Validation of a low-dose ACTH stimulation test in healthy adult horses

摘要

Objective-To determine the lowest ACTH dose that would induce a maximum increase in serum cortisol concentration in healthy adult horses and identify the time to peak cortisol concentration.Design-Evaluation study.Animals-8 healthy adult horses.Procedures-Saline (0.9% NaCl) solution or 1 of 4 doses (0.02, 0.1, 0.25, and 0.5 mu g/kg [0.009, 0.045, 0.114, and 0.227 mu g/lb]) of cosyntropin (synthetic ACTH) were administered IV (5 treatments/horse). Serum cortisol concentrations were measured before and 30, 60, 90, 120, 180, and 240 minutes after injection of cosyntropin or saline solution; CBCs were performed before and 30, 60, 120, and 240 minutes after injection.Results-For all 4 doses, serum cortisol concentration was significantly increased, compared with the baseline value, by 30 minutes after administration of cosyntropin; no significant differences were detected among maximum serum cortisol concentrations obtained in response to administration of doses of 0.1, 0.25, and 0.5 mu g/kg. Serum cortisol concentration peaked 30 minutes after administration of cosyntropin at a dose of 0.02 or 0.1 mu g/kg, with peak concentrations 1.5 and 1.9 times, respectively, the baseline concentration. Serum cortisol concentration peaked 90 minutes after administration of cosyntropin at a dose of 0.25 or 0.5 mu g/kg, with peak concentrations 2.0 and 2.3 times, respectively, the baseline concentration. Cosyntropin administration significantly affected WBC, neutrophil, and eosinophil counts and the neutrophil-to-lymphocyte ratio.Conclusions and Clinical Relevance-Results suggested that in healthy horses, administration of cosyntropin at a dose of 0.1 mu g/kg resulted in maximum adrenal stimulation, with peak cortisol concentration 30 minutes after cosyntropin administration. (J Am Vet Med Assoc 2011239:834-841)