Adrenocortical function tests in dogs with hyperfunctioning adrenocortical tumours

The response has been studied in nine dogs with hyperadrenocorticism due to adrenocortical tumours to the administration of dexamethasone, insulin, lysine-vasopressin and tetracosactide by measuring the changes in plasma cortisol concentration. Administration of dexamethasone did not produce a decrease in the plasma concentration of cortisol in any of these dogs. Administration of insulin caused slight increases in the plasma concentration of cortisol in four out of eight dogs. Lysine-vasopressin increased the plasma concentration of cortisol in eight out of nine dogs, three responded supranomally. Eight out of the nine dogs responded to tetracosactide administration, three responded supranormally, It is concluded that in the dog, in contrast to man, the lysine-vasopressin test cannot be used to differentiate between pituitary-dependent hyperadrenocorticism and hyperadrenocorticism due to an adenocortical tumour. Apparently pituitary ACTH is not completely depleted in dogs with hyperfunctioning adrenocortical tumours.