Prolonged isometric exercise. Part 2: Effect on circulation and on renal excretion of sodium and potassium in young males genetically predisposed to hypertension

Cardiovascular and renal responses to mental challenge in highly and moderately active males with a family history of hypertension

The objective of this study was to compare FBF and renal responses to mental challenge in highly and moderately active males with a family history of hypertension. Normotensive, healthy males with a family history of hypertension (n = 18) were recruited into moderately active and highly active groups. Cardiovascular, FBF, and renal responses to a 10-min Stroop mental challenge were measured. Urine was analysed for levels of sodium and potassium pre and post stressor as an indicant of renal blood flow. The results were that the moderately active males demonstrated a significantly higher level of FBF reactivity to mental challenge compared with that of the highly active. Heart rate change and FBF change during the stressor were positively correlated (r = 0.75, P < 0.01). Both groups, however, demonstrated a similar pattern of sodium excretion to mental challenge. These findings suggest that physical activity level is associated with FBF reactivity but not renal reactivity to mental challenge in offspring hypertensives. That sodium excretion was no different post-stressor in the moderately active group suggests that the exaggerated forearm vasodilatation response was not due to renal vasoconstriction.

Stress-induced changes in the rate of sodium excretion in healthy black and white men

The effects of exposure to competitive mental stressors on rates of excretion of sodium (Na), potassium (K) and fluid, together with cardiovascular responses, were evaluated in 14 black and 14 white normotensive men after 3 days of controlled diet (200 mEq Na, 100 mEq K daily). In the first hour of a 5-hr protocol, subjects ingested a standard dinner and drank 1 liter of water. In hours 2-5, they voided to provide urine collections every 30 min, and drank 200 ml additional water after each collection. Hours 1-2 were for stabilization of excretion, hour 3 was baseline, hour 4 was stress and hour 5 was post-stress rest. During stress, 20 men showed faster natriuresis and 8 showed slower natriuresis than at baseline. These subgroups did not differ in any excretion measure at baseline. During stress, the slow stress natriuresis group showed slower excretion of potassium and fluid as well as sodium; slow natriuresis and kaliuresis persisted 30 min after stress. Creatinine clearance rate was also decreased, but only during the first 30 min of stress. Slow stress natriuresis subjects were found to have higher blood pressures during baseline and stress, greater heart rate and cardiac output increases during stress, and a larger percentage had hypertensive parents (63 vs 37%) compared to fast stress natriuresis subjects. Slow stress natriuresis was observed in 50 vs 17% of men with resting diastolic levels above vs below 80 mmHg, and in 43% of blacks vs 18% of whites tested. Overall, black subjects tended to excrete sodium more slowly than whites at baseline, and showed significantly lesser increases in sodium excretion rate when pressures rose during stress.

Relation between arterial pressure, dietary sodium intake, and renin system in essential hypertension

Forty-one patients with mild essential hypertension, 36 patients with severe hypertension, and 28 normotensive subjects were studied on a high sodium intake of 350 mmol/day for five days and low sodium intake of 10 mmol/day for five days. The fall in mean arterial pressure on changing from the high-sodium to the low-sodium diet was 0.7 +/- 1.7 mm Hg in normotensive subjects, 8 +/- 1.4 mm Hg in patients with mild hypertension, and 14.5 +/- 1.4 mm Hg in patients with severe hypertension. The fall in blood pressure was not correlated with age. Highly significant correlations were obtained for all subjects between the ratio of the fall in mean arterial pressure to the fall in urinary sodium excretion on changing from a high- to a low-sodium diet and (a) the level of supine blood pressure on normal diet, (b) the rise in plasma renin activity, and (c) the rise in plasma aldosterone. In patients with essential hypertension the blood pressure is sensitive to alterations in sodium intake. This may be partly due to some change either produced by or associated directly with the hypertension. A decreased responsiveness of the renin-angiotensin-aldosterone system shown in the patients with essential hypertension could partly account for the results.