The hypothalamic-pituitary-adrenal axis response to ovine corticotropin-releasing-hormone stimulation tests in healthy and hospitalized foals.

Abstract

The hypothalamic-pituitary-adrenocortical axis (HPAA) response to sepsis can be impaired in critical illness. Corticotropin-releasing hormone (CRH) stimulation test might assess HPAA function in foals. To evaluate plasma cortisol, ACTH, arginine vasopressin (AVP), and endogenous CRH (eCRH) response to different doses of ovine CRH (oCRH). Healthy (n=14) and hospitalized (n=15) foals <7 days of age. In this prospective randomized study, oCRH (0.1, 0.3, and 1μg/kg) was administered intravenously and blood samples were collected before, 15, 30, 60, and 90 minutes after administration of oCRH to determine plasma hormone concentrations. The hormonal response was evaluated as the difference (Delta; μg/dL or pg/mL) or percent change between baseline hormone concentration and each time point after oCRH stimulation. Cortisol concentrations increased from baseline at 15 minutes with 0.1 and 0.3μg/kg and at 30 and 60 minutes from baseline with 1μg/kg oCRH (P < .05) in healthy and hospitalized foals. ACTH concentrations increased from baseline at 15 minutes with 0.1μg/kg and at 30 minutes with 1μg/kg oCRH (P < .05) in hospitalized foals. Delta cortisol 0 - 30, ACTH 0 - 30, and eCRH 0 - 30 was higher for the 1μg/kg compared with 0.1μg/kg oCRH in healthy foals (P < .05). Delta ACTH 0 - 15 and eCRH 0 - 30 was higher for the 1μg/kg compared with the lower doses of oCRH in hospitalized foals (P < .05). Cortisol, ACTH, and eCRH concentrations increased in response to administration of all doses of oCRH. One microgram per kilogram of oCRH appears to be optimal for the assessment of HPAA in healthy and hospitalized foals.