Plasma cortisol responses to three corticotrophic preparations in normal dogs

To compare cortisol responses to three corticotrophic preparations in normal dogs.

Eight clinically normal dogs (four intact males, four intact females) of medium size.

Each dog received four treatments on four separate occasions in a duplicated Latin square pattern. Treatments were two adrenocorticotrophin (ACTH) preparations given intramuscularly at 2.2 U/kg, one of the ACTH preparations given intramuscularly at 1 U/kg and a synthetic polypeptide with ACTH-like activity (tetracosactrin, cosyntropin) given intravenously at 5 micrograms/kg. Plasma samples were taken for cortisol assay before and at 0.5, 1, 2 and 4 h after treatment.

Plasma cortisol concentrations were similar with the two ACTH preparations and at both dose rates. Tetracosactrin produced smaller mean peak cortisol concentrations, which tended to occur earlier than with ACTH, and smaller values for the area under the curve of plasma cortisol concentration from zero time to 4 h.

The findings suggest that canine adrenal function can be tested adequately by giving ACTH intramuscularly at 1 U/kg and measuring plasma cortisol in samples taken at 0 and 2 h, or by giving tetracosactrin intravenously at 5 micrograms/kg and determining cortisol concentration at 0 and 1 h.