Isolated Adrenal Cortex Cells: ACTH 4-23 (NH 2 ),ACTH 5-24,ACTH 6-24 and ACTH 7-23 (NH 2 );Cyclic AMP and Corticosterone Production 1

Summary

Suspensions of isolated adrenal cortex cells of the rat respond to the addition of ACTH_1-24 and related peptides with production of cAMP and corticosterone. A concentration of ACTH_1-24 which results in less than 20% of maximum cAMP production induces near-maximum corticosterone production; a concentration which results in 1-3% cAMP production induces 50% of maximum corticosterone production. ACTH_4-23(NH₂) and ACTH_5-24 are less potent than AC TH_1-24, but induce the same maximum corticosterone production (B _max) as ACTH_1-24; ACTH_6-24 induces a maximum equal to 0.4 of B _max; ACTH_7-23(NH₂) is inactive. AC TH_4-23(NH₂), ACTH_5-24 and ACTH_6-24 induce 0.86, 0.45 and 0.01 of the maximum cAMP production characteristic of AC TH_1-24; respectively; ACTH_7-23(NH₂) is inactive. ACTH_7-23(NH₂) is a competitive antagonist and shifts the ACTH_1-24 log concentration curves for cyclic AMP and for corticostemne to the same degree. These observations are discussed in terms of a dual receptor model and in terms of a single site-receptor reserve model.

The authors thank Mary Vegh for excellent technical assistance.