The properties and purification of a prolactin receptor and the development of a radioreceptor assay for lactogenic hormones.

A cell membrane component(receptor) which binds prolactin and other lactogenic hormones with a high degree of specificity and affinity has been identified and studied in mammary glands obtained from pregnant and lactating rabbits. In rat mammary tumors induced by 7,12-dlmethylbenzanthracene a significant positive correlation was found between the binding of prolactin to membrane fractions isolated from the tumors and the growth response of the tumors to the administration of prolactin, suggesting that the prolactin receptor is one factor which determines the degree of hormonal dependency of these tumors. The particulate membrane receptor isolated from the rabbit mammary gland has been solubilized with the non-ionic detergent, Triton X-100. The solubilized receptor(molecular weight 220,000) has been purified approximately 1500-fold by affinity chromatography. Using the membrane receptor preparation for the measurement of prolactin, a sensitive and reproducible radioreceptor assay has been developed. The levels of prolactin determined by this technique in a variety of samples correlate well with those obtained by standard radioimmunoassay and bioassay procedures. The assay has been utilized to identify and measure several new placental lactogenic hormones which are secreted during pregnancy in a number of species, e.g., rat, mouse, hamster, guinea pig and sheep