Effect of dietary calcium intake and protein source on calcium utilization and bone biomechanics in the spontaneously hypertensive rat

Abstract

The effects of dietary calcium level and protein source on in situ paracellular Ca absorption, and subsequent Ca utilization for bone mineralization and biomechanical strength were examined in spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats fed 20% casein and soy protein isolate diets containing different levels of calcium (2.0, 0.5 and 0.05% wt/wt). Rats were meal fed for 10 weeks after which calcium absorption was measured by the disappearance of 45Ca from the ligated ileal loop. Femoral deposition of 45Ca, and femur and tibia mineral composition were also examined. Calcium utilization was estimated from femur and tibia biomechanical measurements. The greater ( P < 0.05) bone mineralization observed in SHR compared to WKY in animals fed high and adequate Ca-containing diets was not attributable to the relative efficiencies of paracellular calcium absorption and had little effect on femur biomechanical force parameters. In both Ca replete SHR and WKY, the greater bone mineralization observed in casein-fed compared with soy-fed counterparts was reversed when animals were fed calcium deficient diets. Calcium absorption in situ was affected equally in both SHR and WKY ( P < 0.05) by differences in dietary calcium intake as well as protein source. Similarly, in both animal strains, bone biomechanical strength parameters were correlated with bone mineralization, which in turn was influenced more by dietary calcium than protein source.