Effect of long-term dietary calcium supplementation on blood pressure in rats

The anti -hypertensive effect of high dietary calcium supplementation has been controversial. The purpose of this study was to investigate the effect of dietary calcium supplementation on blood pressure in spontaneously hypertensive rats (SHRs) and acquired hypertension rats (AHRs). Prior to dietary treatments, the Wistar rats were nephrectomized (left kidney) and treated with deoxycorticosterone acetate (DOCA)/salt diet for 4 weeks to induce hypertension and become AHRs. Then, the SHRs and AHRs were treated with either high calcium (1.28% Ca as calcium carbonate) or low calcium (0.2% Ca) diet for 30 weeks. Blood pressure, calcium balance, and calcium and phosphorus contents in bones were examined during the experimental period. The AHRs consuming high calcium diets had lower blood pressure at week 15 than those consuming low calcium diet. Additionally, the high calcium diet group in the AHRs had increased serum calcium levels at week 10 compared with the low calcium diet group, suggesting that increased extracellular calcium concentration can be related to the decreased blood pressure. However, except for increased fecal calcium excretion in high calcium diet group, no significant differences for blood pressure, and calcium levels in serum and urine were observed between high calcium and low calcium diet groups in the SHRs. Serum sodium levels tended to decrease in the AHRs at week 30, suggesting that lower blood pressure in high calcium supplemented AHRs may be due to the decreased serum sodium levels. Bone calcium contents were not significantly different between high calcium and low calcium diet groups for either SHRs or AHRs. Bone phosphorus contents were lower at week 30 in high calcium supplemented SHRs.