The American journal of the medical sciences
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To investigate the quantitative importance of sodium balance to arterial pressure changes produced by changes in sodium intake, we studied normotensive white and black subjects and hypertensive black patients with two protocols. Protocol 1 used a 3-day control period with a 150 mEq sodium intake/day followed by 4 days of salt depletion (SD) with a diet providing 9 mEq/day of sodium and furosemide, 1 mg/kg, given the first day and then 3 days of salt loading (SL), during which 25 mL/kg of isotonic sodium chloride solution was given intravenously each day (3.88 mEq sodium/kg/day). In protocol 2, the sequence of sodium intake changes was reversed. ⋯ In protocol 1, the hypertensives had statistically significant changes in arterial pressure with changes in salt intake, and they also lost more sodium than normotensives during SD. In protocol 2, blacks, both normotensives and hypertensives, had statistically significant pressure changes with both SL and SD, and black hypertensives retained less sodium during SL than either normotensive group. Spearman correlations showed no relationship between sodium balance and mean arterial pressure, suggesting that salt-sensitive hypertension results not from the magnitude of sodium retention, but from the pressor mechanisms evoked.
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Comparative Study
Vasopressin: sexual dimorphism in secretion, cardiovascular actions and hypertension.
We have investigated the issue of sexual dimorphism in the secretion of vasopressin, its pressor action, and the development of deoxycorticosterone (DOC)-salt hypertension. In normal human subjects on controlled salt intake, the basal secretion of vasopressin, indicated by plasma vasopressin levels and urinary excretion of vasopressin, was higher in men than in women and in blacks than in whites. Basal vasopressin secretion also was higher in male than in female rats. ⋯ Finally, DOC-salt hypertension, which is dependent on vasopressin, developed more rapidly in male than in female rats. Although there was no sex-related difference in the extent to which plasma vasopressin levels were elevated, pressor responsiveness to vasopressin was greater and baroreflex sensitivity was attenuated to a lesser extent in hypertensive males than in hypertensive females. Thus, it seems likely that gonadal hormones play a significant role in cardiovascular regulation.
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The responses to sodium depletion and repletion were studied in subgroups of 92 normotensive and 65 borderline hypertensive individuals. The borderline hypertensives were characterized by significantly higher blood pressure, weight, cardiac output, hematocrit and decreased density of conjunctival capillaries and venules. ⋯ Sodium-sensitive individuals were characterized by significantly increased forearm vascular resistance and decreased plasma renin activity and aldosterone concentration. The resemblance of these changes to those reported in the Dahl salt-sensitive rat suggests a genetic basis for the response to sodium.
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Hypertension can precipitate renal failure in blacks. The key hypertensive lesion in the renal vasculature is severe intimal thickening in interlobular arteries without fibrinoid necrosis. ⋯ In view of this, it is likely that the low K diet characteristically consumed by blacks exaggerates their hypertensive intimal thickening. A high K diet could possibly preserve these arteries and avert much renal failure.