Immunocytochemical study of the hypophysis in 25 dogs with pituitary-dependent hyperadrenocorticism

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Abstract
Pituitary adenomas were found in 21 (84%) of 25 dogs with spontaneous pituitary-dependent hyperadrenocorticism. Six dogs had pars intermedia adenomas, whereas 15 had tumors of the pars distalis. Diffuse corticotroph cell hyperplasia was found in 1 of the 4 pituitaries without adenoma; in 2 dogs with pituitary adenoma, coexisting hyperplasia of the surrounding corticotrophs was also present. Immunocytochemical staining of the pituitaries revealed positive staining for ACTH, .beta.-lipotropin and .beta.-endorphin in the majority of pars distalis and pars intermedia adenomas. The most frequent and intense staining was found with anti-.beta.-endorphin. In most pars intermedia tumors, many cells stained strongly for .alpha.-MSH; double immunostaining of 1 pars intermedia adenoma for ACTH and .alpha.-MSH showed that some tumor cells stained only for ACTH or .alpha.-MSH; others contained both peptides. Only occasional cells stained for .alpha.-MSH in pars distalis adenomas.