Prolactin-secreting pituitary adenomas with mammary dysplasia in New Zealand white rabbits.

Nine aged (mean age = 3.2 years) nulliparous New Zealand white rabbit does were found to have markedly enlarged teats. The teats were frequently engorged with fluid but were not hot and did not cause signs of pain. The number of affected teats per animal ranged from 1 to 8 (mean = 4). The teats and associated glandular tissue were typically discolored grey, blue, or greenish black (n = 6). Prolactin concentrations were evaluated by radioimmunoassay. Serum prolactin concentrations ranged from 22.4 ng/ml to 2.21 micrograms/ml (mean = 397.3 ng/ml), which was 10- to 1000-fold greater than normal values in nonpregnant rabbits. Conventional radiography of the skull of six rabbits did not reveal pituitary enlargement. Necropsy revealed an enlarged pituitary gland and sella turcica in six of nine does. The diaphragma sellae had ruptured in two rabbits. All nine rabbits had pituitary acidophil adenomas. The neoplastic portions of the pituitaries were diffusely immunoreactive when stained immunohistochemically for prolactin. In contrast, only small clusters of five to seven cells stained positively in normal pituitaries selected as controls. Histologic examination of the mammary glands revealed numerous large dilated cystic spaces containing proteinaceous fluid. Many cysts had numerous papillary epithelial infoldings. The cystic dilations extended into and included the teat canal producing the gross appearance. Prolactin-secreting acidophil adenomas have not been previously reported in the rabbit, and the association with mammary dysplasia is unique.