Effect of trilostane and mitotane on aldosterone secretory reserve in dogs with pituitary-dependent hyperadrenocorticism.

Abstract

BACKGROUND: Maximal aldosterone secretion in healthy dogs occurs 30 minutes postadrenocorticotropin (ACTH; 5 μg/kg IV) stimulation. The effect of trilostane and mitotane on aldosterone at that time is unknown. OBJECTIVES: To assess the effect of trilostane and mitotane in dogs with pituitary-dependent hyperadrenocorticism on aldosterone secretory reserve. To determine if aldosterone concentration correlates with electrolyte concentrations. ANIMALS: Serum collected from 79 client-owned dogs and 33 stored samples. METHODS: Client-owned dogs had ACTH stimulation tests with cortisol concentrations measured at 0 and 60 minutes and aldosterone concentrations measured at 0, 30, and 60 minutes. Stored samples had aldosterone concentrations measured at 0 and 60 minutes. Ten historical clinically healthy controls were included. All had basal sodium and potassium concentrations measured. RESULTS: The aldosterone concentrations in the mitotane- and trilostane-treated dogs at 30 and 60 minutes post-ACTH were significantly lower than in clinically healthy dogs; no significant difference was detected in aldosterone concentration between 30 and 60 minutes in treated dogs. However, a significantly higher percentage of dogs had decreased aldosterone secretory reserve detected at 30 minutes than at 60 minutes. At 30 minutes, decreased secretory reserve was detected in 49% and 78% of trilostane- and mitotane-treated dogs, respectively. No correlation was detected between aldosterone and serum electrolyte concentrations. CONCLUSIONS AND CLINICAL IMPORTANCE: Decreased aldosterone secretory reserve is common in trilostane- and mitotane-treated dogs; it cannot be predicted by measurement of serum electrolyte concentrations. Aldosterone concentration at 30 minutes post-ACTH stimulation identifies more dogs with decreased aldosterone secretory reserve than conventional testing at 60 minutes.