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

Objective-To determine whether low doses of synthetic ACTH could induce a m aximal cortisol response in clinically normal dogs and to compare a low-dos e ACTH stimulation protocol to a standard high-dose ACTH stimulation protoc ol in dogs with hyperadrenocorticism. Design-Cohort study. Animals-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 mu g/kg [0.45, 2.3, or 4.5 mu g/lb] of body weight, IV) in ra ndom order at 2-week intervals. Samples for determination of plasma cortiso l and ACTH concentrations were obtained before and 30, 60, 90, and 120 minu tes after ACTH administration. Each dog with hyperadrenocorticism was given 2 doses of cosyntropin [5 mu g/kg or 250 mu g/dog) in random order at 2-we ek intervals. In these dogs, samples for determination of plasma cortisol c oncentrations 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 amon g the 3 doses. However, mean plasma cortisol concentration in dogs given 1 mu g/kg peaked at 60 minutes, whereas dogs given doses of 5 or 10 mu g/kg h ad peak cortisol values at 90 minutes. In dogs with hyperadrenocorticism, s ignificant differences were not detected between cortisol concentrations af ter administration of the low or high dose of cosyntropin. Clinical Implications-Administration of cosyntropin at a rate of 5 mu g/kg resulted in maximal stimulation of the adrenal cortex in clinically normal dogs and dogs with hyperadrenocorticism.