Dietary calcium supplementation, blood pressure, and intestinal calcium absorption

This study investigated the potential intestinal mechanism in the blood pressure-lowering effect of dietary calcium supplement. Adult Wistar rats received, through a gastrotomy cannula, either 5 or 30 mg elemental calcium.d-1 x 100 g BW-1 for 10 days. At day 11, mean arterial pressure was measured directly in anesthetized animals and calcium absorption determined using an in situ measurement technique of calcium absorption. An intestinal loop (duodenum and proximal jejunum) was perfused both by the intraluminal and the vascular routes. A solution containing 45Ca was perfused intraluminally and the 45Ca appearing in the venous effluent was determined to estimate calcium absorption. Oral calcium supplementation caused intestinal calcium uptake by the isolated loop to increase almost twofold. It also resulted in an 18% increase in mesenteric blood flow. The mean arterial pressure was decreased in calcium supplemented rats compared with control rats (87 +/- 5 vs. 78 +/- 5 mmHg; p < 0.05). These findings could indicate that the passive part of intestinal calcium transport increases in response to dietary calcium supplement. This improvement may participate in the blood pressure-lowering effect of a high calcium diet.