HYPERRESPONSIVENESS TO LYSINE-VASOPRESSIN IN CUSHING'S DISEASE
ABSTRACT The lysine-8-vasopressin (LVP)-test was performed in 11 normal subjects, with pituitary-dependent Cushing's disease and in 3 cases of Cushing's syndrome due to an adrenocortical carcinoma. The plasma 17-hydroxycorticosteroids response to LVP in Cushing's disease was compared with the response of the normal controls. It is concluded that patients with pituitary-dependent Cushing's syndrome are hyper-responsive to LVP. The possible mechanisms of this hyper-responsiveness are discussed: release of ACTH from the pituitary and/or an increased release of cortisol from the hyperplastic adrenals may occur. As expected, patients with Cushing's syndrome due to an adrenocortical carcinoma did not respond to LVP. It is suggested that the LVP-test can be used for the diagnosis of Cushing's syndrome and for the differential diagnosis between Cushing's disease and Cushing's syndrome due to an adrenocortical carcinoma, although it is recognized that in some cases this test will not be adequate.