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The Generation Time of Marrow Nucleated Erythroid Cells in 6-Day-Old and Adult Rats 1

Summary The generation time of marrow nucleated erythroid cells was estimated with a colchicine technic in adult and 6-day-old Sprague-Dawley rats. Extrapolation of metaphase accumulation to 100% provided comparable estimates for these age groups. Cell cycle parameters were: generation time (tG )≈ 10.5 hr: mitotic interval (tM ) 40 min adult vs 60 min 6 day old; metaphase interval (t Metaphase) 31 min adult vs 53 min 6 day old. The higher erythroid mitotic index (MI) in the neonatal animal appears best explained by a longer duration of mitosis. Neonatal animals were more sensitive to the stathmokinetic effects of colchicine. The change in sensitivity to colchicine appeared to parallel the transition of neonatal to adult erythropoiesis.