Induction effects of sulfur dioxide inhalation on chromosomal aberrations in mouse bone marrow cells

To investigate the induction of chromosome aberrations (CA) in mouse bone marrow cells by sulfur dioxide (SO(2)) inhalation, mice were treated by SO(2) exposure for 4 h/day for 7 days at various concentrations of SO(2), then mitotic indices and CA in mouse bone marrow cells were analyzed. The present results show that SO(2) might increase the frequencies of CA and aberrant cells in mouse bone marrow in a dose-dependent manner. The frequencies (%) of aberrant cells in mouse bone marrow induced by SO(2) at concentrations of 0, 7, 14, 28 and 56 mg/m(3) were 1.81, 3.00, 3.58, 4.26, 4.86, respectively. At low concentrations SO(2) induced only chromatid-type CA, while at high concentrations SO(2) induced both chromatid-type and chromosome-type CA. SO(2) inhalation decreased the mitotic indices of bone marrow cells. The results imply that SO(2) inhalation may inhibit mitoses and increase CA frequencies of bone marrow cells and that it is a clastogenetic and genotoxic agent. Long exposure to SO(2) pollution at low concentrations in the environment may be a potential risk for induction of cytogenetic damage in vivo in humans.     

Cytogenetic analyses of mice exposed to dichloromethane

Chromosome damage was studied in female B6C3F1 mice exposed to dichloromethane (DCM) by subcutaneous or inhalation treatments. No increase in the frequency of either sister chromatid exchanges (SCEs) or chromosome aberrations (CAs) in bone marrow cells was observed after a single subcutaneous injection of 2,500 or 5,000 mg/kg DCM. Inhalation exposure to DCM for 10 days at concentrations of 4,000 or 8,000 ppm resulted in significant increases in frequencies of SCEs in lung cells and peripheral blood lymphocytes, CAs in lung and bone marrow cells, and micronuclei (MN) in peripheral blood erythrocytes. Lung cell CAs and blood erythrocyte MN reached frequencies of approximately two times control levels. Following a 3-month inhalation exposure to 2,000 ppm DCM, mice showed small but significant increases in lung cell SCEs and peripheral blood erythrocyte MN. These findings suggest that genotoxicity may play a role in the carcinogenicity of DCM in the lungs of B6C3F1 female mice.     

Teratological and cytogenetical evaluation of two antihistamines (pipethiadene and pizotifen maleate) in mice

The teratogenic and cytogenetic effects of two drugs with antihistaminic properties, Pipethiadene and Pizotifen maleate, were investigated. Three groups of pregnant mice were treated daily with oral doses (0.24, 0.6 and 1.2 mg/kg) of these drugs from day 4 to day 16 of gestation. The following parameters were investigated: reproductive health of the dams, external, skeletal and visceral malformations of fetuses and frequencies of micronuclei and chromosome aberrations in bone marrow cells of dams. Oral administration of Pipethiadene or Pizotifen maleate produced no teratogenic effects. No elevation was observed in the frequencies of micronuclei and chromosome aberrations. However, the significant reduction of fetal weight after all doses of Pipethiadene or Pizotifen maleate was found to correlate well with the decreased values of the mitotic indices of bone marrow cells of mice, suggesting a potential embryotoxic effect of the tested substances.     

Cyclophosphamide-induced cytogenetic effects in mouse bone marrow and spleen cells in in vivo and in vivo/in vitro assays

Sister chromatid exchange (SCE) and chromosomal aberration studies have been used to monitor human populations for genotoxic exposure to chemical substances. These monitoring techniques involve collection of blood and/or bone marrow from the exposed subjects and culturing cells for one or two cell cycles with various treatments in culture. The results obtained from such in vivo/in vitro studies may lead to an over- or underestimation of the damage that could occur in vivo. In the present study, which uses a mouse model, the in vivo/in vitro cytogenetic assays (SCEs and chromosomal aberrations) have been compared with similar in vivo systems in bone marrow and spleen cells treated with various doses of cyclophosphamide (CPA). The results indicate a significant difference in CPA-induced cytogenetic endpoints between in vivo and in vivo/in vitro conditions in both organs. However, linear relationships were found between CPA dose and cytogenetic end point analyzed under both conditions. Based on these results it appears that the in vivo/in vitro assay is a useful technique for indicating potential in vivo damage of chemicals.     

