Chronic effects of high salt intake and conflict stress on blood pressure in primates. A progress report.

The effects of combined behavioral stress and high dietary salt on blood pressure were examined in baboons (N = 4) over the course of 1 year. Either high salt diet (240 mEq Na+/day) or conflict stress were administered for 8 to 16 weeks, followed by high salt intake and stress combined. Mean arterial pressure (MAP) increased by 8 mmHg during high dietary salt alone, by 4 mmHg during stress alone, and increased further to 14 mmHg above baseline during combined salt and stress. Control baboons (N = 2) had no change in MAP across 47 weeks. The data indicate additive effects of chronic high dietary salt intake and behavioral stress on blood pressure in non-human primates.     

Chronic effects of high salt intake and conflict stress on blood pressure in primates

The effects of combined behavioral stress and high dietary salt on blood pressure were examined in baboons (N=4) over the course of 1 year. Either high salt diet (240 mEq Na⁺/day) or conflict stress were administered for 8 to 16 weeks, followed by high salt intake and stress combined. Mean arterial pressure (MAP) increased by 8 mmHg during high dietary salt alone, by 4 mmHg during stress alone, and increased further to 14 mmHg above baseline during combined salt and stress. Control baboons (N=2) had no change in MAP across 47 weeks. The data indicate additive effects of chronic high dietary salt intake and behavioral stress on blood pressure in non-human primates.     

Blood pressure hyperreactivity in non-human primates during dietary sodium combined with behavioral stress

The potential for behavioral stress alone or combined with dietary salt to augment pressor reactivity to the onset of daily experimental sessions was examined in normotensive, intact baboons over the course of four months. During twice daily experimental sessions, adult male baboons experienced food/shock conflict such that lever pulling not only served to earn food, but was also occasionally punished with cued mild electric shock. Blood pressure and heart rate were measured during a baseline period of fixed-ratio food reinforcement (3 weeks), during conflict stress (2 weeks), and after dietary salt was added to the daily conflict protocol (CONFLICT + SODIUM, 3 weeks). Reactivity, i.e., acute changes in blood pressure and heart rate to the daily experimental sessions, was not evident during food reinforcement sessions nor during the CONFLICT stress alone condition. The addition of a high salt diet virtually doubled blood pressure increases and heart rate decreases to the onset of experimental sessions. Average reactivities during CONFLICT + SODIUM periods were 11.2/7.9% delta for SBP/DBP (systolic/diastolic blood pressure, mmHg), and -5.65% delta for HR (heart rate, BPM). Neither atenolol nor hydrochlorothiazide diuretic significantly altered cardiovascular reactivity during CONFLICT + SODIUM in comparison to a preceding non-drug CONFLICT + SODIUM period. When atenolol and diuretic effects were directly compared, atenolol mildly augmented, while diuretic mildly decreased DBP but not SBP reactivity during CONFLICT + SODIUM. Reactivity was eliminated after salt loading and behavioral sessions were terminated. These findings provide evidence that enhanced salt ingestion may synergistically act with behavioral stress to produce pressor hyperresponsiveness to otherwise benign environmental events.     

Potassium supplementation induces beneficial cardiovascular changes during rest and stress in salt sensitive individuals.

The typical American diet includes high salt and low potassium, a pattern linked to elevated blood pressure (BP) in cross-cultural studies. This study compared resting and stress cardiovascular responses on a high salt, low potassium diet to those observed during 2 interventions: salt restriction and potassium supplementation. Forty-seven percent of the primarily normotensive sample (n = 67 adults) were salt sensitive, showing a decrease in mean arterial pressure > or = 5 mmHg during low salt and equivalent reductions during high potassium. The equivalent benefits of the interventions were maintained, but not enhanced, during exposure to behavioral stress (i.e., no effect on reactivity). Salt resistants (SRs) exhibited no change in resting or stress BP across the diets. High salt increased cardiac index in both groups, whereas vascular tone was decreased only in the SR group. High potassium produced hemodynamic benefits similar to low salt, even with continued high salt intake.     

