Binding of ovine 125I-prolactin to cultured anterior pituitary tumour cells and normal cells

Abstract

THE first report of specific, high affinity and low capacity binding of radioiodinated ovine prolactin to homogenate particles from lactating mouse mammary glands, liver and several other organs of rats and mice1 was followed by a radioreceptor assay for prolactin using purified mammary fractions2. Other reports of prolactin binding have been with reference to a variety of crude or partially purified membrane fractions3–7 or tissue slices8–10. These can be assumed to describe various degrees of submaximal binding response because of proteolysis, denaturation or structural factors that restrict free access of the hormone to capable binding sites. We now report specific, high affinity, low capacity binding of radioiodinated prolactin to cultured rat anterior pituitary cells, from two sources—those derived from oestradiol-induced anterior pituitary tumours, and normal anterior pituitary glands. Both cells lines were shown by radioimmunoassay to secrete prolactin. In addition to the possible significance of these findings with respect to pituitary control mechanisms they indicate the recommendation of the development of radioreceptor assays based on cultured cell lines as a source for specific binding sites. The technology seems to be available to develop a standardised assay of great convenience and versatility, which models better the conditions for hormone action in vivo; the regulatory hormone ‘sees’ only the outside of an intact cell in a favourable environment for specific interaction.