Methyl isocyanate: an evaluation of in vivo cytogenetic activity

The ability of inhaled methyl isocyanate (MIC) to induce genotoxic and cytotoxic damage in vivo was evaluated by assessing the induction of chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs) in bone marrow metaphase cells, the induction of micronuclei in polychromatic erythrocytes (MN-PCEs), and the inhibition of bone marrow cellular proliferation and erythropoiesis. B6C3F1 mice were exposed to MIC by two exposure regiments: in two experiments, male mice only were exposed to 3, 10, and 30 ppm for 2 hr; in four experiments, male and female mice were exposed to 1 and 3 ppm (in one experiment, to 6 ppm, also), 6 hr per day for 4 consecutive days. The various cytogenetic endpoints were analyzed in bone marrow and peripheral blood (4-day exposure regimen only) samples taken from bromodeoxyuridine tablet-implanted animals killed 11 to 22 hr after cessation of the exposure to MIC. Exposure to MIC for 2 hr induced a significant delay in cellular proliferation but did not induce a significant increase in CAs, SCEs (evaluated at 3 and 10 ppm, only) or in bone marrow MN-PCEs. Also, this exposure regimen did not inhibit the rate of erythropoiesis. Following exposure to MIC for 4 days, a weak but significant increase in CAs and SCEs was observed in male (in one experiment) and in female (in two experiments) mice. The induction was especially apparent in the single experiment in which mice were exposed to 6 ppm MIC. At this concentration, a significant increase in MN-PCEs in peripheral blood was observed in male but not female mice. Delay in bone marrow cell proliferation was observed in male mice beginning at 3 ppm and in female mice at 6 ppm. The 4-day exposure regimen resulted also in a depressed rate of erythropoiesis, with male mice appearing to exhibit greater depression than female mice. The results demonstrate that exposure to MIC by inhalation results in bone marrow damage, indicating the systemic genotoxic/cytotoxic activity of MIC and/or reactive metabolites.     

A comparison of baseline and cyclophosphamide-induced sister chromatid exchanges in bone marrow and spleen cells of mouse and Chinese hamster

Baseline sister chromatid exchange (SCE) frequencies were investigated in bone marrow and spleen cells of mice and Chinese hamsters. No significant difference in SCE frequency was noted for bone marrow in both species and for bone marrow and spleen in mice on per cell and per pg DNA basis. However, a significant difference was noted between species in spleen and between cell types in Chinese hamsters. Also, statistically significant differences were noted between species for both cell types when the same data were expressed on per chromosome basis. SCE levels in cultured bone marrow and spleen cells after intraperitoneal administration of the antineoplastic drug cyclophosphamide (10 and 20 mg/kg) differed significantly in mice and Chinese hamsters on per cell, per pg DNA content, and per chromosome basis. The spleen cells were much more sensitive to the effects of cyclophosphamide than bone marrow cells in both species. The replicative indices did not differ significantly between treated and control animals in either bone marrow or spleen cells of both species. Since SCE frequency is a sensitive measure of DNA damage, and bone marrow and lymphocytes are the most widely used cell types in human and animal in vivo assays, the methodologies and results reported here may be useful for comparative mammalian cytogenetic studies.     

Antimutagenic activity of afobazole in various regimens of treatment

The influence of a new 2-mercaptobenzimidazole derivative afobazole on cytogenetic effects of dioxidine and cyclophosphamide was studied by counting chromosome aberrations in bone marrow cells of C57Bl/6 mice. Afobazole (1-100 mg/kg perorally) exhibited antimutagenic activity determined by its antioxidant properties. This activity depended on the dose and treatment shedule.     

