while they were individually housed. It was hypothesized that eventual subordinate monkeys would have higher cortisol levels and increased locomotor activity scores. These monkeys were then placed in social groups of four (five pens of four monkeys), and social rank was determined based on outcomes of dyadic agonistic encounters. Body weight correlated significantly with eventual social rank. In general, the heavier the monkey the higher the social rank. Locomotor activity in an open-field apparatus following administration of a low dose of cocaine (0.01 mg/kg, i.v.), which has been shown to increase CNS dopamine, correlated with eventual social rank such that individually housed monkeys with high levels of locomotion were more likely to become subordinate. Serum cortisol and testosterone levels failed to correlate with eventual social rank. Hypothalamic-pituitary feedback sensitivity and adrenal responsiveness were examined by measuring cortisol levels after administration of dexamethasone and following ACTH challenge. Cortisol responses in these tests were not associated with eventual social rank. These results suggest that, in addition to body weight, the level of reactivity in a novel environment after administration of a low dose of cocaine is a potential trait marker for social rank. This trait is apparently not associated with hormone levels, but may involve other CNS mechanisms.

Socioeconomic status and health: what we know and what we don't

In the past 15 years, we have seen a marked increase in research on socioeconomic status (SES) and health. Research in the first part of this era examined the nature of the relationship of SES and health, revealing a graded association; SES is important to health not only for those in poverty, but at all levels of SES. On average, the more advantaged individuals are, the better their health. In this paper we examine the data regarding the SES-health gradient, addressing causal direction, generalizability across populations and diseases, and associations with health for different indicators of SES. In the most recent era, researchers are increasingly exploring the mechanisms by which SES exerts an influence on health. There are multiple pathways by which SES determines health; a comprehensive analysis must include macroeconomic contexts and social factors as well as more immediate social environments, individual psychological and behavioral factors, and biological predispositions and processes.

Social status and susceptibility to respiratory infections

Adults and children of lower socioeconomic status (SES) are at higher risk for a wide range of communicable infectious diseases, especially respiratory infections. Greater risk for infectious illness among people with lower SES is thought to be attributable to increased exposure to infectious agents and decreased host resistance to infection. We summarize three studies that examine the prospective association of several markers of social status (unemployment, perceived and observed social status) with host resistance to upper respiratory infections. Unemployment was associated with increased susceptibility to infection in adult humans. Lower social status in male monkeys was also associated with increased susceptibility, as was lower perceived social status in humans. The association of social status and susceptibility was accounted for primarily by increased risk in the lowest social status groups. However, further increases in social status were associated with further decreases in susceptibility in both monkeys and humans.