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

Several studies have shown that increased dietary calcium decreases bl ood pressure (BP) in spontaneously hypertensive rats (SHR), but the un derlying 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 adu lt SHR. The calcium content of the normal chow was 1.1% and that of th e high calcium chow was 2.5%. Antihypertensive drug treatments were pe rformed by giving the animals trichlormethiazide (2 mg/kg/day), atenol ol (25 mg/kg/day), and quinapril (10 mg/kg/day) in drinking water. Unt reated SHR and normotensive Wistar-Kyoto (WKY) rats served as controls . After 14 weeks of study systolic BP (SBP) and [Ca2+]i in blood lymph ocytes, measured with a fluorescent indicator quin-2, were higher in u ntreated SHR than in WKY rats. Trichlormethiazide, atenolol, quinapril , and the high calcium diet all decreased BP in SHR, but only quinapri l and calcium-rich diet concurrently reduced [Ca2+]i. We conclude that the reduction in [Ca2+]i during high calcium intake does not result f rom decreased BP itself. If the changes in lymphocyte [Ca2+]i reflect Ca2+ metabolism in other tissues as well, especially in vascular smoot h muscle, the normalization of [Ca2+]i may be involved in the BP-lower ing mechanisms of oral calcium loading and angiotensin-converting enzy me (ACE) inhibition in genetic hypertension.