Effects of dietary calcium on renal calcium, magnesium and phosphate excretion by the rabbit.

The renal handling of calcium, phosphate and magnesium was evaluated in rabbits fed diets varying in calcium content. Rabbits fed a low calcium diet (0.29%) exhibited a significant decrease in 24-hour excretion of calcium and in plasma calcium, and a significant increase in 24-hour excretion of phosphate, compared with rabbits fed a normal calcium diet (0.61%). Rabbits fed a high-calcium diet (1.89%) excreted significantly more calcium and less phosphate than the group fed normal dietary calcium. When measured under acute clearance conditions, the fractional excretion of calcium averaged 1-2% in rabbits fed either the low- or normal-calcium diets and increased to 6% in rabbits fed the high-calcium diet. In both acute and chronic studies, fractional phosphate excretion declined as the content of dietary calcium was raised. Magnesium excretion was not altered by the dietary calcium levels. Although calcium excretion by rabbits is set proportionately higher than that of other species, renal calcium handling in the rabbit is appropriate. Phosphate handling by the rabbit kidney similarly responds appropriately to dietary calcium manipulation.