Estimation of Somatomedin-C Levels in Normals and Patients with Pituitary Disease by Radioimmunoassay

TLDR

A radioimmunoassay for somatomedin‑C enables discrimination of its serum concentration from related peptides, improving upon less specific bioassays. Rabbits were immunized with a somatomedin‑C–ovalbumin conjugate to generate specific antibodies. The assay is highly specific: it does not detect most peptide hormones up to 1 µM, insulin cross‑reacts only at >0.1 µM, somatomedin‑A is 3 % as active, cloned rat liver activity does not bind, and it can quantify somatomedin‑C in sera of many subhuman species.

Abstract

The development of a radioimmunoassay for somatomedin-C has for the first time made it possible to discriminate between serum concentrations of a single peptide or closely related group of peptides and the net somatomedin activity measured by less specific bioassay and radioreceptor techniques. Antibodies to human somatomedin-C were raised in rabbits using a somatomedin-C ovalbumin complex as the antigen. A variety of peptide hormones at concentrations up to 1 μM are not recognized by the antibody. Insulin at concentrations >0.1 μM cross reacts in a non-parallel fashion; purified somatomedin-A is only 3% as active as somatomedin-C; and radiolabeled cloned rat liver multiplication stimulating activity does not bind to the antibody. Immunoreactive somatomedin-C can also be quantitated in the sera of a variety of subhuman species.