Dietary calcium restriction induces salt‐sensitive hypertension in normal rats

Abstract

Numerous studies report an inverse relationship between blood pressure and calcium (Ca) intake, such that increased dietary Ca retards the development of salt‐sensitive hypertension in humans and animal models. We hypothesized the converse; that dietary Ca restriction would exaggerate the increase in blood pressure in response to a high sodium (Na) diet. 18 young Sprague Dawley rats were placed on isocaloric diets over 7 weeks, containing either normal Na (0.22%)/low Ca (0.15%), high Na (3.2%)/ normal Ca (1.36%), or high Na/low Ca. Systolic blood pressure (SBP) was measured by tail‐cuff plethsmography. All rats grew at the same rate (32 ±1 g/week). Baseline SBP was 129 ±2 mmHg. In normal Na/low Ca rats SBP increased 9 ±3 mmHg over the first 3 weeks, then returned to baseline. In high Na/normal Ca rats, SBP increased by 20 ± 4 mmHg over the first 3 weeks (p<0.05), returning to baseline by week 6. The combination of high Na/low Ca evoked a 26 ±3 mmHg increase in SPB over the first 3 weeks (p<0.05) and remained elevated by 15 ±2 mmHg after 7 weeks on this diet (p<0.05). Plasma renin activity was supressed by high Na diet similarly without or with low Ca (4.3 ±1.0 vs. 1.4 ±0.3* vs. 1.2 ±0.3* ngAngI/ml/hr, respectively, *p<0.005). Our findings suggest that dietary Ca restriction exaggerates and sustains the hypertensive response to excess dietary Na, inducing a salt‐sensitivity in otherwise normal rats.