127 Temporal changes in plasma and hair cortisol and leukocyte activity following ACTH treatment in cattle.

Abstract The objectives of this study were to: (1) determine the magnitude of circulating cortisol increase following administration of adrenocorticotropic hormone (ACTH; 100 IU) every 12 hours for 7 days; (2) assess how soon after the beginning of ACTH treatment an increase in hair cortisol can be detected; and (3) evaluate the immune response to ACTH treatment. Nonpregnant, nonlactating Holstein cows were assigned to one of two treatment groups: Control (n=12), receiving 2 mL of saline intramuscularly every 12 hours from day 0 to 6, or ACTH (n=12), receiving 100 IU ACTH (2 mL) intramuscularly every 12 hours from day 0 to 6. Blood samples were collected twice daily from days 0 to 7, once daily from days 8 to 14, and on days 21, 28, 35, 42, and 49. Additionally, intensive blood sampling every 2 hours was conducted on days 0, 3, and 6 to characterize cortisol concentration profiles. Weekly assessments included leukocyte cell counts, serum haptoglobin concentrations, neutrophil phagocytosis capacity, oxidative burst, and L-selectin (CD62L) expression. Tail-switch hair samples were collected weekly to measure hair cortisol concentrations. Cortisol levels were analyzed by ELISA, leukocyte counts by a hematology analyzer, neutrophil function and CD62L expression by flow cytometry, and haptoglobin levels by a colorimetric method. Data were analyzed using ANOVA with a repeated measures model. ACTH treatment significantly increased (P < 0.01) circulating cortisol concentrations on days 0 (13.8 ±2.1 vs. 1.8 ±0.3 ng/mL), 3 (22.0 ±2.0 vs. 1.6 ±0.1 ng/mL), and 6 (15.5 ±1.5 vs. 1.4 ±0.1 ng/mL) compared to the control. Hair cortisol concentrations increased (P < 0.01) by day 14 (24.0 ±1.1 vs. 6.7 ±0.9 pg/mg) and day 21 (11.5 ±5.3 vs. 5.3 ±0.8 pg/mg) following ACTH treatment but showed no differences (P > 0.20) on days 28, 35, 42, or 49. Total circulating leukocyte counts increased on day 7 (P < 0.01), primarily driven by neutrophilia (5.4 ±0.2 vs. 1.7 ±0.2 million cells/mL; P < 0.01). Lymphocyte counts tended to decrease (P = 0.10) from days 7 to 28 post-treatment. Neutrophil CD62L expression decreased on day 7 (10.0 ±0.08 vs. 10.6 ±0.09; P < 0.01), while lymphocyte CD62L expression increased (P < 0.01) on days 7 (8.4 ±0.1 vs. 8.1 ±0.1) and 14 (8.6 ±0.1 vs. 8.1 ±0.1). No significant differences were observed in neutrophil phagocytic capacity (P = 0.83) or oxidative burst (P = 0.32). Serum haptoglobin concentrations were increased (P = 0.05) only on day 7 (0.60 ±0.06 vs. 0.44 ±0.05). In conclusion, ACTH treatment effectively elevates cortisol concentrations, induces immune alterations, and leads to a detectable increase in tail-hair cortisol 14 days after the initial rise in circulating cortisol.