1997 Volume 59 Issue 8 Pages 707-710
The pars intermedia of the pituitary gland, and plasma ACTH and cortisol levels in the pony, which was first diagnosed in Japan as indicating equine Cushing's disease, were examined by immunohistochemistry and radioimmunoassay, respectively. The pars intermedia was greatly enlarged and most of its cells were immunoreactive for antisera to both adenocorticotropic hormone (ACTH) and β-endorphin (β-End). The plasma ACTH level was elevated when clinical symptoms appeared. The present results reveal that equine Cushing's disease in this pony was induced by the hypersecretion of ACTH and β-End from the enlarged pars intermedia of the pituitary gland.