An alternative method for delivering adrenocorticotropin hormone in birds

In birds, intrajugular injection (i.j.) of exogenous adrenocorticotropin hormone (ACTH) has been used to challenge adrenocortical tissue when investigating various dynamics of the hypothalamic-pituitary-adrenal (HPA) axis. Although this method has been shown to deliver ACTH efficiently, i.j. injection can be difficult and potentially damaging to the bird, especially to young birds and small species. Intramuscular (i.m.) injection has been shown to be an alternative method for delivering ACTH to large birds; however, small songbirds have relatively less muscle mass in which to absorb i.m. injections and, in very small birds, even small needles may injure the delicate muscle tissue. Therefore, intraperitoneal (i.p.) administration of ACTH was investigated as a means of avoiding the potential problems associated with i.j. and i.m. injections when conducting adrenocortical pathway studies on small birds. Dark-eyed Juncos, Junco hyemalis, were first treated with dexamethasone to suppress the endogenous signal cascade for corticosterone release. Twelve hours later, birds were sampled for baseline corticosterone concentration and then immediately given an i.p. injection of either ACTH or physiological saline. A second blood sample was taken from all birds 30 min later to assess the effectiveness of i.p. ACTH administration on adrenocortical tissue. While saline-treated birds showed no significant increase in endogenous plasma corticosterone in response to the capture and handling protocol, ACTH-treated birds showed a significant increase in plasma corticosterone concentration, illustrating the effectiveness of the i.p. administration of exogenous ACTH. The adrenocortical response of ACTH-treated birds was similar in magnitude and rate of increase to that found in free-living, noninjected Juncos. Intraperitoneal injection of ACTH is thus a valid alternative to i.j. and i.m. injections when challenging adrenocortical tissue in small birds.