Synthetic peptide immunocortin stimulates the production of 11-oxycorticosteroides by rat adrenal cortex through ACTH receptors

Abstract

Adrenocorticotropic hormone (ACTH)-like peptide immunocortin (IMC) VKKPGSSVKV, corresponding to the amino acid sequence 11-20 of the variable part of human immunoglobulin G (IgG) 1 heavy chain, at concentrations of 10(-9)-10(-6) I was found to increase the adenylate cyclase activity in adrenal cortex membranes, while intramuscular injection of immunocortin at doses of 10-100 microg/kg was found to stimulate the secretion of 11-oxycorticosteroids (CS) from the adrenals to the bloodstream. Immunocortin was labeled with tritium to specific activity of 22 Ci/mmol. Receptor binding studies revealed that [(3)H]immunocortin ([(3)H]IMC) bound with high affinity and specificity to ACTH receptors on rat adrenal cortex membranes (K(d)=2.1+/-0.2 nM, B(max)=1.1+/-0.1 pmol/mg protein).