Endocrine Abstracts

Pituitary tumours occur in more than 40% of multiple endocrine neoplasia type 1 (MEN1) patients, and these are more aggressive and difficult to treat than those in non-MEN1 patients. Assessments of in vivo proliferation rates will be of importance in evaluating emerging treatments. We have used the uptake of the DNA nucleotide precursor, 5-bromo-2-deoxyuridine (BrdU), to assess proliferation rates of pituitary tumours in our Men1 knockout mouse model, which develops pancreatic islet, parathyroid and anterior pituitary tumours that are predominantly prolactinomas. BrdU is recognised to be the most reliable marker of cell proliferation as it allows the substitution of an endogenous DNA base, thymidine, with the BrdU analogue, ensuring specific labelling during S-phase of only the dividing cells. Mice were kept in accordance with UK Home Office welfare guidelines and project licence restrictions. Drinking water containing BrdU at 1 mg/ml was given to 19–21 month old wild-type (+/+) and Men1 heterozygous (+/−) littermates for 4 weeks. Pituitary sections were immunofluorescently labelled with DAPI, prolactin and BrdU, and six sections from wild-type pituitaries or pituitary tumours from four animals per genotype were analyzed to determine the percent of BrdU-positive cells. The mean (±S.E.M.) proliferation rate of anterior pituitary tumours, which was immunostained with prolactin, from Men1^+/− mice (1.32±0.210%) was significantly higher than pituitaries from wild-type Men1^+/+ littermates (0.02±0.003%, P<0.001). Indeed, the proliferation rate of lactotrophs in the tumours from Men1^+/− mice was over 60 times greater than that in the normal pituitaries of wild-type mice. These results demonstrate that the tumours of the anterior pituitary, which are prolactinomas in the Men1^+/− mice, have a higher proliferation rate and this opens up the way to assess the effectiveness of new anti-proliferative therapies for pituitary tumours.