Evidence for specific binding and stimulatory effects of recombinant human erythropoietin on isolated adult rat Leydig cells

The presence of specific binding of recombinant human erythropoietin and its effect on testosterone production were evaluated in isolated intact adult rat Leydig cells. Maximal specific binding was observed after 135 min incubation at 34°C. Scatchard analysis of the binding data revealed two distinct classes of binding sites for [125I]-recombinant human erythropoietin with dissociation constants of (Kd1) 1.9 x 10-10 mol/l and (Kd2) 1.37 x 10-8 mol/l respectively and binding capacity of (Bmax1) 12.3 fmol/106 cells and (Bmax2) 42.8 fmol/106 cells, respectively. GnRH, hCG, IGF-1 and EGF did not induce any modification of recombinant human erythropoietin-specific binding. Recombinant human erythropoietin added to isolated adult rat Leydig cells exerted a stimulatory effect on testosterone production reaching its maximal effect at the dose of 10-10 mol/l (testosterone production from 14.9 ± 1.7 to 45.1 ± 6.2 pmol/106 cells/3 h). Addition of anti-recombinant human erythropoietin serum completely blocked the recombinant human erythropoietin-stimulated testosterone production. These results show that purified adult rat Leydig cells possess recombinant human erythropoietin specific binding, and suggest that this glycoprotein directly influences rat Leydig steroidogenesis.