Studies on vitamin D binding protein in the nephrotic syndrome

We studied the properties of vitamin D binding protein in plasma and urine from nine patients with nephrotic syndrome. Samples were incubated with 25-[3H]hydroxyvitamin D3, after which we determined binding capacity and apparent dissociation constants. Binding capacity was markedly less in plasma from patients with nephrotic syndrome than that from normal subjects, but binding affinity was unchanged. Specific binding of 25-hydroxy[3H]vitamin D3 could be demonstrated in urine from all the nephrotic patients, and sucrose density-gradient analysis of these urines revealed a single binding peak with sedimentation characteristics similar to those of vitamin D binding protein in plasma.