RADIOIMMUNOASSAY OF RAT PROLACTIN . PROLACTIN LEVELS IN PLASMA OF RATS WITH SPONTANEOUS PITUITARY TUMOURS, PRIMARY OESTRONE-INDUCED PITUITARY TUMOURS OR PITUITARY TUMOUR TRANSPLANTS

In old female rats a close correlation was observed between detecting elevated prolactin levels in the circulation and the presence of spontaneous pituitary tumours on the one hand and mammary tumours on the other hand. Weekly oestrone-cholesterol pellet implantation in a group of 4 orchidectomized rats resulted in a rapid rise in prolactin plasma levels, indicative of very high secretion rates of this hormone by the pituitary gland as a consequence of oestrone stimulation. These high rates of secretion apparently were maintained for over 110 days without great fluctuations. Between day 110 and day 150 a further and more or less progressive increase of plasma prolactin was found to occur, which probably was related to the progressive increase in weight of the pituitary occurring around this time in this strain of rats under this regimen. Rats bearing transplants of oestrone-induced pituitary tumours and in which one oestrone-cholesterol pellet was implanted monthly showed great variations in prolactin output in response to the oestrone stimulus as well as great variations in the rate of growth of the grafts. The majority of the grafts, however, responded with a maximum outflow of prolactin reflected in high plasma values around 2 weeks after implantation of the oestrone. The findings suggested that an extreme hyperfunction that will maintain high prolactin levels over long periods of time was not primarily caused by implantation away from the restraining influence of the hypothalamus, but was consequent to relatively high doses of oestrogen. © 1969.