Haloperidol and oestrogens induce c-myc and c-fos expression in the anterior pituitary gland of the rat.

Decreased dopaminergic and increased oestrogenic effects induce prolactin release and DNA synthesis in prolactin secreting cells of the adult male rats. Oestrogen treatment for 7 days significantly increased the levels of prolactin, c-myc and c-fos mRNAs. The effect of oestrogens was reversed by the administration of the dopaminergic agonist bromocriptine. There was an early gradual increase of c-myc mRNA levels beginning 30 min after the injection of the steroid. c-fos mRNA levels increased sharply 15 min after oestrogen administration and decreased to basal values 15 min later to remain at this level over the period of time evaluated. Administration of the dopaminergic antagonist haloperidol did not change the levels of protooncogenes mRNA. However, in rats previously treated with oestrogens for 7 days c-myc mRNA levels increased 90 min after the injection of haloperidol and decreased to basal values after 2.5 h. c-fos mRNA levels increased sharply 30 min after haloperidol administration and also decreased to basal values 1 h later. We propose that changes in protooncogenes expression may be involved in the stimulation of cell proliferation induced by prolactin secretion.