Studies of the Influence of Cyclic Nucleotides on in Vitro Haemoglobin Synthesis

Abstract

Over a wide range of concentrations, dibutyryl cyclic AMP (db-cAMP) was either ineffective or inhibited Hb synthesis by marrow cells from rat, mouse and guinea-pig. 10-3 M db-cAMP consistently stimulated Hb synthesis in cultures of human, sheep, rabbit and canine cells, with the latter being most responsive. This effect, which approached in magnitude that of erythropoietin (ESF) itself, was specific for cAMP and its mono- and dibutyryl derivatives and was not inhibited by anti-ESF. Adenosine, AMP, ADP, ATP, cGMP, db-cGMP, cCMP, cIMP and sodium butyrate were either inactive or inhibitory at similar concentrations. Enhancement of Hb synthesis was also observed with the phosphodiesterase inhibitor, RO-20-1724. The susceptibility to ionizing radiation of the response to ESF and db-cAMP was marked, indicating that the increased Hb synthesis in this system was proliferation dependent, although the response to db-cAMP was less radiosensitive. Studies with tritiated thymidine showed that about 50% of the cells which were responding to either db-cAMP or ESF were actively engaged in DNA synthesis. The physical characteristics of db-cAMP- and ESF-responsive cells were dissimilar as analyzed by their velocity sedimentation properties. cAMP apparently has a major stimulatory effect on Hb synthesis with cells from selected mammalian species with activity approaching that of ESF, but the target cells most responsive to these agents appear different. The results suggest that cyclic nucleotide-related mechanisms may modulate in vitro erythropoiesis.