Spontaneous lesions in endocrine glands of experimental Wistar rats and beagle dogs

A retrospective analysis was undertaken at Zydus Research Centre to understand the incidences of spontaneous lesions in endocrine glands of Wistar rats and beagle dogs. The data from a total of 841 Wistar rats (418 males and 423 females) and 144 beagle dogs (72 males and 72 females) was used from placebo/vehicle treated control group of different non-clinical toxicity studies. The lesions in various endocrine glands were classified according to the species and age of the animals at termination of study. Among the endocrine glands, the highest numbers (types) of spontaneous lesions were observed in adrenal glands followed in descending order by pituitary, thyroid, endocrine pancreas and parathyroid glands in Wistar rats. In beagle dogs, highest numbers (types) of spontaneous lesions were seen in adrenals followed by thyroid, endocrine pancreas, pituitary and parathyroid gland. In adrenal glands of Wistar rats, the incidences of cortical cell vacuolation, hemorrhages and hemangiectasis/peliosis were increased with age. Incidence of peliosis at ∼110 weeks of age was higher in female rats. Among the proliferative lesions in rats, higher incidences of cortical cell hyperplasia was observed followed by medullary hyperplasia, complex pheochromocytoma, cortical cell adenoma and cortical adenocarcinoma. In beagle dogs, the incidences of hemangiectasis and cortical cell vacuolation in adrenal glands were higher in 18-21 months aged dogs in both the sexes as compared to 10-12 months of age. In pituitary gland, the incidences of cystic changes were higher in older rats and dogs and the incidences were more in beagles as compared to rats. In thyroid glands, C-cell (parafollicular cells) hyperplasia/complex was observed more frequently in both the species. Few incidences of cystic changes were observed in parathyroid of 18-21 months aged beagle dogs. In endocrine pancreas, few incidences of islet-cell vacuolation, atrophy and hyperplasia were observed in both the species. The Islet cell hyperplasia was found to be more frequent in male rats at ∼110 weeks of age.