Effects of a high salt diet on blood pressure responses to acoustic stimuli in borderline hypertensive rats (BHR)

The borderline hypertensive rat (BHR) responds to environmental and dietary stressors with elevated blood pressure. The first two months of a high salt diet appear to be the time of greatest sensitivity to salt effects on the blood pressure of BHR. The current study was conducted to examine whether exposure to salt diets varying in duration for up to two months differentially affects baseline blood pressures (systolic, SBP, and diastolic, DBP) and blood pressure responses to novel acoustic stimuli in BHR and normotensive Wistar-Kyoto (WKY) rats. Male BHR and WKY were fed a control (1%) salt diet or a high (8%) salt diet for 1, 1.5, 2.5, or 8.5 weeks. SBP and DBP responses to an acoustic stimulus (85 dB, 3 kHz) were measured upon completion of the diets at 12 weeks of age. Ten acoustic trials (one stimulus/minute) were presented and blood pressure responses were recorded in 2-second blocks spanning the 10 seconds prior to and following stimulus presentation. BHR had higher resting SBP and DBP than WKY, and 8.5 weeks of 8 percent salt increased SBP markedly in BHR. SBP and DBP labilities in the initial trial were greater in BHR than WKY with high salt diet durations of 2.5 and 8.5 weeks producing greater lability in later trials. Few differences were noted in pressor responses, but BHR had more dramatic depressor responses than WKY in early trials, and BHR pressures had a more dramatic return to baseline. It appears that genetic history and salt diet can affect blood pressure lability and recovery in response to novel stimuli in genetically susceptible animals.     

Lipid reactivity to stress: II. Biological and behavioral influences.

This study examined behavioral and physiological influences on lipid concentrations during acute and chronic stressors. One hundred men (n = 92) and women (n = 8) were tested during a chronic stressor and during 2 acute stressors. During chronic stress, diet, physical activity, exercise, and sleep were examined. During the acute stressors, catecholamines, cortisol, plasma volume, and cardiovascular responses were examined. None of the behavioral influences could explain the lipid response to chronic stress. Responses of the atherogenic lipids to acute stressors were not solely reflecting hemoconcentration of the plasma but were moderately correlated with cardiovascular, epinephrine, and cortisol reactivity. Diastolic blood pressure reactors to the acute stressors had larger lipid responses to the chronic stressor than did nonreactors. Elevations in blood lipids during stress are not artifacts and may be clinically significant.     

Open-field behavior in two models of genetic hypertension and the behavioral effects of salt excess

In order to assess the relationship of behavior to blood pressure and salt intake, open-field behavior was studied in 123 rats of the spontaneously hypertensive (SHR), Wistar-Kyoto (WKY), Sprague-Dawley (SD), and Dahl resistant (DR) and sensitive (DS) strains. DS rats become hypertensive upon exposure to either high dietary salt or psychogenic stress, while DR rats remain normotensive. A circular photobeam open field was used under full room illumination. Three 5-min trials were given on consecutive days. Rats were tested with or without 5 days of an 8% NaCl diet. We found that DS rats were less active than DR rats, regardless of diet. In contrast, SHR rats were more active than WKY rats. However, DS and SHR rats were equally active. Thus, behavioral differences between these two models of hypertension are expressed by the normotensive control strains. The relative ranking of activity levels between strains was DR = SD greater than SHR = DS greater than WKY. High-salt-enhanced intertrial habituation, defined as the decrease in activity across trials (DS, 100%; SD, 82%; SHR, 90%; WKY, 1350%; but DR, -50%) as well as intratrial habituation, defined as the decrease from the first to the second half of the trial (14%, all subjects). Defecation was increased with high salt (DS, 975%; SD, 59%; SHR, 267%; WKY, 89%; but DR, 40%). These effects of high salt may reflect an increase in an emotionality factor. DR rats were largely resistant to the behavioral effects of salt. Total activity was positively correlated with blood pressure in hypertensive rats, r(42) = 0.33, p less than .01, but negatively correlated in normotensive rats, r(81) = -0.34, p less than .01. The proportion of total activity occurring in the first half of the trial for the initial test day was correlated with blood pressure in normotensive rats r(81) = 0.44, p less than .01. Dietary salt excess has behavioral as well as cardiovascular consequences.     

Behavioral performance effects of verapamil in normotensive and renovascular hypertensive baboons.

