Norepinephrine content of discrete brain nuclei in acutely and chronically stressed borderline hypertensive rats.

Forty-three male borderline hypertensive rats were subjected to either 3 days, or 4, 10, or 16 weeks of daily stress. An additional 43 animals served as unstressed, age-matched controls. At the end of study, animals were sacrificed, brains were removed, and cardiovascularly-important nuclei in the brainstem and hypothalamus were removed by micropunch. Assays revealed that norepinephrine (NE) levels were initially elevated in the brainstem in animals stressed for 3 days. As stress continued, NE levels were significantly lower in the brainstem, and eventually in the hypothalamus, of stressed animals. The relationship of these observations to environmentally-induced hypertension is discussed.

Bilateral renal denervation can prevent the development of stress-induced hypertension in the borderline hypertensive rat.

The borderline hypertensive rat (BHR) shows large blood pressure responses to either stress or a high salt diet. Since the renal nerves have been shown to play a role in several animal models of hypertension, the current study sought to determine the effect of bilateral renal denervation on the development of stress-induced hypertension in the BHR. BHR were deprived of renal nerves under ether anesthesia after either 5 or 11 weeks of daily 2-hour stress sessions. Additional BHR received sham surgery. Unstressed BHR, age-matched to stressed groups, received denervation or sham surgery. Following a 3 week recovery period, the protocol (stress or no stress) was continued for 10 additional weeks. Tail cuff systolic blood pressures were obtained weekly. BHR stressed for 5 weeks prior to denervation failed to develop hypertension in response to continued stress. Although BHR stressed for 11 weeks prior to denervation showed a temporary reduction in pressure following denervation, blood pressure returned to the hypertensive levels of sham-operated controls after several weeks. Thus, there may be a critical period during which the renal nerves are necessary for the expression of stress-induced hypertension in the BHR. These observations are discussed in relation to the effects of renal denervation on hypertension in various animal models.

The borderline hypertensive rat: a model for studying the mechanisms of environmentally induced hypertension.

The borderline hypertensive rat (BHR) is a first-generation cross between the spontaneously hypertensive rat and the normotensive Wistar-Kyoto rat. The BHR develops frank hypertension when chronically stressed or when fed a high-sodium diet. Stress-induced hypertension can be blocked by exercise. The role of the central nervous system and kidney in hypertension development in this model is discussed.

Type A behavior pattern, parental history of hypertension, and cardiovascular reactivity in college males.

Two risk factors for cardiovascular disorders, parental history of hypertension and the Type A behavior pattern, were investigated concurrently with respect to cardiovascular reactivity to challenging situations. Sixty-four college males were given both the Structured Interview (SI) and Jenkins Activity Survey (JAS) for the Type A behavior pattern and a family health questionnaire to determine parental history of hypertension. The students were monitored for blood pressure (BP), heart rate (HR), and pulse transit time (PTT) response to four tasks: cold pressor, isometric handgrip exercise, a reading comprehension task, and backwards digit span. Type As based on SI classification had significantly higher HR levels across all tasks than did Type Bs, as well as higher diastolic BP levels in the cold pressor task. No main effects for Type A-B using JAS classification were found. Positive parental history students had higher HR and shorter PTT levels across all the tasks. Type A and parental history did interact in a limited way on some tasks, but the interactions were also dependent on the Type A classification used.

Exercise training attenuates stress-induced hypertension in the rat.

