Renal and intestinal calcium-binding proteins in normal and uraemic rats.

The effect of chronic uraemia on the concentrations of the 28 kDa renal and 9 kDa intestinal calcium-binding proteins (calbindin-D28K and calbindin-D9K) was investigated in rats. Calbindin-D9K was measured by a competitive enzyme-linked immunoadsorbent assay and calbindin-D28K by rocket immunoelectrophoresis. Chronic uraemia was induced by 5/6 nephrectomy and the results were compared to sham-operated animals. Rats were fed on a diet containing 0.9% calcium and 1.2% phosphorous. Plasma creatinine and plasma urea were elevated in the nephrectomized rats (p less than 0.001), while plasma-1,25-dihydroxycalciferol vitamin D and fractional calcium absorption were unchanged. Plasma parathyroid hormone was significantly elevated in the uraemic rats. The concentration of calbindin-D28K in renal tissue was increased (p less than 0.001) in rats with chronic uraemia and a direct correlation was found between renal calbindin-D28K and plasma urea (p less than 0.05). Intestinal calbindin-D9K correlated inversely with plasma creatinine (p less than 0.05), but the mean level of calbindin-D9K was unchanged in this model of moderate chronic uraemia. Thus, different regulatory mechanisms control levels of calbindin-D9K and calbindin-D28K.