Effect of bromocriptine on DNA synthesis, growth and hormone secretion of spontaneous pituitary tumours in the rat.

The 'spontaneous' development of pituitary tumours has been studied in the Wistar-Furth strain of rat. In females aged 64--135 weeks the incidence was as high as 69% whereas in males aged 72--116 weeks only 6% developed tumours. Hyperprolactinaemia was invariably associated with these spontaneous pituitary tumours but excessive secretion of growth hormone (GH) was found in one animal only. Bromocriptine inhibited secretion of prolactin and DNA synthesis of the tumours. In a mixed GH- and prolactin-secreting tumour transplanted to a peripheral site, bromocriptine reduced the size of the tumour as well as the secretion of both hormones. Oestradiol reversed the inhibitory action of bromocriptine on prolactin secretion and tumour growth but failed to influence the reduction in GH secretion caused by the drug.