ACTH and cortisol concentration-time plots in healthy subjects exposed to different exogenous ACTH secretagogues (CRH, AVP, CRH and AVP, saline). Peptides were infused between 90 and 690 min after the start of blood sampling, as indicated by the dashed vertical lines. Arrows indicate the hormone or combination infused continuously. After 690 min, the heterologous peptide was injected by bolus. During saline infusion, both ACTH and cortisol show the expected circadian rise overnight.