The effect of an injection of corticotrophin on plasma concentrations of corticosterone, growth hormone and prolactin in two strains of domestic fowl.

1. Three-week-old Light Sussex (LS) and Rhode Island Red (RIR) chicks were injected with long-acting corticotrophin (ACTH: 30 IU/kg) and the plasma concentrations of corticosterone, growth hormone (GH) and prolactin were determined over a 6-h period. Plasma concentrations of corticosterone and growth hormone were also measured after an injection of corticosterone (500 microgram/kg). 2. The resting plasma concentration of corticosterone in LS was less than that in RIR birds. The increase elicited by ACTH was smaller in LS but, since it was maintained for longer, the plasma corticosterone response was at least 18% larger than that in RIR birds. 3. Plasma GH concentration was decreased after an injection of ACTH in both strains but the decrease lasted longer in the LS chicks. 4. Plasma prolactin concentration was unaffected by ACTH. 5. After intra-abdominal injection of corticosterone, plasma GH concentration was depressed in both strains. It is concluded that ACTH-induced depression of plasma GH and growth is mediated by corticosterone.