RELATION OF PLASMA-RENIN TO END ORGAN DAMAGE AND TO PROTECTION OF K plus FEEDING IN STROKE-PRONE HYPERTENSIVE RATS

We studied the effects of regular diet (0.35% NaCl/1.1% potassium), high sodium diet (4% NaCl/0.75% potassium), or high sodium and high porassium diet (4% NaCl/2.11% potassium) on blood pressure, plasma renin activity, renal and cerebrovascular lesions, and incidence of stroke and mortality in male stroke-prone spontaneously hypertensive rats (SHRSP). In the first 4 weeks, the rise in blood pressure was higher in high NaCl than in high NaCl/high potassium or regular diet groups. However by 8 to 12 weeks, the blood pressure in all three groups was similar. After 4 weeks of diet, plasma renin activity was similar in the three groups (3.4±0.8, 4.1±0.9, and 5.2±1.6 ng/ml/hr, in high NaCl, high NaCl/high potassium, and regular diet groups, respectively) and were not related to sodium excretion. After 8 weeks, plasma renin activity was significantly increased only in the high NaCl group (13.7±3.7 ng/ml/hr), and by 12 weeks plasma renin activity was significantly higher in the high NaCl group (25.3±3.6 ng/ml/hr) than in the high NaCl/high potassium (11.1±2.9 ng/ml/hr) or in the regular diet (7.8±4.6 ng/ml/hr) groups. Moderate to severe renal vascular lesions were first detected in the high NaCl group by 8 weeks of diet. At 12 weeks, renal vascular damage index (RVDI), estimated histologically, was significantly higher in the high NaCl group (RVDI=79±14) than in the high NaCl/high potassium (RVDI=40±11) and regular diet (RVDI=7.8±4.6) groups. At this time, incidence of stroke was 81% in high NaCl, 24.5% in high NaCl/high potassium, and 7.7% in regular diet groups. The data demonstrate that: 1) the increase in mortality, stroke, and renal and cerebrovascular lesions in SHRSP fed a high sodium diet is associated with a paradoxical rise in plasma renin activity; 2) the protective effect of high potassium in SHRSP fed a high potassium diet is related to a lower blood pressure at 2-4 weeks and a lower plasma renin activity, but not a lower blood pressure at 8-12 weeks; 3) this rise in plasma renin activity demonstrates that a high potassium diet suppresses or delays a primary or secondary paradoxical rise in plasma renin activity and thus, angiotensin II in the rats fed a high sodium diet. This action together with possible direct effects of potassium in the vasculature contributes to the protective effect on end organ damage and stroke in SHRSP.