Dietary sodium and potassium-induced transient changes in blood pressure and catecholamine excretion in the Sprague-Dawley rat.

Abstract

When Sprague-Dawley derived rats were changed from a chow type diet to a moderately high sodium diet, rapid transient changes in blood pressure (BP) and catecholamine excretion were observed. After 1 dietary week, BP increased from 122 +/- .1 mm Hg to approximately 145 mm Hg (p less than 0.001), and there was a concomitant 20% reduction in urinary norepinephrine (UNEV) and epinephrine (UEV) excretion (p less than 0.05). Heart rates were reduced (p less than 0.05). These data suggest that sodium-induced increases in BP were initially associated with suppressed sympathetic nervous system activity. During dietary Weeks 2 and 3, some animals had a persistent moderate elevation in BP (BP less than or equal to 150 mm Hg), while others developed more severe increases. UNEV in moderately hypertensive animals returned to control levels during this period; but UEV and heart rates remained suppressed. UNEV in severely hypertensive animals exceeded (13% +/- 3%, p less than 0.05) that of controls. This increase coincided with their most severe hypertension (171 +/- 1 mm Hg, p less than 0.001). UE values and heart rate data indicate that systemic adrenergic tone was likely suppressed at this time and that the increased UNEV was renal in origin. By dietary Week 4, the BP of severely hypertensive animals had begun to fall, and indices of sympathetic nervous system tone were indistinguishable among all groups. Inclusion of a dietary potassium supplement ameliorated the development of hypertension only in those animals that became severely hypertensive, and appeared to prevent the early suppression of indices of sympathetic activity.