PLASMA-CORTISOL RESPONSES TO REMOTE ADRENOCORTICOTROPIC HORMONE (ACTH) INFUSION IN FREE-RANGING RED DEER (CERVUS-ELAPHUS)

A remote infusion and blood collection device (Dracpac) was used on fr ee-ranging red deer stags to deliver i.v. a range of ACTH(1-24) doses and collect blood for cortisol determination. In Experiment 1, conduct ed in September, saline and 1, 4, and 16 IU ACTH/100 kg bodyweight wer e infused (n = 5-7 per treatment). In Experiment 2 (November), 16 and 64 IU ACTH/100 kg were infused (n = 5 per treatment); and the response of animals to restraint was also assessed (n = 6). Pre-infusion conce ntrations of plasma cortisol were low (mean 6.5 +/- 1.0 ng/ml), and un affected by infusion of saline. ACTH significantly elevated plasma cor tisol concentrations, with mean peak concentrations occurring 20-40 mi n postinfusion. Duration of the response was dose dependent, ranging f rom 80-160 min. With increasing doses of ACTH, maximal peak heights pl ateaued at approximately 40 and 60 ng/ml in September and November, re spectively; whereas the areas under the curves tended to increase. The minimum dose of ACTH that resulted in a maximal peak cortisol respons e was 4 IU. The maximum peak height of the cortisol response to 16 IU tended to be higher (P < 0.10) in November compared with September, su ggesting that adrenal responsiveness may change over this period. The adrenal response to a 16-IU ACTH challenge in Experiment 2 resulted in similar plasma cortisol concentrations to an acute stress event (rest raint). Four IU/100 kg ACTH i.v. is recommended as an appropriate dose for ACTH infusion studies in red deer stags. When used in conjunction with the Dracpac technique, it becomes a stress-free, repeatable proc edure for assessing aspects of adrenal cortex physiology in free-rangi ng deer. (C) Elsevier Science Inc. 1997.