ROMERO, L.M.*; RICH, E.L.; TRAN, K.D.; NEPHEW, B.C.: Regulation of Corticosterone Release in Captive House Sparrows

Earlier studies indicate that captive house sparrows (Passer domesticus) show both a daily rhythm in corticosterone release as well as a decrease in their corticosterone response to stress during their prebasic molt. We tested whether the capacity of the adrenal gland to release corticosterone changes during the daily cycle in captive house sparrows held under three conditions: on a short day photoperiod (11 L: 13 D); on a long day photoperiod (19 L: 5 D); and on a long day photoperiod while undergoing a prebasic molt. Basal corticosterone concentrations were collected within 3 min of entering the experimental room at two times of the day – several hours after lights on and at night. All birds under all conditions increased their corticosterone concentrations after 30 min of handling and restraint. Exogenous ACTH further augmented this response during both day and night in sparrows held under short and long day photoperiods, but was ineffective during molt. We further tested for changes in pituitary capacity to secrete ACTH by injecting exogenous ovine CRF, arginine vasotocin, or the two hormones together, and measuring subsequent corticosterone release. These ACTH releasing factors were ineffective under all conditions. In conclusion, the downregulation of corticosterone release during molt in captive house sparrows appears to be regulated primarily by decreasing the corticosterone secretory capacity of the adrenal tissue, and not at sites higher up in the Hypothalamic-Pituitary-Adrenal axis.