Immunoreactive Insulin-Like Growth Factor I (IGF-I) and IGF-I-Binding Protein Content in Human Thyroid Tissue*

We measured immunoreactive insulin-like growth factor I (IGF-I) in extracts of normal and nodular thyroid tissue obtained at surgery from patients with nontoxic goiter. The nodular tissues contained a higher concentration [mean, 279.0 ± 69.7 (±se) mU/g] than paired normal tissues (115.5 ± 17.9 mU/g; P = 0.024; n = 12); a difference was evident in all but one patient. Sephadex G-50 gel filtration of tissue extracts revealed two immunoreactive peaks, the first in the void volume of the column, and the second in the elution volume of authentic IGF-I. The first peak was identified as IGF-I-binding protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after cross-linking with iodinated IGF-I. Isolated thyroid cell membranes contained high affinity IGF-I-binding sites of similar affinity and numbers in both normal and nodular thyroid tissue. The IGF-I content of six thyroid cancer extracts was higher than that of normal thyroid tissue, but the IGF-I content of thyroid tissue from six patients wit...