Estrone-induced, prolactin-secreting and dopamine-sensitive rat pituitary tumor

Prolactin (PRL)-secreting rat pituitary tumors were induced in female Fisher 344/Lis rats by s.c. implants of estrone (E1) pellets. Tumor growth was relatively fast and reached about 100 mg within 2 months. Ovariectomy at the time of E1 implants seemed to accelerate the growth of the tumors. Tumor cells in primary culture produced mainly PRL, while growth hormone (GH) release was about 2% of PRL production and the release of some other pituitary hormones did not exceed 1% of PRL values. Tumor cells were found to have high-affinity dopamine (DA) receptors. The addition of DA in vitro at 10(-10) M concentration stimulated PRL release, while at 10(-6) M concentration it inhibited the release of the hormone by more than 50% of control values. Histological, immunohistochemical and electron microscopical studies demonstrated the tumor to be composed mainly of maximally stimulated mammotrophs.