Abstract
Chromophobe adenomas from 8 dogs with clinical signs and lesions of hyperadrenocorticism (Cushing's-like disease) were selected for electron microscopic study in order to establish a morphologic basis for active secretion by the neoplastic cells. At the level of ultrastructure there was definite evidence of secretory activity and the organelles concerned with protein synthesis (endoplasmic reticulum) and packaging of secretory products (Golgi apparatus) were well developed. Although the numerous secretory granules present varied in electron density and in size, the most frequently encountered granule measured 170 mμ in diameter. The secretory granules of the neoplastic cells differed from those found within acidophils and basophils of the canine hypophysis. Based on these findings it was concluded that the cells comprising these chromophobe adenomas were actively secreting corticotrophs of the pituitary gland.