1. We evaluated the effects of the dietary restriction of sodium chloride on blood pressure and systemic calcium metabolism in 19 in-patients with essential hypertension (11 men and 8 women, mean age 49.9 ± 12.1 years).

2. All patients received a high-sodium diet (250 mmol/day) for 1 week, followed by a low-sodium diet (10 mmol/day) for another week. Intake of potassium (100 mmol/day) and of calcium (15 mmol/day) were kept constant throughout the study.

3. Sodium restriction significantly reduced the mean blood pressure (from 114.0 ± 1.9 to 105.0 ± 13.7 mmHg, P < 0.01). Urinary calcium excretion was significantly reduced (from 5.1 ± 2.4 to 2.2 ± 1.0 mmol/day, P < 0.01).

4. The change in mean blood pressure after sodium restriction was not correlated with a change in any parameter of calcium metabolism [whole blood ionized calcium, plasma intact parathyroid hormone, or 1,25-(OH)2 vitamin D3].

5. Plasma renin activity during a regular sodium diet, an index of renin status, was significantly and inversely correlated with the change in blood pressure during sodium restriction, but not with any change in the parameters of calcium metabolism.

6. We conclude that sodium restriction reduces blood pressure and decreases urinary calcium excretion. However, we observed no significant role of extracellular calcium concentration or of calciotropic hormone concentration in the mechanism of sodium sensitivity.

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