Detection of prolactin based on the receptor-binding activity and its application

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Prolactin sends its hormonal message to target organs through binding with its receptor located on the plasma membrane. Shill et al. reported that the receptor-binding activity of prolactin correlates well with its biological activity. -However, various molecular forms of prolactin have been identified. Among them, for example glycosylatede prolactin is less active than nonglycosylated prolactin. The microsome fraction has been used as a source of the receptor. In the present experiments, we solubilized these membrane proteins with Triton X-100, purified partially using Con-A affinity chromatography, and then immobilized them on a nitrocellulose membrane filter. Using membrane-bound receptor and bovine serum, the serum level of prolactin was determined by radioreceptor assay. The dosedisplacement curve was obtained in the range of 0.4 and 20 ng/ml. Serum could be included in concentrations up to 16% of the assay buffer and, thus the detection limit was about 2.5 ng/ml. Prolactin in the serum was determined by mdioimmunoassay. The ratio of the two assays was nearly 0.99 (r>+O. 99, n=55). The gel filtration profile was identical between the two assays. It was concluded that membranebound receptor can be used for the determination of serum prolactin with satisfactory.