HIGH-CALCIUM DIET, DIFFERENT ANTIHYPERTENSIVE AGENTS, AND CYTOSOLIC-FREE CA2+ IN SPONTANEOUSLY HYPERTENSIVE RATS

Several studies have shown that increased dietary calcium decreases blood pressure (BP) in spontaneously hypertensive rats (SHR), but the underlying mechanisms are not fully understood. We compared the effects of a high calcium diet and different antihypertensive agents on BP and intracellular free Ca2+ concentration ([Ca2+]i) in lymphocytes of adult SHR. The calcium content of the normal chow was 1.1% and that of the high calcium chow was 2.5%. Antihypertensive drug treatments were performed by giving the animals trichlormethiazide (2 mg/kg/day), atenolol (25 mg/kg/day), and quinapril (10 mg/kg/day) in drinking water. Untreated SHR and normotensive Wistar-Kyoto (WKY) rats served as controls. After 14 weeks of study systolic BP (SBP) and [Ca2+]i in blood lymphocytes, measured with a fluorescent indicator quin-2, were higher in untreated SHR than in WKY rats. Trichlormethiazide, atenolol, quinapril, and the high calcium diet all decreased BP in SHR, but only quinapril and calcium-rich diet concurrently reduced [Ca2+]i. We conclude that the reduction in [Ca2+]i during high calcium intake does not result from decreased BP itself. If the changes in lymphocyte [Ca2+]i reflect Ca2+ metabolism in other tissues as well, especially in vascular smooth muscle, the normalization of [Ca2+]i may be involved in the BP-lowering mechanisms of oral calcium loading and angiotensin-converting enzyme (ACE) inhibition in genetic hypertension.