Plasma concentrations of glucocorticoids in white-tailed deer: the effect of acute ACTH and dexamethasone administration

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Abstract
To study the response of the adrenal gland of white-tailed deer to exogenous ACTH, eight penned animals (five mature intact males, one mature castrate male, one adult castrate female, and one immature female) were sedated with xylazine and ketamine and then challenged with various doses of ACTH with and without dexamethasone (DX) pretreatment. Plasma concentrations of cortisol and cortiscosterone were determined by radioimmunoassay in serial samples taken from a jugular cannula. Rapid, dose-dependent increases lasting over 5 h were observed after intramuscular injection of 10, 20, or 40 IU of porcine ACTH. The ratio of cortisol to corticosterone varied from 2:1 to 40:1. Maximum cortisol concentrations averaged 14.9, 20.3, and 21.3 μg/dL, respectively. Intravenous infusion of 5 mg of DX induced a rapid decline of cortisol levels. Administration of 20 or 40 IU of ACTH 140 min after DX caused increases of cortisol which were not different from those when ACTH was given alone. It was concluded that (i) xylazine and ketamine immobilization is suitable for study of the adrenal activity in deer, (ii) 20 IU of ACTH elicits maximal response of cortisol and corticosterone, (iii) DX pretreatment can result in minimal cortisol concentrations but its use is not essential for studies of adrenal response to ACTH, and (iv) the adrenal response to ACTH of females and castrate males is similar to that of intact males.
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