Behavioral performances of normotensive and hypertensive adult male baboons were tested before, during, and following chronic oral dosing with verapamil. Performances during a five-color simultaneous match-to-sample task were measured for two doses (2.0, and 3.2 mg/kg/day) and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Choice reaction times increased by 9% during the lower dose of verapamil, compared to vehicle; choice reaction times were unchanged at the higher dose. At baseline and during vehicle administration, the yellow and white stimuli were the most difficult to discriminate correctly; discrimination of these colors was slightly impaired by the lower, but not the higher dose of verapamil. Verapamil's behavioral effects were not modulated by blood pressure changes since both baboon groups showed equivalent changes in behavioral performance, but only renovascular hypertensive baboons showed blood pressure decreases. Verapamil appears to be an effective hypotensive and does not produce profound psychomotor impairment at clinically used doses during the first weeks of treatment.     

Behavioral performance effects of verapamil in normotensive and renovascular hypertensive baboons

Behavioral performances of normotensive and hypertensive adult male baboons were tested before, during, and following chronic oral dosing with verapamil. Performances during a five-color simultaneous match-to-sample task were measured for two doses (2.0, and 3.2 mg/kg/day) and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Choice reaction times increased by 9% during the lower dose of verapamil, compared to vehicle; choice reaction times were unchanged at the higher dose. At baseline and during vehicle administration, the yellow and white stimuli were the most difficult to discriminate correctly; discrimination of these colors was slightly impaired by the lower, but not the higher dose of verapamil. Verapamil’s behavioral effects were not modulated by blood pressure changes since both baboon groups showed equivalent changes in behavioral performance, but only renovascular hypertensive baboons showed blood pressure decreases. Verapamil appears to be an effective hypotensive and does not produce profound psychomotor impairment at clinically used doses during the first weeks of treatment.     

Predictability of chronic intermittent stress: effects on sympathetic-adrenal medullary responses of laboratory rats

This experiment involved an examination of sympathetic-adrenal medullary responses of laboratory rats following exposure to chronic intermittent stress. Animals were assigned at random to one of three groups: (i) controls, handled briefly each day; (ii) restraint stress (RS), restrained for 30 min per day; or (iii) variable stress (VS), exposure to restraint, cold swim, or intermittent footshock during one of five time periods each day. On the 26th day, rats were prepared with chronic tail artery catheters for remote sampling of blood and direct measurement of mean arterial pressure and heart rate. On Day 28, rats of each group were exposed to 30 min of restraint stress and timed blood samples were collected and later analyzed for content of norepinephrine (NE) and epinephrine (EPI). VS rats gained significantly less body weight compared to control and RS rats. Basal measures of blood pressure and heart rate and of plasma NE and EPI were comparable for rats of the three groups. The plasma catecholamine responses to restraint stress on Day 28 were significantly reduced in RS and VS rats compared to first-time stressed controls. These findings suggest that predictability of the type of stressor and the time of its occurrence does not influence the pattern of diminished sympathetic-adrenal medullary responses of animals exposed to chronic intermittent stress.     

Long-term effects of footshock and social defeat on anxiety-like behaviours in rats: Relationships to pre-stressor plasma corticosterone concentration

We compared the consequences of two stressors, 'unnatural' inescapable footshocks (IFSs) and 'natural' social defeat (SD), on behaviours typically sensitive to stress [sucrose preference, open field (OF), elevated plus maze (EPM) and acoustic startle responses (ASRs)] and the association with pre-stressor plasma corticosterone concentration. After initial blood sampling, rats (n?=?20 per group) were exposed to either 10 IFSs (1?mA intensity, 5?s duration each) or to 1?h SD (defeat by an aggressive resident male rat and further exposure but separated in a small cage) or to control procedures (handling). Rats were tested once for ASR (day 19), while the other behavioural tests were applied once weekly for 3 weeks. Both stress groups showed short-lasting lowered sucrose preference, and in the EPM they showed shorter total distance moved, shorter distance moved on open arms and less time on open arms compared to controls. In the OF test, IFS rats showed shorter total distance moved up to 2 weeks after stress. The SD group showed shorter total distance moved in the OF, which was only significant 2 weeks after stress. Low pre-stressor plasma corticosterone concentration was only associated with defecation (IFS rats) and latency to enter open arms in the EPM (all low corticosterone subgroups, n?=?10 per subgroup). SD rats with high initial plasma corticosterone concentration showed enhanced ASR compared to the other subgroups with high initial plasma corticosterone concentration (n?=?9 per subgroup). The results indicate that footshock and SD, while generally leading to an increase in anxiety behaviours, represent qualitatively different stressors.     

