Effect of prolactin and bromocriptine on growth of transplanted hormone-dependent mouse mammary tumours.

Administration of ovine prolactin alone supported growth of hormone-dependent GR mouse mammary tumours. Growth of hormone-independent tumours was not stimulated. Furthermore, administration of bromocriptine, a compound that inhibits release of prolactin from the pituitary gland, was shown to inhibit the growth of hormone-dependent tumours in animals receiving treatment with progesterone + oestrone. Administration of prolactin or bromocriptine to mice bearing tumours that grew independently of progesterone + oestrone treatment had no influence on tumour growth. We conclude that direct as well as indirect evidence has been found for the involvement of prolactin in the growth of transplanted, hormone-dependent GR mouse mammary tumours.