The spontaneously hypertensive rat (SHR) is an excellent model of essential hypertensive disease. Hyperreactivity has been postulated as a contributing factor in the development of high blood pressure in the SHR and in man. In the maturing organism recurring hypertensive stesss responses may promote permanent vascular changes and result in a fixed hypertension. Simple behavioral activity and emotionality rating scales were used to compare a large number of SHR with equally large groups of closely-related and distantly-related normotensive rats. As predicted, the SHR were clearly more active and emotional than their ancestral Wistar Kyoto (WKY) strain. However, the distantly-related normotensive Wistars did not differ from the SHR in either activity or emotionality. These results indicate that behavior and hypertension are not necessarily related in the rat. Nonetheless, the behavioral differences between the SHR and their closest genetic match, the WKY, suggest that arousal and blood pressure levels may be causally linked in this case of naturally occurring hypertension.

Animals↗

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Lifelong hyperarousal in the spontaneously hypertensive rat indicated by operant behavior.

Instrumental conditioning techniques were used to obtain objective evidence of differences in behavioral arousal between the spontaneously hypertensive rat (SHR) and the normotensive ancestral Wistar Kyoto (WKY) strain. Subjective emotionality ratings previously indicated that the genetically hypertensive rats were more active and aggressive than their normotensive cousins. In a lengthy series of operant conditioning sessions using a small number of adult female SHR and WKY rats, hyperarousal in the SHR was confirmed by their significantly higher response outputs on either response contingent or time contingent schedules of reinforcement. Conditioned emotionality tests during this series of experiments also suggested hyperarousal and aggressiveness in the SHR, since the fear-conditioned stimulus suppressed bar-pressing in the SHR much less than in the WKY. Further experiments with young prehypertensive SHR rats provided the same evidence of hyperresponsivity in the SHR compared to the WKY strain. Furthermore, these young SHR failed to develop hypertension by the end of the study (14 weeks of age), while their nonconditioned SHR cousins had become clearly hypertensive by the same age. This suggests that factors related to the conditioning methods modified the development of high blood pressure in this animal model of essential hypertension.

Age Factors↗

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Water deprivation associated with operant conditioning inhibits hypertensive disease in young spontaneously hypertensive rats.

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Animals↗

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Nutritional assessment of protein status.

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Anthropometry↗

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Work pressure and the type A behavior pattern exam stress in male medical students.

The psychologic and physiologic effects of variations in occupational stress on Type A (coronary-prone) and Type B men have not previously been examined. Accordingly, 58 male medical students in two successive first-year classes (32 As, 26 Bs defined by interview) were tested for mood states, perception of work pressure, and for pituitary-adrenal and cardiovascular function during a period of minimal work pressure (no exams for 1 week) and during maximal work pressure (final exam week). All observations were made at the beginning of the school day, while the students were studying course material in the building where classes were held and study modules were located. Perceived stress and self-ratings of dysphoric moods increased significantly (ps less than 0.0005) for both groups during exams compared to no exams. Plasma cortisol concentrations increased significantly (+20%) from no exams to exams for both As and Bs. Heart rate increased significantly to exams (+8%) and did so slightly more for As (+9%) than for Bs (+7%), with As showing significantly higher rates in the work setting at both times. Systolic blood pressure increased nonsignificantly for both groups. The effect of the higher heart rate and the slight systolic blood pressure rise produced a significantly greater rate-pressure product for As than for Bs at both exams and no exams (p less than 0.005), with As showing a larger rise to exams than did Bs (+11% vs. +8%). Results indicate that the As had a higher level of tonic cardiovascular activation in the work place than the Bs, and that this was additive with the effects of increased work pressure.

Adult↗

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Mechanisms of myocardial ischemia induced by epinephrine: comparison with exercise-induced ischemia.

The role of epinephrine in eliciting myocardial ischemia was examined in patients with coronary artery disease. Objective signs of ischemia and factors increasing myocardial oxygen consumption were compared during epinephrine infusion and supine bicycle exercise. Both epinephrine and exercise produced myocardial ischemia as evidenced by ST segment depression and angina. However, the mechanisms of myocardial ischemia induced by epinephrine were significantly different from those of exercise. Exercise-induced myocardial ischemia was marked predominantly by increased heart rate and rate-pressure product with a minor contribution of end-diastolic volume, while epinephrine-induced ischemia was characterized by a marked increase in contractility and a less pronounced increase in heart rate and rate-pressure product. These findings indicate that ischemia produced by epinephrine, as may occur during states of emotional distress, has a mechanism distinct from that due to physical exertion.

Arousal↗

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Heart rate reactivity as a predictor of neuroendocrine responses to aversive and appetitive challenges.

The present paper examines the neuroendocrine influences of aversive and reward incentives (noise and shock versus monetary bonuses) presented during reaction time tasks administered to 71 healthy men (ages 21 to 35) classified as being high (N = 30) or low (N = 41) in heart rate reactivity. High heart rate reactivity was defined as a peak heart rate increase or greater than 19 bpm to a cold pressor test administered on a different day. Independent groups of subjects worked on one of two visual reaction time tasks: either to avoid exposure to noise (115-dBA bursts) and shock (3.5 mV, 2 sec), or to earn monetary bonuses ($0.50). High heart rate reactors showed significant plasma norepinephrine rises from baseline both to aversive incentives and to reward, although they showed significant cortisol responses only during aversive incentives. In contrast, the low heart rate reactors were unresponsive in cortisol and norepinephrine during either type of incentive. These results support psychoendocrine models which view the norepinephrine response as being nonspecifically related to expenditure of effort regardless of the emotional connotations of the challenge, while cortisol is seen as being secreted primarily during periods of distress. The present data further suggest that cardiovascular reactivity is linked to neuroendocrine reactivity, possibly within the central nervous system.

Adult↗

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Hypothalamic-pituitary-adrenocortical responses to psychological stress and caffeine in men at high and low risk for hypertension.

OBJECTIVE: This study examined pituitary-adrenocortical responses to dietary doses of caffeine (3.3 mg/kg, equivalent to 2 to 3 cups of coffee), alone and combined with behavioral stress, in men at high risk versus low risk for hypertension. A randomized, double-blind, caffeine-placebo crossover design was used. METHOD: Adrenocorticotropic hormone (ACTH) and cortisol levels in plasma were assessed at rest and in response to 60-minutes of continuous work on a mental stressor (arithmetic) and a psychomotor task (reaction time) on four test sessions held on separate days. RESULTS: Tasks alone caused greater ACTH and cortisol increases in high risk men than in the low risk group. Caffeine alone elevated ACTH and cortisol in both groups, with more immediate responses in the high risk group. Both groups showed significant ACTH and cortisol responses to caffeine plus tasks, with the high risk group showing more persistent elevations. The high risk group also showed the highest levels of ACTH and cortisol after caffeine plus tasks. CONCLUSIONS: These findings demonstrate for the first time the combined effects of caffeine plus stress on ACTH and demonstrate greater corticosteroid effects in hypertension-prone men. As such, they may have implications for the dietary use of caffeine during periods of stress and in those at risk for hypertension.

Adrenocorticotropic Hormone↗