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Oophorectomy improves pituitary activin inhibitory function preventing lactotroph hyperplasia.

Among pituitary adenomas, prolactinomas are the most frequently diagnosed (about 50%). Dopamine agonists are generally effective in the treatment of prolactinomas. However, a subset of about 25% of patients does not respond to these agents. The management of drug-resistant prolactinomas remains a challenge for endocrinologists and new inhibitory treatments are needed. Pituitary activins inhibit lactotroph function. Its expression and action were found reduced in animal models of lactotroph hyperplasia (female mice overexpressing the β subunit of the human chorionic gonadotrophin and female mice knockout for dopamine receptor type 2). In these models, an oophorectomy avoids prolactinoma development. Hormonal replacement with estradiol and/or progesterone is not enough to reach the tumour size observed in transgenic females. We postulated that the loss of gonadal inhibins after an oophorectomy contributes to prevent hyperplasia development. Here we demonstrated that an oophorectomy at 2 month-age recovers, in adulthood: 1. Pituitary activin expression, 2. Activin receptor expression specifically in lactotroph population, 3. activin biological activity in lactotrophs with a concomitant reduction of Pit-1 expression. Summarizing, when an oophorectomy is performed, inhibins are lost and the inhibitory action of pituitary activins on lactotroph population is recovered, helping to prevent lactotroph hyperplasia development. These results emphasize the importance of the inhibitory action of activins on lactotroph function, positioning activins as a good therapeutic target for the treatment of resistant prolactinomas.