ACTH-producing pituitary tumors in transgenic mice. An ultrastructural and immunoelectron microscopic study

Ultrastructural and electron microscopic immunohistochemical features of corticotropic pituitary tumors arising in polyoma large T transgenic mice and the corresponding tumor transplants in non-transgenic mice are reported. Spherical, irregular and drop-shaped secretory granules measuring 150-450 nm in diameter, were seen in all tumors. Both in tumors from transgenic mice and in tumor transplants immunoreactivity for adrenocorticotropic hormone (ACTH) and beta-endorphin was expressed in the majority of the secretory granules, whereas growth hormone (GH) immunoreactivity was demonstrated only in a small number of cells in tumors from transgenic mice. In addition, positive immunostaining for neuron-specific enolase (NSE) and synaptophysin was found in the two pituitary tumor transplants tested. The study shows that the pituitary tumors from transgenic mice and their tumor transplants have features similar to human corticotropic pituitary tumors, and may therefore be a valuable model for experimental studies of the tumorigenesis.