O81 EFFECT OF ANTIHYPERTENSIVE MEDICATIONS ON URINARY SODIUM TO POTASSIUM (Na/K) RATIO

Background: The urinary sodium to potassium ratio (Na/K) greater than 2 indicating either excess sodium or insufficient potassium intake. However, the effect of antihypertensive medications on the urinary Na/K ratio has not been evaluated. We hypothesized that antihypertensive medication would acutely affect the urinary Na/K ratio. Methods: Male and female C57BL/6J mice, 14 weeks old, and a separate cohort of 24-month-old mice were subjected to a regular chow diet (NaCl 0.4%) and a high salt diet (4%). Urinary Na/K ratios in spot urine samples were measured three times a week. After baseline measurements, all animals were treated with one antihypertensive medication for 2 weeks, followed by a one-week washout period. The effects of enalapril (25 mg/kg/day), hydrochlorothiazide (25 mg/kg/day), and amlodipine (10 mg/kg/day)—were compared under a high salt diet mimicking human salt consumption. Urinary Na/K ratios collected on day 1 (acute) and day 8 (subacute) after initiating medication were compared to the vehicle period using a two-way ANOVA. Medication was administered with food using gel food pellets. Results: Under regular chow, the urinary Na/K ratio was 0.65±0.58 (n=15) with no interaction between sex or age (all p>0.05). Under a high salt diet, the urinary Na/K ratio increased to 4.5±2.2 (p<0.01 vs. regular chow) with no differences between sex and age. After the washout period, enalapril, both acutely and subacutely, did not affect the Na/K ratio. Similarly, hydrochlorothiazide did not affect the Na/K ratio in either period. However, amlodipine reduced the Na/K ratio in both acute and subacute periods (p<0.001). No interaction was observed with sex or age. The effect of amlodipine was related to higher potassium excretion (43.9±23 vs. 81.6±33 meq/L; p<0.001) with no changes in sodium excretion (152.2±75 vs. 173.3±43.5 meq/L; p=0.8). Conclusion: The Na/K ratio reflects salt and potassium consumption. The Na/K ratio is not affected by enalapril or hydrochlorothiazide. Amlodipine decreases the Na/K ratio acutely and subacutely due to increased potassium excretion.