Salubrious effects of dexrazoxane against teniposide-induced DNA damage and programmed cell death in murine marrow cells

The intention of the present study was to answer the question whether the catalytic topoisomerase-II inhibitor, dexrazoxane, can be used as a modulator of teniposide-induced DNA damage and programmed cell death (apoptosis) in the bone marrow cells in vivo. The alkaline single cell gel electrophoresis, scoring of chromosomal aberrations, micronuclei and mitotic activity were undertaken in the current study as markers of DNA damage. Apoptosis was analysed by the occurrence of a hypodiploid DNA peak and caspase-3 activity. Oxidative stress marker such as intracellular reactive oxygen species production, lipid peroxidation, reduced and oxidised glutathione were assessed in bone marrow as a possible mechanism underlying this amelioration. Dexrazoxane was neither genotoxic nor apoptogenic in mice at the tested dose. Moreover, for the first time, it has been shown that dexrazoxane affords significant protection against teniposide-induced DNA damage and apoptosis in the bone marrow cells in vivo and effectively suppresses the apoptotic signalling triggered by teniposide. Teniposide induced marked biochemical alterations characteristic of oxidative stress including accumulation of intracellular reactive oxygen species, enhanced lipid peroxidation, accumulation of oxidised glutathione and reduction in the reduced glutathione level. Prior administration of dexrazoxane ahead of teniposide challenge ameliorated these biochemical alterations. It is thus concluded that pretreatment with dexrazoxane attenuates teniposide-induced oxidative stress and subsequent DNA damage and apoptosis in bone marrow cells. Based on our data presented, strategies can be developed to decrease the teniposide-induced DNA damage in normal cells using dexrazoxane. Therefore, dexrazoxane can be a good candidate to decrease the deleterious effects of teniposide in the bone marrow cells of cancer patients treated with teniposide.     

Comparative cytogenetic analysis of bone marrow damage induced in male B6C3F1 mice by multiple exposures to gaseous 1,3-butadiene

Groups of male B6C3F1 mice (N = 12) were exposed to ambient air or to gaseous 1,3-butadiene (BD) at 6.25, 62.5, and 625 ppm for 10 exposure days (6 hr + T90/day). Exposure to BD induced in bone marrow: 1) a significant increase in the frequency of chromosomal aberrations (CA); 2) a significant elevation in the frequency of sister chromatid exchanges (SCE); 3) a significant lengthening of the average generation time (AGT); 4) a significant depression in the mitotic index (MI); and, as measured in the peripheral blood, 5) a significant increase in the proportion of circulating polychromatic erythrocytes (%PCE), and 6) a significant increase in the level of micronucleated PCE (MN-PCE) and micronucleated normochromatic erythrocytes (MN-NCE). The most sensitive indicator of genotoxic damage was the frequency of SCE (significant at 6.25 ppm), followed by MN-PCE levels (significant at 62.5 ppm), and then by CA and MN-NCE frequencies (significant at 625 ppm). The most sensitive measure of cytotoxic damage was AGT (significant at 62.5 ppm), followed by %PCE (significant at 625 ppm), and then by MI (significant by trend test only). Because each cytogenetic endpoint was evaluated in every animal, a correlation analysis was conducted to evaluate the degree of concordance among the various indicators of genotoxic and cytotoxic damage. The extent of concordance ranged from a very good correlation between the induction of MN-PCE and the induction of SCE (correlation coefficient r = 0.9562) to the lack of a significant correlation between the depression in the MI and any other endpoint (r less than 0.37).     

