Lack of effect of erythropoietin on cyclic adenosine-3',5'-monophosphate levels in rat fetal liver cells.

Abstract

Abstract The effect of Erythropoietin (Ep) and epinephrine on the cellular concentration of adenosine 3′,5′-cyclic monophosphate (cAMP) was studied using suspensions of fetal liver cells obtained from 14-day pregnant rats. This system was chosen because the cell suspensions were greater than 65 per cent erythroid and very sensitive to Ep. In cells preincubated with theophylline, Ep failed to increase cAMP levels after both 5 minute and 30 minute incubations with the hormone. By contrast, epinephrine stimulated cAMP concentrations 6- to 7-fold indicating that the adenyl cyclase present was capable of responding to an appropriate stimulus. In suspensions first treated with epinephrine to raise cAMP levels, addition of Ep did not lower the concentration of this nucleotide. Heme synthesis experiments employing the same conditions as the cAMP studies show that Ep effectively stimulated 59 Fe incorporation into heme. This indicated that under the conditions of the cAMP studies the hormone was fully capable of interacting with the erythropoietin-responsive cell. The above experiments show that erythropoietin can stimulate hemoglobin synthesis in vitro without producing any detectable increase or decrease in the cellular cAMP concentration. Thus, the data fail to support the hypothesis that the effect of Ep on red-cell production is mediated by a change in cAMP levels.