Abstract
Summary
The present study has demonstrated that terbutaline sulfate, a specific β-2 adrenergic agonist drug produces a direct in vitro action causing an increase in the number of CFU-E in the rabbit bone marrow cell compartment. Terbutaline in combination with Ep did not cause any greater increase in 59Fe incorporation into extracta-ble heme in vitro after 45-hr incubation than Ep alone. However, Ep and terbutaline in concentrations between 10-10 and 10-6 M produced highly significant increases in the number of rabbit bone marrow erythroid colonies in an in vitro plasma clot system following 96-hr incubation compared with Ep alone. Erythroid colony growth in the plasma clot system was found to require Ep. It is postulated that the stimulatory effects of terbutaline on CFU-E are via β-adrener-gic receptors, in that erythroid colony formation was blocked by the β-adrenergic antagonist, DL-propranolol. The observation that terbutaline did not produce an increase in heme synthesis may indicate that this β-2 adrenergic agonist is acting on an early stem cell population which is responsive to Ep, in that terbutaline alone was without an effect on the CFU-E cell compartment.
The authors would like to thank the Ayerst Laboratories for the generous supply of DL-propranolol and CIBA-GEIGY for the terbutaline sulfate.
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