Corticosterone plasma concentration in male mule ducks: effects of sampling sites, repeated samplings and ACTH injections

1. Changes in plasma corticosterone concentrations according to puncture si tes and various challenges including injections of an ACTH agonist (Immedia te Synacthen) were investigated in male mule ducks. 2. Lower concentrations were measured in samples drawn by puncture from the occipital sinus than at a wing vein site. 3. Immobilisation and a single intramuscular injection of saline solution ( 1 ml, 0.9%) had no effect on plasma corticosterone after 15 min. 4. A single intramuscular injection of ACTH (5 mu g/kg body weight) produce d a rise (P<0.05) in corticosterone. Maximum concentrations were measured a fter 10 min and, in the absence of further sampling, a return to initial le vels was observed by 1 h. 5. On the other hand, repeated bleedings following ACTH challenge maintaine d higher corticosterone concentrations. 6. A single intramuscular injection of ACTH at doses ranging between 0.625 to 20 mu g/kg body weight increased corticosterone concentrations (P<0.05) in a dose-dependent manner, with the responses plateauing at doses of 1.25 mu g/kg and higher.