and hyperprolactinemia. In these rats the administration of the dopaminergic agonist bromocriptine reduces the levels of serum prolactin and the size of the pituitary gland [5, 6]. Estrogens also stimulate cell proliferation in breast tissue and the presence of estrogen receptors in breast cancer is an important sign in the degree of differentiation and an important indication of prognosis and treatment selection [7, 8]. Thus, the presence of estrogen receptors in breast cancer indicates a more differentiated tissue and a better prognosis than the absence of this protein. Furthermore the concentration of estrogen receptors in breast cancer cells contributes to the stadifi cation of breast cancer and allows making a rational decision on the usefulness of the treatment with anti-estrogen [9]. Although pituitary tumors are almost entirely histologically benign, their behavior varies considerably after surgery and / or in their response to dopaminergic agonists. Some of them are fast growing adenomas and relapse rapidly after surgery requiring treatment with dopaminergic agonists almost immediately. Others are apparently cured by surgery: prolactinemia remains within normal range and there are no signs of regrowth. There are all kinds of intermediate cases between these two above mentioned options. We have shown that dopaminergic ago-Authors

The presence of thyroid hormone receptors in pituitary tumors is in line with two important characteristics of these tumors: they are histologically benign and well differentiated.