Assessment of the hypothalamic-pituitary-adrenocortical axis function using a vasopressin stimulation test in neonatal foals

Abstract

Background: Bacterial sepsis is the leading cause of death in foals and is associated with hypothalamic-pituitary-adrenocortical axis (HPAA) dysfunction. HPAA function can be evaluated by an arginine-vasopressin (AVP) stimulation test. Hypotheses/Objectives: Administration of AVP will stimulate a dose-dependent rise in systemic adrenocorticotropin-releasing hormone (ACTH) and cortisol in neonatal foals. There will be no response seen in corticotropin-releasing hormone (CRH) and baseline AVP will be within reference interval. Animals: Twelve neonatal foals, <72 hours old. Methods: HPAA function was assessed in foals utilizing 3 doses of AVP (2.5, 5, and 7.5 IU), administered between 24 and 48 hours of age in this randomized cross-over study. Cortisol, ACTH, CRH and AVP were measured at 0 (baseline), 15, 30, 60 and 90 minutes after AVP administration with immunoassays. The fold increase in cortisol and ACTH was calculated at 15 and 30 minutes compared to baseline. Results: All doses of AVP resulted in a significant increase in cortisol concentration over time, and a dose-dependent increase in ACTH concentration over time. ACTH and cortisol were significantly increased at 15 and 30 minutes, respectively after all 3 doses of AVP compared to baseline (P