Characteristics of individuals who excrete versus retain sodium under stress

To examine the role of stress on renal sodium excretion, we studied 27 normotensive and 21 hypertensive subjects. All subjects were placed on a standardized sodium diet. After water loading (2290 ml in 3 1/2 hr) they completed a 30 min baseline and a 30 min stress period (competitive videogame). Sixty-nine percent of the subjects increased ("excreters") and 31% decreased ("retainers") their sodium excretion under stress. In addition to increased potassium excretion (p < 0.006), excreters also manifested less of a stress associated increase in systolic (p = 0.055) and diastolic (p = 0.040) blood pressure and showed greater expression of anger (p < 0.02) than retainers. The same subjects were also studied to determin the effects of angiotensin converting enzyme inhibition (captopril 25 mg b.i.d.) on sodium excretion. On captopril, excreters now showed a retention of sodium (p < 0.001) and potassium (p < 0.01) under stress and no longer differed significantly in blood pressure reactivity. The results suggest that there are two different stress-related patterns of renal sodium excretion, that these patterns are related to blood pressure responses to stress, and may be related to anger expression. In addition, sodium excretion patterns under stress may be altered with certain type of antihypertensive medications.