Ligand blot of circulating IGFBP-1 in normal individuals and patients with PV. A representative ligand blot shows plasma levels of IGFBP-1 in PV patients and normal individuals (N). Plasma samples from 2 PV patients and 2 age- and sex- matched normals were used to immunoprecipitate IGFBP-1 and these were separated by SDS-polyacrylamide gel electrophoresis under nondenaturing conditions, transferred to nitrocellulose membrane, and ligand blotted with ¹²⁵I–IGF-I. The membrane was then washed and used to expose x-ray film. Recombinant human IGFBP-1 (UBI) was run as a positive control and C indicates a negative control for the antibody used. Relative molecular weights are shown in kilodaltons and were determined by prestained molecular weight markers (Bio-Rad). The position of the putative nonphosphorylated (30 kD) IGFBP-1 species is indicated. Using densitometric analysis, we found the amounts of nonphosphorylated IGFBP-1 in the 2 normal samples to be 1.021 and 1.167, respectively, in arbitrary units; in the 2 PV patients, the amounts were found to be 2.897 and 3.115, respectively, whereas in the recombinant control, it was 1.067. The amounts of the phosphorylated IGFBP-1 species (28 kD) were 0.188 and 0.256 in the 2 normal subjects, respectively; in the 2 PV patients, they were 0.707 and 0.736, respectively, whereas in the recombinant control it was 0.292. The ligand blots confirm that the level of circulating IGFBP-1 in PV is greater than in normal.