Biological Response Stability of Refrigerated Cosacthen after Opening and Non-Hormonal Effects of ACTH Stimulation Testing in Healthy Dogs

The adrenocorticotropic hormone stimulation test (ACTHST) is widely used to evaluate adrenal reserve in dogs. This study assessed the effects of refrigerated storage of tetracosactide (Cosacthen) after opening for up to three weeks and investigated hematological, biochemical, and electrolyte changes following ACTH stimulation. Ten healthy beagle dogs (five males and five females) were enrolled. Each dog received tetracosactide (5 μg/kg, IV) at vial opening (T0) and at 7-day intervals over 3 weeks (T1 to T3), using aliquots from the same vial stored at 2–8°C. Blood samples were collected before and 1 hour after ACTH administration to measure cortisol, hematology, biochemistry, and electrolytes. Clinical monitoring was performed after each test. Cortisol concentrations increased significantly after ACTH administration at all time points (T0–T3). Delta-cortisol was higher at T1 than at T0 (P = 0.0104) and lower at T2 than at T1 (P = 0.0059), with no differences among T0, T2, and T3. After ACTH administration, red blood cell count, hematocrit, hemoglobin, albumin, alkaline phosphatase, triglycerides, cholesterol, potassium, and total calcium decreased significantly, whereas glucose increased. All values remained within reference intervals, and no adverse effects were observed. Refrigerated storage of Cosacthen after opening did not alter cortisol responses. Post-ACTH changes in laboratory variables should be considered when interpreting results.