A monoclonal anti-peptide antibody mimics adrenocorticotropic hormone activity

A monoclonal antibody that specifically recognizes the adrenocorticotropic receptor (ACTH) on rat adrenal cells was tested for hormonal activity. The antibody behaved as an agonist based on three different biological activities associated with ACTH. An antibody concentration of 16 micrograms/ml stimulated isolated rat adrenal cells to secrete 800 ng/10(4) cells of corticosterone with a concomitant 10-fold increase of cAMP to 30 pmol/10(5) cells. Antibody concentrations above 16 micrograms/ml inhibited mitotic activity in mouse Y-1 adrenal cells. A radio-immunoassay using an anti-ACTH antibody showed that the monoclonal anti-adrenocorticotropic receptor antibody and ACTH are antigenically related. These findings suggest that the anti-receptor antibody recognizes the ligand binding domain of the ACTH receptor.