Pituitary adenoma with prolactin and growth hormone production in a sheep

A pituitary adenoma was found in a 6-year-old ewe. This tumour was composed mainly of chromophobic cells, but acidophilic cells predominated in a few areas. Prolactin was demonstrated in the cytoplasm of some chromophobic cells by means of the immunoperoxidase technique, and secretory granules ranging in size from 100 to 900 nm in diameter were seen in all chromophobic cells examined. Almost all acidophilic cells were positive for growth hormone (GH), and a few of them were also positive for prolactin (PRL). This tumour resembled a human mixed GH cell-PRL cell adenoma.