Vasopressin stimulation testing in hospitalized foals.

AVP stimulation testing reveals HPAA dysfunction severity in foals, with septic foals showing the most attenuated ACTH and cortisol responses.

This prospective, observational case-control study evaluated hypothalamic-pituitary-adrenal axis (HPAA) function in 60 foals (15 healthy controls, 19 septic, and 26 sick non-septic [SNS]) using an arginine vasopressin (AVP) stimulation test. Foals received 5 IU of AVP, and corticotropin-releasing hormone (CRH), ACTH, and cortisol concentrations were measured at 0, 15, 30, 60, and 90 minutes. All groups demonstrated measurable ACTH and cortisol increases at 15 and 30 minutes post-administration. However, ACTH concentrations at 15 minutes were significantly lower in both septic and SNS foals compared to healthy controls. The fold increase in ACTH was most attenuated in septic foals compared to both SNS and healthy foals, and the fold increase in cortisol was significantly lower in septic foals versus healthy controls. These findings indicate that HPAA dysfunction correlates with disease severity, being most pronounced in septic foals. The AVP stimulation test successfully differentiated healthy foals from ill foals and stratified disease severity within hospitalized populations. The authors suggest this test may serve as a clinically useful tool to identify HPAA dysfunction—potentially guiding therapeutic decisions such as glucocorticoid supplementation—in critically ill neonatal foals. Further studies are warranted to determine specific treatment thresholds and evaluate outcomes associated with test-guided interventions.

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