Enhancement of erythropoietin production by selective adenosine A2 receptor agonists in response to hypoxia.

Abstract

The purpose of this study was to characterize the effects of two new adenosine A2 agonists, 2-(p-(2-carboxyethyl)phenethyl amino)-5'-N-ethylcarboxamidoadenosine (CGS-21680) and N6-(2(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl)-adenosine (DPMA), on erythropoietin (EPO) production in vivo and in vitro. Intravenous injections of CGS-21680 (100 to 500 nmol/kg mouse/day) and DPMA (50 to 500 nmol/kg mouse/day) for 4 days produced significant increases in serum levels of EPO in exhypoxic polycythemic mice. CGS-21680 (10(-7) to 10(-6) mol/L) and DPMA (10(-8) to 10(-5) mol/L) also produced significant increases in medium levels of EPO in a cloned EPO-producing Hep3B hepatocellular carcinoma cell line after 18 hours of incubation in 1% O2. Both compounds also increased cellular cAMP levels significantly in a dose-dependent manner after 1 hour of incubation. A2 receptor binding assays with tritiated CGS-21680 revealed a single type of adenosine receptor binding site on Hep3B cell membranes with a dissociation constant of 132.9 nmol/L and a binding capacity of 270.6 fmol/mg protein. The Ki competition binding values versus tritiated CGS-21680 were 217 nmol/L for CGS-21680 and 86.8 nmol/L for DPMA. These results indicate that adenosine A2 receptor activation amplifies EPO production in response to hypoxia, both in vivo and in vitro.