Abstract
Summary
Vinblastine given in graded doses, 10-20-40 μg, to polycythemic mice either before or after EP reduces their response to EP in proportion to log dose. Analysis of the dose response curve using Valeriote and Bruce model(5) suggests a generation time of about 9 hours for the erythropoietin responsive unit (ERU). Methotrexate 50 mg/kg given either 8 hours before, together with, or 4 hours after EP completely suppresses the response to EP even though, followed after a 4-hour interval by an injection of Folinic acid which is known to reverse the methotrexate effect on cells. It is suggested that most of ERU are in cell cycle, and respond to EP in G1. The ERU population might be that segment of CFU in cycle, or an intermediary population, capable of limited divisions, derived from it.
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