Effects of calcium infusion on blood pressure in hypertensive and normotensive humans.

Disorders of calcium and parathyroid hormone homeostasis have been reported in subjects with essential hypertension. In many of these studies, dietary intakes of sodium and calcium were not carefully controlled. The present study was designed to compare calcium and parathyroid hormone homeostasis in normal and hypertensive subjects on controlled dietary sodium and calcium intakes and to examine the impact of dietary sodium loading on hemodynamic and metabolic responses to infused calcium. Seven subjects with essential hypertension and seven age-matched and sex-matched controls were studied while consuming a standard diet containing 600 mg of elemental calcium. Each subject was studied while consuming 10, 160, and 510 mEq of sodium per day, before, during, and after a 3-hour calcium infusion (3.75 mg/kg/hr). Before calcium infusion, hypertensive subjects had increased urinary cyclic adenosine 3',5'-monophosphate excretion independent of sodium intake (p less than 0.05). Urinary potassium excretion was greater in normotensive than in hypertensive subjects (p = 0.002). At baseline, dietary sodium intake had no effect on systolic, diastolic, or mean arterial pressure. During calcium infusion, systolic pressure increased in both groups, whereas diastolic pressure increased only when dietary sodium content was high and mean arterial pressure increased only in hypertensive subjects (p = 0.007). Together, these data provide evidence for interactions between dietary sodium intake and the cardiovascular response to calcium. They confirm that hypertensive subjects exhibit enhanced parathyroid gland function even when dietary factors are controlled, and they suggest that these subjects are more sensitive to the cardiovascular effects of short-term calcium infusion.