Relationships between Plasma Renin Activity and Plasma Aldosterone in the Rat after Dietary Electrolyte Changes

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Abstract
The relationships between plasma rennin activity (PRA) and plasma aldosterone were evaluated in rats maintained on altered dietary sodium or potassium intake for 6 weeks. A bivariate method of analysis was utilized to determine the correlations between these two dependent variables in the presence and absence of anesthesia for blood collection. Sodium restriction had a direct stimulatory effect on both renin and aldosterone, and a high sodium diet had the opposite effect. A significant positive correlation was observed between PRA and plasma aldosterone with variations in dietary sodium intake either in the presence (r = 0.79, P < 0.001) or absence (r = 0.67, P < 0.001) of anesthesia for blood collection. With variations in dietary sodium intake, linear changes in PRA were accompanied by logarithmic changes in plasma aldosterone. Varying potassium intake caused a negative correlation between PRA and aldosterone. High potassium intake was accompanied by significant suppression of PRA and marked stimulation of aldosterone production, to a degree that exceeded low sodium intake. In contrast, low potassium intake was associated with a 7-fold increase in PRA, with no increment in aldosterone production. The influence of dietary maneuvers on renin and aldosterone was not obscured by anesthesia. However, anesthesia had a more pronounced acute stimulatory effect on renin than on aldosterone secretion. These findings demonstrate that variations in either sodium or potassium intake in the rat influence adrenal sensitivity to the renin-angiotensin system.