Immunoreactive Inhibinα-Subunit in Human Serum: Implications for Radioimmunoassay*

The specificity of the most widely used heterologous RIA for human serum inhibition was examined with regard to its cross-reactivity with the alpha-subunit of inhibin. Using a mixture of recombinant alpha inhibin proteins, including precursor and mature forms, the epitopic specificity of this antibody was localized entirely to the alpha-subunit. Furthermore, varying degrees of alpha inhibin immunoactivity were demonstrated in serum from normal subjects and patients with various reproductive disorders by both Western blot and RIA. These results demonstrate that data obtained using this RIA should be interpreted with caution as to the degree to which they reflect the presence of intact dimeric inhibin vs. alpha inhibin proteins in the circulation.