Evaluation of a low-dose synthetic adrenocorticotropic hormone stimulation test in clinically normal dogs and dogs with naturally developing hyperadrenocorticism

Abstract

Objective To determine whether low doses of synthetic ACTH could induce a maximal cortisol response in clinically normal dogs and to compare a low-dose ACTH stimulation protocol to a standard high-dose ACTH stimulation protocol in dogs with hyperadreno-corticism. Design Cohort study. Animats 6 clinically normal dogs and 7 dogs with hyperadrenocorticism. Procedure Each clinically normal dog was given 1 of 3 doses of cosyntropin (1, 5, or 10 μg/kg [0.45, 2.3, or 4.5 μg/lb] of body weight, IV) in random order at 2-week intervals. Samples for determination of plasma cortisol and ACTH concentrations were obtained before and 30, 60, 90, and 120 minutes after ACTH administration. Each dog with hyperadrenocorticism was given 2 doses of cosyntropin (5 μg/kg or 250 μg/dog) in random order at 2-week intervals. In these dogs, samples for determination of plasma cortisol concentrations were obtained before and 60 minutes after ACTH administration. Results In the clinically normal dogs, peak cortisol concentration and area under the plasma cortisol response curve did not differ significantly among the 3 doses. However, mean plasma cortisol concentration in dogs given 1 μg/kg peaked at 60 minutes, whereas dogs given doses of 5 or 10 μg/kg had peak cortisol values at 90 minutes. In dogs with hyperadrenocorticism, significant differences were not detected between cortisol concentrations after administration of the low or high dose of cosyntropin. Ctinical Implications Administration of cosyntropin at a rate of 5 μg/kg resulted in maximal stimulation of the adrenal cortex in clinically normal dogs and dogs with hyperadrenocorticism. (J Am Vet Med Assoc 1999;214:1497-1501)