The ability of exercise training to block the generation of hypertension produced by chronic stress in the borderline hypertensive rat was tested. Twenty-three male borderline hypertensive rats, F1 offspring of spontaneously hypertensive and Wistar-Kyoto rats, were divided into three groups. Two groups (8 rats per group) were subjected to 2 hours of daily, predictable, uncontrollable tail shock for 12 weeks. One of these groups was also given 2 hours of daily swim stress (exercise trained). A third group served as a maturation control and received neither intervention (n = 7). After 12 weeks of stress, direct recording of blood pressure verified the pattern observed with tail cuff: shock only group, 180/118 +/- 3/3 mm Hg; exercise-trained and shocked group, 166/108 +/- 4/2 mm Hg; and control group, 160/98 +/- 6/4 mm Hg (mean +/- SEM). Systolic and diastolic blood pressures in the shock only group were significantly higher than in both the other groups (p less than 0.05). The control group differed from the exercise-trained and shocked group only in diastolic BP (p less than 0.05). During a short-term stress session plasma norepinephrine levels in the exercise-trained and shocked group were significantly lower than those in the shock only group (555 +/- 56 vs 776 +/- 84 pg/ml; p less than 0.05). These results indicate that an alteration of autonomic function resulted from the exercise training, but its contribution to the resistance of the exercise-trained and shocked rats to stress-induced hypertension is unclear.

Blood pressure and heart rate responses to environmental stress in the spontaneously hypertensive rat.

Blood pressure and heart rate responses of the spontaneously hypertensive rat (SHR) and the Wistar-Kyoto rat (WKY) to mild restraint and tone-shock pairings were compared during a pre-stress, aversive conditioning and post-stress period, after five previous days of exposure to the paradigm. Although SHR and WKY showed similar responses to the onset of the pre-stress period, SHR showed significantly larger blood pressure responses following the onset of the conditioning than WKY. Furthermore, WKY showed a significant blood pressure and heart rate reduction during the conditioning session which was absent in the SHR. During the post-stress period, the blood pressure of SHR remained significantly elevated compared to their home cage rest values, but the blood pressure of WKY returned to basal levels. It is concluded that while the SHR is more reactive than the WKY to stimulus onset, the major source of between-strain differences after 20 min relates to differences in adaptation to continued environmental stimulation. This can lead to exaggerated estimates of physiological reactivity of the SHR, and is supportive of Folkow's view that SHR are both hyperreactive and show more prolonged defense reactions.

Cardiovascular and sympathoadrenal responses to stress in swim-trained rats.

Chronic exposure to swim stress (i.e., training) is associated with functional adaptations of the cardiovascular system. On the other hand, repeated exposure to tail shock, an emotional stress, often results in deleterious changes in resting blood pressure and myocardial pathology. We hypothesized that the pathological adaptation following chronic exposure to tail shock was associated with a larger acute physiological response compared with swim stress. Therefore, acute responses to swim and shock stress were compared. A second concern of this study examined the extent to which adaptation to swim training influences responses to predictable tail shock stress. The cardiovascular and sympathoadrenal responses to swim stress, using 1% body wt attached to the tail, were compared with predictable tail shock (0.2-0.4 mA intensity, 1-s duration, 1/min) in two groups of Long-Evans male rats. In the first, 11 rats were studied following 5-7 wk of swim training, consisting of daily 1-h sessions of swimming with 2% body wt attached to their tails. They were compared with an age-matched nontrained (NT) group (n = 8). During swimming, the trained animals showed significantly lower heart rate (387 +/- 10 vs. 449 +/- 18 beats/min) and significantly lower lactate (0.9 +/- 0.09 vs. 2.0 +/- 0.24 mmol/l), epinephrine (332 +/- 57 vs. 739 pg/ml), and corticosterone (32 +/- 10 vs. 62 +/- 9 micrograms/dl) responses. Systolic and diastolic blood pressures were elevated in swim stress by the same degree in trained (167/110 mmHg) and NT (177/116 mmHg) rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Type A behavior and physiological responsivity in young women.

The purpose of this study was to assess the coronary-prone behavior pattern and physiological responses to stress in young women. Thirty-seven women, aged 18-25 yr, were tested; half were studying in nontraditional fields for women, half in traditional. Based on the Jenkins Activity Survey, women in the male-dominated fields of study were more Type A. Subjects were monitored while resting and while solving mental arithmetic problems and visual puzzles; the dependent variables were heart rate, and blood pressure. Comparisons were made based on both the Jenkins Activity Survey and the structured interview, and using both median splits and extreme groups. There were no physiological differences between Types A and B women. Possible methodological issues accounting for the lack of results are considered.