Perceived stress and diabetes control in adolescents

Studies of diabetes control have traditionally focused on patients' regulation of insulin, diet, and exercise. Although psychosocial stress may also influence blood glucose, researchers have infrequently accounted for the three primary physiological factors when estimating the effects of stress. In addition, few investigators have considered the influence of everyday minor stressors on health outcome. The Tennessee Camp for Diabetic Children provided an opportunity to monitor insulin administration, dietary intake, and exercise levels and to obtain measures of blood glucose and perceived minor stressors. The best index of stress was one in which number and magnitude of negative stressors were combined into a cumulative stress measure. Negative cumulative stress significantly correlated with blood glucose levels after controlling for the effects of insulin, diet, and exercise. In addition, diabetes control tended to be better when adolescents, particularly boys, adjusted well to negative stress. These findings suggest that minor stressors can influence health outcome, but positive and negative stress need to be assessed independently.     

Clergy Role Stress and Satisfaction: Role Ambiguity Isn’t Always Bad

This study examined relationships between role conflict and role ambiguity and clergy satisfaction with their church appointment. Questionnaire data obtained from 293 United Methodist clergy suggested that role conflict and role ambiguity each have a negative relationship with appointment satisfaction. However, when considered together, they displayed a more complex relationship with appointment satisfaction. Contrary to conventional wisdom, results indicated that although these stressors operate together to influence appointment satisfaction, their combined effect is not simply cumulative. That is, when role conflict is low, clergy report the most satisfaction when role ambiguity is high. However, when role conflict and role ambiguity are both high, appointment satisfaction is low. These findings are interpreted in light of clergy influence strategies. And, recommendations for remedying clergy role stress are offered. Furthermore, it is suggested that interactive models of role stressors could lead to more in-depth understanding of organizational stress as well as advances in role stress theory.     

Chronic stress influences cardiovascular and neuroendocrine responses during acute stress and recovery, especially in men.

This study tests the influence of chronic stress on cardiovascular and neuroendocrine responses to and recovery from acute stressors and whether the effects are gender specific. Sixty-two healthy, middle-aged persons (50% women) performed mental-arithmetic and public-speaking tasks and relaxed thereafter for 1 hr while their cardiovascular and neuroendocrine function was measured. Participants with higher levels of chronic stress showed lower systolic blood pressure (SBP) and epinephrine (E; men only) and marginally lower levels of norepinephrine (NE) responses to the tasks and showed lower levels of cortisol and marginally lower NE responses during recovery. Relative to women, men had high diastolic blood pressure (DBP) responses to the tasks and high SBP, DBP, and E responses during recovery. Gender differences in cardiovascular disease in midlife may be due to gender differences in the inability to recover quickly, in addition to enhanced acute-stress response.     

The effects of racial stressors and hostility on cardiovascular reactivity in African American and Caucasian men.

This study examined the effects of race-related stressors and hostility on cardiovascular reactivity in 31 African American and 31 Caucasian men. Participants viewed 3 film excerpts that depicted neutral, anger-provoking (but race-neutral), and racist situations. Participants exhibited significantly greater diastolic blood pressure reactivity to anger-provoking and racist stimuli compared with neutral stimuli. In addition, high hostility was associated with higher recovery systolic and diastolic blood pressure levels after exposure to the films. Although the results failed to confirm previous reports of greater reactivity to racism in African Americans, the findings suggest that diastolic blood pressure levels may remain elevated after exposure to racist stimuli. These results indicate that even indirect exposure to interpersonal conflict elicits significant reactivity, which can persist after exposure to the stressor, especially among high-hostile men.     

Toward an understanding of psychological burnout among police officers

This study examined a research model developed to understand psychological burnout among police officers. Data were collected from 828 men and women in police work using questionnaires completed anonymously. Five groups of predictor variables identified in previous research were considered: individual demographic and situational variables, work stressors, stressful events, work-family conflict and coping responses. Sources of stress (chronic stressors, stressful events, work-family conflict) were significantly related to levels of psychological burnout when individual demographic and situational variables were controlled.     