Use of chromosome painting for detecting stable chromosome aberrations induced by melphalan in mice

Chromosomal aberrations are a measure of genomic instability, which is known to play a key role in the initiation and promotion of carcinogenesis. Stable reciprocal translocations are of particular importance since they are often involved in neoplastic transformation and tumor cell clonal evolution. In this study, chromosome painting analysis was used to test for stable aberrations induced in the bone marrow of C57BL/6J and FVB mice exposed for 4 weeks to 2 or 4 mg/kg of melphalan (MLP), a chemotherapeutic agent with carcinogenic potential. To compare the chemical-induced damage in different tissues, chromosome aberrations were also analyzed by chromosome painting in the spleen of C57BL/6J mice. At the 2 mg/kg dose, MLP induced comparable levels of chromosome-type aberrations in bone marrow cells of both mouse strains and in splenocytes of C57BL/6J mice. At 4 mg/kg, no further increase in aberrations was detected in bone marrow, while a dose-effect relationship was found in spleen cells. This different response may result from a negative selection against highly damaged bone marrow cells during mitotic proliferation. The results indicate that chromosome painting is a useful tool for detecting stable chromosome aberrations in somatic cells exposed to MLP and possibly to other genotoxic chemical carcinogens.     

Cytogenetic studies of sodium fluoride in mice

The cytogenetic effects of sodium fluoride (NaF) were measuredin mice following administration in the drinking water for 6weeks. Bone fluoride levels were determined and showed a dose-relatedincorporation of fluoride. Micronuclei were measured in peripheralblood erythrocytes following 1 and 6 weeks of NaF administration.Bone marrow cell preparations were examined for the presenceof chromosome aberrations following 6 weeks of treatment; metaphaseand anaphase cells were examined. Anaphase cells were scoredin three independent laboratories, two of which also scoredmetaphase cells from the same slides. No increases in micronucleiwere seen in peripheral erythrocytes at either time point, andno increases in chromosome aberrations were seen in bone marrowcells when metaphase or anaphase cells were examined. A concurrentpositive control, cyclophosphamide, produced significant increasesin peripheral blood cell micronuclei and in chromosome aberrationsin bone marrow cells in metaphase. No increases in aberrationswere seen in the same cyclophosphamide-treated mice when anaphasecells were examined. ⁶To whom correspondence should be addressed     

Chromosome aberrations and telomere length modulation in bone marrow and spleen cells of melphalan-treated p53+/- mice

The p53 gene regulates cell cycle and apoptotic pathways after induction of DNA damage. Telomeres, capping chromosome ends, are involved in maintaining chromosome stability; alterations of their length have been related to increased levels of chromosomal aberrations. To study a possible interaction between chromosome aberrations, telomere dysfunction, and p53, we investigated via painting analysis the induction and persistence of chromosome aberrations in bone marrow and spleen cells of p53+/- (and wild type) mice exposed for 4, 13, or 26 weeks to 2 mg/kg melphalan (MLP), a chemotherapeutic agent with carcinogenic potential. In addition, telomere length was evaluated in bone marrow cells by quantitative fluorescence in situ hybridization (Q-FISH). Chromosome aberrations were significantly increased in both tissues after MLP treatment. The p53 genotype did not influence the response of spleen cells, whereas a slight but significant increase of the aberration frequency was measured in the bone marrow of p53+/- mice exposed to MLP for 13 weeks with respect to the level detected in the matched wild-type group. The main finding of our still preliminary results on telomere length modulation was again a difference between the two genotypes. In bone marrow cells of wild-type mice, MLP treatment was associated with telomere shortening, while in p53+/- mice telomere elongation was the prevalent response to MLP exposure. In agreement with previous literature data, our in vivo study suggests that even the lack of a single functional copy of the p53 gene might have an impact on the quantity and quality of chromosome alterations induced in cycling cells by a clastogenic exposure.     

