CHARACTERIZATION OF THE PRIMATE LUTEINIZING-HORMONE RECEPTOR IN TESTIS HOMOGENATES AND LEYDIG-CELLS

The interaction of [125I]hCG with the primate LH receptor was investigated in particulate fractions and cell suspensions from human and rhesus testicular tissue. Binding to testis homogenates was saturable, dose and time dependent, and displaced by low concentrations of unlabeled human LH and hCG. Both the human and rhesus LH receptors were of high affinity (Kn = 2-3 X 1010 M‑1) and low capacity (23-146 fmol/g), and both failed to cross-react with heterologous LH at concentrations up to 1 jug/ml. In contrast, the rat testis LH receptor interacted with several heterologous LH preparations in nanogram concentrations. The species specificity of the primate LH receptor was also demonstrated by recombination studies with isolated subunits of porcine LH and hCG. The presence of the β-subunit of hCG, irrespective of the recombined a-subunit, conferred the ability to inhibit binding of [125I]hCG by the primate testis homogenates. The porcine β-subunit, when recombined with the a-subunit of hCG, failed to inhibit binding of [125I]hCG to primate testicular receptors, whereas the recombined preparation was active in binding to rat testis. Collagenasedispersed human and rhesus interstitial cells responded with increased testosterone production when stimulated by homologous gonadotropins in vitro. Such primate interstitial cells were sensitive to low concentrations of LH and hCG and exhibited the same species specificity as the receptor-binding studies performed with testis homogenate. These studies have shown that LH receptors in the primate testis possess marked species specificity for gonadotropins with interstitial cell-stimulating activity. The species specificity of the primate LH receptor was shown to depend upon recognition of a conformation endowed by the β-subunit of the human glycoprotein hormone. Enzyme-dispersed interstitial cell preparations retained biological responses to human gonadotropins and provided a simple and sensitive in vitro primate bioassay for gonadotropic peptides. The similar properties of human and rhesus testis homogenates and interstitial cell fractions indicate that rhesus testes provide a useful model for research into human gonadotropin receptors and their regulation. © 1979 by The Endocrine Society.