Incidence and characteristics of colony-forming units fibroblasts (CFU-F) in the bone marrow of weanling mice treated with cytosine arabinoside and phenylhydrazine: correlation with CFU-S, progenitors of diffusion-chamber colonies (CFU-D), and CFU-C.

A study of murine adherent marrow cells (AMC) under conditions of high and low concentrations of hematopoietic stem cells and progenitors was carried out. In one group of weanling mice, decreased marrow cellularity and increased concentrations of CFU-S, CFU-D, and CFU-C were observed two days after administration of two consecutive intraperitoneal (i.p.) cytosine arabinoside (Ara-C) injections (2 x 200 ng/kg, at 6 h interval). Fibroblast colony-forming units (CFU-F) of this marrow were studied. In a second group of mice, which were given three i.p. phenylhydrazine (PHZ) injections (3 x 60 mg/kg on days 0, 1, and 3), CFU-S and CFU-C levels were unchanged or lowered 6 days after the start of PHZ administration. In these animals, however, the number of CFU-D was four times higher than in controls. The study of CFU-F in experiments of groups 1 and 2 indicated a high concentration of these progenitors in group 1 and lower concentration in group 2. Furthermore, fibroblastoid colonies produced in vitro by CFU-F of Ara-C-treated marrow were significantly larger than colonies from control marrow, and they markedly inhibited G/M colonies in split-phase agar cultures. By contrast, fibroblastoid colonies produced by PHZ-treated marrow were of regular size and did not inhibit G/M colonies from test bone marrow.