Pituitary corticotropin-inhibiting peptide: properties and use in study of corticotropin action

Abstract

The biological properties of the naturally occurring pituitary peptide α_h⁷⁻³⁸-adrenocorticotropin (ACTH) have been investigated. α_h⁷⁻³⁸-ACTH is devoid of steroidogenic activity but inhibits competitively ACTH-induced steroidogenesis in vitro as well as in vivo. The long-term actions of ACTH on normal and tumor adrenal cells in culture are also antagonized by α_h⁷⁻³⁸-ACTH. The apparent K_i for the inhibition of cyclic AMP production by α_h⁷⁻³⁸-ACTH (301±62 nM) was significantly higher than the apparent K_i for the inhibition of corticosterone synthesis (21.6±6.8 nM). Analysis of the inhibition of ACTH-induced steroidogenesis and cyclic AMP production in normal rat adrenocortical cells indicates that two separate receptors may be involved in mediating these responses.