title: Fractionated low-dose radiation exposure potentiates proliferation of implanted tumor cells.
abstract: OBJECTIVE
  The purpose of this study is to test whether whole-body fractionated exposure of tumor-free animals to low doses of low-LET radiation (at the total delivered dose of 1.0 Gy of X-rays) is capable of potentiating growth of subsequently implanted tumor cells.
  
  
  METHODS
  Adult male rats were fractionally exposed to low doses of X-rays (10 acute exposures with 0.1 Gy each and with a frequency of 1 exposure per 3 days). The next day after the last irradiation rats were implanted with Guerin carcinoma (GC) cells. On the 12th and 18th days after implantation of GC cells, animals were sacrificed, and the mass of tumors was measured by weighing them, although the kinetics of tumor growth was also examined by daily measurements of the dimensions of tumors. Cytotoxic effects in the bone marrow were assessed flow cytometrically in acridine orange-stained unfractionated bone marrow cells using the ratio of polychromatic erythrocytes (PCE) to normochromatic erythrocytes (NCE).
  
  
  RESULTS
  In irradiated rats, tumors grew apparently faster than in unirradiated rats for up to 18 days after implantation of GC cells. On the 18th day after implantation of GC cells the average value of the mass of tumors in irradiated rats was 2.8-fold higher compared with the average value of the mass of tumors in unirradiated rats (p < 0.05). On this day post-implantation, the bone marrow in irradiated animals was 1.8-fold more suppressed (as evidenced by decreased PCE/NCE ratios) than that in animals that were irradiated, but were not implanted with GC cells (p > 0.05), and was 1.4-fold more suppressed than that in animals that were not irradiated, but were implanted with GC cells (p > 0.05).
  
  
  CONCLUSIONS
  Fractionated irradiation of tumor-free animals with low doses of X-rays potentiates proliferation of subsequently implanted GC cells. This potentiation seems to be associated with radiation-induced impaired hematopoiesis.
authors.affiliation: R.E. Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology, NAS of Ukraine, Kyiv 03022, Ukraine. biger63@yahoo.com
authors.forename: B I
authors.initials: BI
authors.lastname: Gerashchenko
authors.forename: N M
authors.initials: NM
authors.lastname: Ryabchenko
authors.forename: O A
authors.initials: OA
authors.lastname: Glavin
authors.forename: N K
authors.initials: NK
authors.lastname: Rodionova
authors.forename: L I
authors.initials: LI
authors.lastname: Makovetska
authors.forename: O B
authors.initials: OB
authors.lastname: Ganzha
authors.forename: M O
authors.initials: MO
authors.lastname: Druzhyna
authors.forename: V M
authors.initials: VM
authors.lastname: Mikhailenko
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000528:radiation effects*; D001854:Bone Marrow Cells / Q000528:radiation effects; D049109:Cell Proliferation / Q000528:radiation effects*; D019583:Dose Fractionation, Radiation; D004912:Erythrocytes / Q000528:radiation effects; D006410:Hematopoiesis / Q000528:radiation effects; D008297:Male; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000473:pathology*; D011829:Radiation Dosage; D051381:Rats; D014916:Whole-Body Irradiation