Increased calcium intake reduces plasma cholesterol and improves vasorelaxation in experimental renal failure

Chronic renal failure (CRF) is associated with abnormal lipid metabolism and high prevalence of vascular complications. Calcium salts are commonly used in CRF as phosphate binders. Increased calcium intake may also lower plasma cholesterol and beneficially influence vascular tone. Therefore, we investigated the influence of increasing dietary calcium from 0.3% to 3.0% for 8 wk after 5/6 nephrectomy (NTX) on plasma cholesterol and mesenteric resistance vessel tone in male Sprague-Dawley rats. The groups were Sham, Sham-Calcium, NTX, and NTX-Calcium (n = 10-11). Blood pressure was modestly elevated after NTX, whereas the plasma creatinine, urea nitrogen, phosphate, and parathyroid hormone levels were clearly increased. The high-calcium diet suppressed plasma phosphate and parathyroid hormone but was without effect on blood pressure. The NTX resulted in 1.6-fold elevation in plasma total cholesterol and 40% reduction in high density-to-low density lipoprotein ratio (HDL/LDL). However, the lipid profile in NTX rats on the high-calcium diet did not differ from sham-operated controls. The endothelium-mediated relaxations induced by acetylcholine were impaired in NTX rats, whereas the response was normalized by a high-calcium diet. No differences in vasorelaxations by the endothelium-independent vasodilator nitroprusside were detected. In conclusion, improved vasorelaxation after a high-calcium diet could be due to reduced plasma total cholesterol and ameliorated HDL/LDL ratio, although decreased plasma phosphate and parathyroid hormone may also play a significant role in the vascular effects of increased calcium intake.