Major hypercorticism is an endocrine feature of ewes with naturally occurring scrapie

The aim of this study was to identify the origin of scrapie-induced hyperco rtisolism. Cortisol and ACTH kinetics and production rate were measured in 14 ewes (6 healthy and 8 scrapie-affected). It was shown that cortisol plas ma clearance remained unmodified but that cortisol production rate and plas ma concentrations of free cortisol were increased by a factor of 5, whereas the total cortisol plasma concentrations were only doubled. The apparent d iscrepancy between adrenal secretion rate and the corresponding total corti sol plasma levels was attributable to the scrapie-induced lower corticoster oid-binding globulin (CBG) binding capacity, which altered the ratio of fre e-to-bound cortisol. The secretion rate of ACTH from diseased ewes was incr eased by a factor of 1.5, in comparison with healthy ewes, and 4 of the 8 s crapie-affected ewes exhibited a decreased response to a low dexamethasone suppression test. The administration of tetracosactide induced a a-fold inc rease in the cortisol production in diseased ewes, compared with that of he althy ewes, but the pituitary sensitivity to ovine CRF was not modified by the prion disease. In conclusion, natural scrapie displays a syndrome of hypercorticism associ ated with increased ACTH secretion, hyperresponsiveness of the adrenals, an d lower CBG binding capacity, which leads to overexposure to CBG-free corti sol.