Effect of variations in dietary calcium on renal and intestinal calcium-binding proteins

This study was designed to determine if protein-induced calciuria was related to alterations in the intestinal and renal calcium-binding proteins (CaBP). Weanling Sprague-Dawley rats were fed diets containing low, normal, or high Ca and protein diets for 2 wk. Twenty-four-h urine and fecal samples were collected before the termination of the study. Plasma, kidney, duodenum, ileum, and femur samples were obtained for selected mineral and CaBP analyses. Growth was significantly depressed on the low protein diets and this was independent of Ca levels. Hypercalcemia, hypercalciuria, and increased renal CaBP were associated with the high Ca intakes but not with the high protein diets. It is suggested that in conditions where Ca intakes are high, the renal CaBP has a role in Ca excretion and responds to changes in Ca concentrations occurring in the distal tubule. No loss of femur Ca was seen in rats on the high protein diets.