THE COMBINED CORTICOTROPIN-RELEASING HORMONE LYSINE VASOPRESSIN TEST DISCLOSES A CORTICOTROPH PHENOTYPE

The combined administration of CRH and vasopressin to man now offers a powerful means to directly assess the pituitary corticotroph reserve. A double blind, randomized, placebo-controlled, cross-over trial offe red the opportunity to perform the combined CRH/lysine vasopressin (LV P) test (100 mu g ovine CRH, followed by 1 IU LVP over 15 min) on 3 di fferent occasions without treatment in 10 normal male subjects. We sho wed that peak ACTH plasma levels after stimulation had wide intersubje ct variation, whereas they were remarkably stable in a given individua l, with a mean intraclass correlation coefficient of 0.90 (95% confide nce limits, 0.74-0.96). Peak ACTH plasma levels after CRH/LVP administ ration were not significantly correlated with basal plasma cortisol le vels (r = -0.14; P > 0.45), but were strongly and inversely correlated with peak cortisol plasma levels after Cortrosyn stimulation (0.25 mg , im; r = -0.78; P < 0.0001). These data provide the first evidence th at the overall hypothalamic-pituitary-adrenocortical axis has an intri nsic activity that is constitutively fixed for a given individual. The power of the combined CRH/LVP test offers a unique means to measure a genuine corticotroph phenotype in each individual.