Cardiovascular reactivity and neuroticism: results from a laboratory and controlled ambulatory stress protocol

A laboratory and controlled ambulatory protocol was used to study whether there are differences in the cardiovascular reactivity of persons varying in neuroticism, the disposition to experience negative subjective emotions. Thirty-six individuals (19 men, 17 women) who scored approximately 1 standard deviation above or below the mean on the NEO PI-R Neuroticism scale (Costa & McCrae, 1992) were recruited from a larger pool of undergraduate students. Participants, who had been outfitted with an ambulatory blood pressure/heart rate monitor, were exposed to 5 laboratory stressors and 7 field stressors during a 6-hour protocol. Results indicated that individuals scoring high in neuroticism showed blood pressure reactivity to laboratory and field stressors that was comparable to that of persons low in neuroticism. Aggregrating responses across stressors, there was evidence of exaggerated heart rate responses. The results suggested that, although neuroticism is related to high levels of negative subjective experience, differences between persons scoring high versus low in neuroticism were not exhibited strongly at the cardiovascular level. The implications for stress, coping, and disease are discussed.     

Does anxiety or cardiovascular reactivity have a causal role in hypertension?

Anxiety, stress, and cardiovascular reactivity (CVR) are variously believed to play a role in sustained hypertension. Although acute anxiety or stress elicits acute pressor responses, there is little support for their significant role in sustained hypertension. Anxiety correlates poorly with CVR, and blood pressure levels and anxiolytics do not sustain blood pressure lowering in subjects with hypertension-associated anxiety. Chronic anxiety disorders tend to be characterized by relatively low blood pressure and prevalence of sustained hypertension. Blood Pressure Regulation in hypertension is normal, and normo- and hypertensives have similar ambulatory blood pressure variability. Laboratory CVR fails to predict variability in natural environments, hyperreactors do not exhibit increased variability in natural environments, and the increased variability and ambulatory reactivity that is "accounted for" by laboratory responses is small. These findings do not support the belief that hypertension is related to a summation of heightened pressor responses over time. Antihypertensives normalize elevated blood pressures but do not alter CVR in the laboratory or variability in natural environments, probably because of a dual central regulation of resting and reactive blood pressures. Psychological stress responses result from selective neuronal activation rather than from generalized sympathetic neural responses or dysregulation. Differences in blood pressure responses during various emotions are only quantitative, with no specificity of sympathoadrenal or emotional responses to stressors. It may be time to regard reactive cardiovascular responses as physiological, rather than as psychological, and to require much stronger evidence to confirm causal roles of anxiety, stress, and reactivity in sustained hypertension.     

Effects of social defeat on acute cardiovascular response in salt-sensitive and salt-resistant rats

We studied the effects of social stress (SS) and a high salt diet on systolic blood pressure (SBP) and heart rate (HR): S/JR male rats (which exhibit marked elevations in SBP when placed on a high sodium diet) and R/JR male rats (which are resistant to the BP-elevating effects of a high sodium diet) were maintained on a low sodium diet (0.3% NaCl) or placed on a high sodium diet (8% NaCl). Within each dietary condition independent groups were either exposed to SS, by placement in the cage of a trained fighter male (Long-Evans breed) for 25 min, or exposed to no stress. The dietary regimen was imposed for 10 days with stress exposures on Days 1, 2, 3, 5, 7, and 9, with SBP and HR measured indirectly by tail plethysmography 3 min following exposure to SS. SS produced an acute decrease in SBP (20-30 mm Hg) in S/JR rats on the second and subsequent exposures, but did not affect HR. SS did not affect SBP of R/JR rats, but did produce a significant elevation of HR. Maintenance on the high sodium diet increased SBP in S/JR, but not R/JR, rats when it was measured on the eighth (no stress) day, but SS obscured the effects of diet on SBP on days when rats were stressed. Following exposure to attacks, defeated SS rats displayed an upright submissive posture relatively late during the first stress exposure when no change in SBP was observed after SS in S/JRs, but displayed the submissive posture immediately and with long duration on the second and subsequent exposures when a marked decrement in SBP was seen.     

Lipid reactivity to stress: I. Comparison of chronic and acute stress responses in middle-aged airline pilots.

Lipids increase during psychological stress, but no studies have compared the effects of acute and chronic stressors on lipid responsivity in the same individuals. One hundred middle-aged men (n = 92) and women (n = 8) were examined during high chronic occupational stress, low chronic stress, and acute laboratory stressors. In addition to measures of perceived stress and affect, an extensive battery of lipid and lipoprotein measures was undertaken at each time point. Most lipid parameters were significantly increased during the chronic and acute stressors, although the responses to the different stressors were not consistently associated. For example, significant correlations among the chronic and acute stress responses were apparent for the apoproteins, but not for total, low density lipoprotein, or high density lipoprotein cholesterol. The factors and processes regulating these variables during stress may be different during acute and chronic stressors.