Endocrine Abstracts

Background: Pituitary tumours are commonly benign adenomas, accounting for 10-15% of all intracranial neoplasms. Among functioning pituitary tumours, prolactinomas are the most frequently observed in the clinic (about 40%). Dopamine, acting through the dopamine type 2 receptor (Drd2), is the main inhibitor of lactotroph proliferation and prolactin secretion, therefore, these tumours are usually treated with dopaminergic agonists with a high efficiency. However, there is a subset of prolactinomas (15 and 20%) that do not respond to this treatment, named dopamine agonist resistant prolactinomas, which represent a major challenge for clinical management, because up to date, no alternative treatments have been found. Transforming growth factor β1 (TGFβ1) and activins are known inhibitors of lactotroph cell proliferation and prolactin secretion.

Aims: Study the role of TGFβ1 and activins in normal and tumoral pituitaries, in 3 animal models of prolactinomas.

Hypothesis: We postulate that, due to the inhibitory action on lactotroph functions exercised by the intra-pituitary members of the TGFβ-family, these factors represent novel targets to develop alternative treatments for resistant prolactinomas.

Results: We demonstrated, in 3 different animal models of prolactinomas, the Drd2 knock-out mice, the estrogen-treated rat and the hCGβ overexpressing mice, that:

1. Pituitary TGFβ1 activity, several components of the TGFβ1 system (LTBPs, TβRII, local activators), as well as activin and activin-receptors expression are reduced in prolactinomas vs normal pituitaries;

2. in vivo pharmacological treatments that recover pituitary TGFβ1 activity reduce the hyperprolactinemia and counteract the tumour growth;

3. TGFβ1 activity and activin expression are higher in male pituitaries (sex differences: protective factors?),

4. Ovariectomy in animal models of prolactinoma recovers pituitary TGFβ1 activity and activin expression preventing prolactinoma development.

Conclusion: These findings open new possible therapies in treatment for prolactinomas, especially in those that are resistant to dopaminergic drugs.