Pituitary gland changes in canine hypoadrenocorticism: a functional and immunocytochemical study.

Pituitary gland changes were evaluated immunocytochemically in three dogs with primary hypoadrenocorticism (HAC) and one dog with secondary HAC and related to the clinical, endocrinological and pathological findings. In primary HAC, the adrenocorticotrophic hormone (ACTH) immunoreactivity was increased in the pars distalis of the pituitary gland and all cortical layers of the adrenal gland were severely atrophied. This increase would be expected to reflect a high level of ACTH synthesis in the corticotrophs due to a lack of negative cortisol feed-back. In contrast, in the dog with secondary HAC the ACTH immunoreactivity was decreased in the pituitary gland, the basal plasma ACTH concentration was low and the zona fasciculata and reticularis were atrophied, but the zona glomerulosa was well preserved. These findings are consistent with a diminished synthesis of ACTH. Thus, pituitary gland changes differ in primary and secondary HAC and are consistent with the clinical, endocrinological and histopathological findings.