BLOOD PRESSURE EFFECTS OF BEHAVIORAL STRESS / SODIUM LOADING

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This study examines the physiological and psychological factors associated with blood pressure elevations in normotensive adults. The long-term goal of this research is the development and refinement of preventative interventions for hypertension, either behavioral or dietary, that can be directed at those individuals who are most vulnerable to the synergistic blood pressure effects of behavioral stress and a high sodium intake. Medical students at Johns Hopkins University School of Medicine participated in two different parts of the study, once during the two-week examination period and once during a stressful laboratory protocol. Forty-two medical students wore ambulatory blood pressure monitors during a lecture and during the examination while maintaining the high sodium (N=28) and regular sodium intake (N=14). The stress of taking an examination was associated with a lowering of plasma potassium, an increase in plasma cortisol, and a tendency to increase plasma sodium. As expected, blood pressure and heart rate were elevated during the examination relative to the lecture period, but the magnitude of these elevations were not influenced by sodium intake. Timed urine samples were collected and the examination was associated with a reduction in urinary excretion rate, although both urinary cortisol and urinary norepinephrine tended to increase during the stressful examination. Urinary cortisol excretion during the examination was greater among the high sodium group, whereas urinary norepinephrine excretion tended to be lower in the high sodium group. Urinary sodium excretion data were used to identify subsets of individuals, including sodium retainers (48% decreased urinary sodium excretion rate (Una) during the exam relative to the lecture) and sodium excreters (52% increased Una). Sodium retainers showed higher sodium excretion rates during the control (lecture) conditions and lower sodium excretion rates during exposure to the stressor. These individuals also showed lower overnight sodium excretion before the stressful examination. Sodium retainers showed a tendency for greater blood pressure reactivity to the stressful examination, a tendency for higher levels of urinary norepinephrine excretion during the examination, and a tendency for higher resting levels of aldosterone collected 30 minutes before the exam. In a second study, medical students (N=7) completed a 4.5 hr laboratory protocol designed to examine acute cardiovascular, neurohormonal, and renal responses to a stressful interview. Stress- induced sodium retention was observed in 29% of the sample. Preliminary results indicate that stress-induced sodium retention was associated with higher levels of plasma adrenocroticotrophin hormone and aidosterone levels, although both groups showed comparable blood pressure elevations in response to the stressful interview. Stressinduced sodium retention was observed to continue into the one- hour recovery period. These findings suggest the importance of adrenocortical activation, particularly aldosterone stimulation, in response to behavioral challenges as a possible mediator of stress- related sodium retention.