Histopathological and immunohistochemical features of proliferative lesions in the pituitary pars distalis of rats

Abstract

Pituitary proliferative lesions derived from the endocrine cells of the pars distalis are frequently encountered and adenomas/carcinomas are a common cause of death in standard 2-year carcinogenicity studies using various rat strains, especially Sprague-Dawley. This report describes the immunohistochemical characteristics of pituitary tumors derived from the pars distalis in rats. Prolactin (PRL)-containing tumors are the most common, with PRL/growth hormone (GH) dual positive tumor masses (PRL/GH co-positive tumor masses) being more prevalent than only PRL-positive tumor masses (PRL single-positive tumor masses). GH-containing tumors are relatively numerous and many of these are also PRL/GH co-positive tumor masses. TSH-containing tumors are common in females. PRL-containing tumors have been shown to increase the incidence of hyperlactation in males and mammary adenomas/adenocarcinomas in females, suggesting that these masses are functional tumors.

Sonography of the pituitary gland in pet rats

“…We believe that our findings could help differentiate between normal and abnormal PG-size pituitary gland abnormalities, such as neoplasia or hyperplasia, could thus be identified as antemortem. 3 In clinical practice, the diagnosis of pituitary tumors is infrequent (8 rats out of 375 animals, according to an epidemiological study on pet rats 3 ), although a high incidence of these tumors in rats has been proven [3][4][5][6][7][8][9] ; consequently, our proposed method could help the clinician in the diagnostic process and increase the frequency of premortem diagnosis of these tumors. Species-specific ultrasound nor-mality ranges of the PG would facilitate the diagnosis of pituitary pathologies, which typically present with initial nonspecific neurological symptoms.…”

“…The proliferative lesions of the pars distalis in rats include focal hyperplasia, adenomas, and carcinomas 9 . The incidence of focal hyperplasia is higher in males than in females, whereas the incidence of adenomas and carcinomas is higher in females 9 .…”

“…9 The incidence of focal hyperplasia is higher in males than in females, whereas the incidence of adenomas and carcinomas is higher in females. 9 Pituitary adenomas are common in geriatric rats and in Sprague-Dawley and Fisher strains of rats with a prevalence of 85% and 83%, respectively. 10 Rat tumors of the PG's pars distalis mainly consist of prolactinproducing cells, which appear to have a lower incidence in ovariectomized rats.…”

“…The proliferative lesions of the pars distalis in rats include focal hyperplasia, adenomas, and carcinomas 9 . The incidence of focal hyperplasia is higher in males than in females, whereas the incidence of adenomas and carcinomas is higher in females 9 . Pituitary adenomas are common in geriatric rats and in Sprague–Dawley and Fisher strains of rats with a prevalence of 85% and 83%, respectively 10 …”

“…7 Many sources rank pituitary gland (PG) tumors, especially those in the pars distalis, as the most common endocrine tumor in rats and a common cause of death in rats over the age of two, especially females. 4,8,9 Contributing factors that have been suggested for pituitary tumor development are obesity and high protein or high-calorie diets. 2,5,10 The proliferative lesions of the pars distalis in rats include focal hyperplasia, adenomas, and carcinomas.…”