Specific binding of luteinizing hormone to leydig tumor cells

Abstract

A radioimmunoassay was used to detect luteinizing hormone (LH) bound to washed Leydig tumor cells. Tumor cell suspensions were incubated with LH at 37° and washed repeatedly by centrifugation with isotonic 0.9% NaCl solution. The tumor cells contained large quantities of LH even after they were washed sufficiently to produce a 10⁶-fold dilution of unbound LH. Six washings (10⁶-fold dilution) were no more effective in removing LH from the cells than three washings (10³-fold dilution). Binding was not influenced by the temperature at which the cells were washed. The extent of LH binding was related to the number of cells, with approximately 5300 ± 960 molecules of LH bound per cell. LH binding was also proportional to the same concentrations of LH which produced a steroidogenic dose response curve. The binding constant of 1.5 × 10^-8 m was considered to be higher than that expected for nontumorous tissues. Tumor cells bound more LH than did erythrocytes or thymocytes under the same conditions.