An alternative method for delivering adrenocorticotropin hormone in birds

In birds, intrajugular injection (ij) of exogenous adrenocorticotropin horm one (ACTH) has been used to challenge adrenocortical tissue when investigat ing various dynamics of the hypothalamic-pituitary-adrenal (HPA) axis. Alth ough this method has been shown to deliver ACTH efficiently, ij injection c an be difficult and potentially damaging to the bird, especially to young b irds and small species. Intramuscular (im) injection has been shown to be a n alternative method for delivering ACTH to large birds; however, small son gbirds have relatively less muscle mass in which to absorb im injections an d, in very small birds, even small needles may injure the delicate muscle t issue. Therefore, intraperitoneal (ip) administration of ACTH was investiga ted as a means of avoiding the potential problems associated with ii and im injections when conducting adrenocortical pathway studies on small birds. Dark-eyed Juncos,Junco hyemalis, were first treated with dexamethasone to s uppress the endogenous signal cascade for corticosterone release. Twelve ho urs later, birds were sampled for baseline corticosterone concentration and then immediately given an ip injection of either ACTH or physiological sal ine. A second blood sample was taken from all birds 30 min later to assess the effectiveness of ip ACTH administration on adrenocortical tissue. While saline-treated birds showed no significant increase in endogenous plasma c orticosterone in response to the capture and handling protocol, ACTH-treate d birds showed a significant increase in plasma corticosterone concentratio n, illustrating the effectiveness of the ip administration of exogenous ACT H. The adrenocortical response of ACTH-treated birds was similar in magnitu de and rate of increase to that found in free-living, noninjected Juncos. I ntraperitoneal injection of ACTH is thus a valid alternative to ii and im i njections when challenging adrenocortical tissue in small birds. (C) 2001 A cademic Press.