Immunocytochemical Demonstration of Proopiomelanocortin-derived Peptides in Pituitary Adenomas of the Pars Intermedia in Horses

Abstract

Abstract. Adenomas of the pars intermedia from 19 horses and normal pituitary glands from seven horses were evaluated histologically and immunocytochemically for adrenocorticotropic hormone (ACTH), a-melanocyte-stimulating hormone (a-MSH), &endorphin (@-END), proopiomelanocortin (POMC), prolactin, neuron specific enolase, and glial fibrillary acidic protein (GFAP). The 26 horses ranged in age from 7 to 31 years. Histologically, all adenomas had a uniform pattern characterized by cords of large columnar cells forming palisades and pseudoacini separated by a delicate fibrovascular stroma. Immunostaining of adenomas derived from the pars intermedia was similar to that of non-neoplastic equine pars intermedia. An immunocytochemical evaluation revealed a diffuse, strong cytoplasmic reaction for POMC, a moderate to strong reaction for a-MSH and (3-END, a weak reaction for ACTH, and negative immunostaining for prolactin, GFAP, and neuron specific enolase in the adenomas. The unique clinicopathologic syndrome that develops in horses with pituitary adenomas appears to be the result of an over-production of POMC-derived peptides in addition to space-occupying effects resulting in dysfunction of the hypothalamus and neurohypophysis.

Pituitary Lesions, Obesity, and Mesenteric Lipomas in Insulin-Resistant Horses

“…Although adrenal cortical hyperplasia is commonly associated with proliferative pituitary lesions in other species, it is uncommon in horses [10] [17]. Likewise, there was no association between pituitary score and adrenal corticomedullary ratio in the current study.…”

Tumors of the endocrine system in the horse - clinical pathology

“…Neuere Literaturangaben zeigen jedoch, dass das ECS mit geeigneten Testverfahren und verbesserter Information der Tierärzte sehr viel Tab. 2 Klinische und pathologische Befunde bei Pferden mit einem Adenom der PI (n=9) Clinical and pathological findings in horses with pars intermedia adenomas (n=9) w = weiblich; mk = männlich kastriert; J = Jahre; ECS = Equines Cushing Syndrom; WH = Wundheilung; PI = Pars intermedia; PCZ = Phäochromozytom; NN = Nebenniere; NNR = Nebennierenrinde; SD = Schilddrüse; ZNS = Zentralnervensystem häufiger diagnostiziert (Hoppen et al 2006) und auch bei jüngeren Tieren (Mindestalter 7 Jahre) erkannt wird (Heinrichs et al 1990). Infolge einer gestörten Synthese von Adrenokortikotropem Hormon (ACTH) in der erkrankten PI kommt es zu einer Erhöhung der adrenalen Kortisolsekretion, wobei diskutiert wird, dass a-Melanozyten-stimulierendes Hormon (aMSH) und b-Endorphin (bEnd) die Wirkung von ACTH potenzieren und somit zu einem weiteren Anstieg der adrenalen Kortisolproduktion führen, was dann die in Tabelle 1 aufgeführten klinischen Symptome und labormedizinischen Befunde erklärt.…”

A Case of a Pony with Cushing's Disease.

“…In this study, most cells in the pars Equine Cushing's disease (call it C's d throughout) is defined as pituitary-dependent hyperadrenocorticism [4]. There are many reports on equine C's d at overseas lands, which can present signs of hirsutilism, polydipsia, polyuria, diabetes insipidas, many secondary infections and muscle wasting, and may be associated with adenoma in the pars intermedia [1,3,6,8,11]. In Japan, however, little information is available on equine C's d. On race horses without any of these clinical signs, we have observed pituitary adenoma, which is characterized by an enlarged pars intermedia, showing the marked increase in number and size of adenocorticotropic hormone (ACTH) immunoreactive cells [9].…”

“…Immunolabelling was performed using antiserum to porcine ACTH (1:1,000) or to human β-endorphin (β-End) (1:1,600) produced in the rabbit. The other half of the pituitary gland was dissected into 1 mm 3 blocks of the pars intermedia after fixing in 10% neutral buffered formalin. The blocks were post-fixed in 1% osmium tetroxide for 1.5 hr, dehydrated in a graded series of alcohol solutions, and embedded in Epon-Araldite.…”

“…Heinrichs et al [3] reported that cells in the pars intermedia in normal horses secrete peptide hormones ( A C T H , β -E n d , α -M S H e t c . ) d e r i v e d f r o m proopiomelanocortin.…”