Cortisol and adrenocorticotropic hormone concentrations in horses with systemic inflammatory response syndrome

Background Plasma adrenocorticotropic hormone (ACTH) and serum cortisol concentrations increase with illness‐associated stress. Dynamics of plasma ACTH and serum cortisol concentrations in adult horses with systemic illness are undocumented. Hypothesis/Objective To determine whether ACTH and cortisol concentrations and the ACTH/cortisol ratio vary with survival, the presence of systemic inflammatory response syndrome (SIRS), or ischemic gastrointestinal lesions at admission, or throughout hospitalization. Animals One hundred fifty‐one adult horses. Methods Prospective study measuring serum cortisol and plasma ACTH at admission and on days 2, 4, and 6 of hospitalization. Horses were grouped by outcome (survival, SIRS status, number of SIRS criteria [SIRS score], SIRS severity group, and the presence of an ischemic lesion). Differences between groups and over time for ACTH, cortisol, and ACTH/cortisol ratio were investigated with a mixed effect model. Receiving operator characteristic curves and odds ratios were calculated for survival and ischemia. Results In all groups, ACTH, cortisol, and ACTH/cortisol ratio significantly decreased over time ( P  < .0001). ACTH, cortisol, and ACTH/cortisol ratio were higher at admission in nonsurvivors, and ACTH and cortisol were higher in horses with ischemic lesions ( P  < .01). Horses with ACTH above reference interval at admission were 6.10 (2.73‐13.68 [95% confidence interval]) times less likely to survive ( P  < .0001). No significant difference in ACTH, cortisol, and ACTH/cortisol ratio between horses with different SIRS status, scores, or groups were detected, although nonsurvivors had a higher SIRS score ( P  < .0001). Conclusions and Clinical Importance Pituitary and adrenal responses are altered in nonsurviving horses and those with an ischemic gastrointestinal lesion.