Induction of cytogenetic damage in rodents after short-term inhalation of benzene

Experiments were designed to investigate both the induction of sister chromatid exchanges (SCEs) in peripheral blood lymphocytes (PBLs) and micronuclei (MN) in bone marrow polychromatic erythrocytes (PCEs) of mice and rats after inhalation of benzene (BZ). Male DBA/2 mice (17-19 weeks old) were exposed to target concentrations of either 0, 10, 100, or 1,000 ppm BZ for 6 hr. Male Sprague-Dawley rats (11-14 weeks old) were exposed to target concentrations of either 0, 0.1, 0.3, 1, 3, 10, or 30 ppm BZ for 6 hr. Blood was obtained by cardiac puncture 18 hr after exposure, and PBLs were cultured in the presence of lipopolysaccharide (mouse B cells, 60 micrograms/ml) or concanavalin A (rat T cells, 30 micrograms/ml) to stimulate blastogenesis for SCE analysis. Femoral bone marrow smears from both species were analyzed for MN in PCEs 18 hr after BZ exposure. Mouse PBLs revealed a significant concentration-related increase in the SCE frequency over controls at 10, 100, or 1,000 ppm BZ. Mouse bone marrow showed a significant concentration-dependent increase in MN over controls after exposure to 10, 100, or 1,000 ppm BZ. Rat PBLs showed a significant increase in the SCE frequency after exposure to 3, 10, or 30 ppm BZ. The statistical significance of the 1 ppm BZ result was borderline and dependent on the statistical test chosen. Rat cells revealed a significant concentration-related increase in MN after inhalation of either 1, 3, 10, or 30 ppm BZ. PBLs from treated mice showed significant concentration-dependent decreases in mitotic indices; however, cell cycle kinetics and leucocyte counts remained unaffected. Rat PBLs showed significant decreases in mitotic activity only after exposure to 3 and 30 ppm BZ, whereas cell cycle kinetics and leucocyte counts were unaffected. These results show that BZ can induce statistically significant cytogenetic effects in PBLs and PCEs of both mice and rats after a 6-hr inhalation of BZ at low concentrations.     

The role of RIP1 and RIP3 in the development of aplastic anemia induced by cyclophosphamide and busulphan in mice

This study aimed to investigate the role of RIP1 and RIP3 in the pathogenesis of aplastic anemia (AA) induced by cyclophosphamide and busulphan in mice. Animals were randomly divided into three groups: the control group, the AA group, and the Nec-1 group. Mouse AA model was established by intraperitoneal injection of cyclophosphamide (40 mg/kg/d) and busulfan (20 mg/kg/d) for 12 days. The Nec-1 group mice received intraperitoneal injection of Nec-1 (2 mg/kg/d) for 12 days prior to intraperitoneal injection of cyclophosphamide (40 mg/kg/d) and busulfan (20 mg/kg/d) for 12 days. The control mice received intraperitoneal injection of equal volume of saline. At 12 h after the last intraperitoneal injection, blood and bone marrow tissues were collected from mice. Peripheral blood cells were analyzed using hematology analyzer and the histological changes of bone marrow tissues were examined using scanning electron microscopy (SEM). The levels of RIP3 and RIP3 in bone marrow were measured using Western blot analysis and the interaction of RIP1 and RIP3 proteins was investigated on the basis of immunoprecipitation analysis. ELISA was used to measure the levels of IL-6, TNF-α, and FLT-3L in bone marrow tissue supernatant. Apoptosis and necrosis of bone marrow cells were analyzed using flow cytometry. Western blot showed that the expression of RIP1 and RIP3 was significantly increases in AA mice compared to the normal controls. Immunoprecipitation detected the pro-necrotic RIP1-RIP3 complex, suggesting that RIP1 and RIP3 mediated necroptosis may involved in the damage of bone marrow cells. Compared to the AA mice, Nec-1 group mice exhibited significantly increase of peripheral blood cells and mononuclear cells in bone marrow tissues and decrease of the apoptosis/necrosis of bone marrow cells. In addition, we observed significant decrease of IL-6, TNF-α, and FLT-3L in bone marrow tissue supernatant in the Nec-1 group mice compared to AA mice. Our results suggest that Nec-1 can prevent the development of AA by inhibiting bone marrow cells necrosis and the production of inflammatory mediators. RIP1 and RIP3-mediated necroptosis may involve in the pathogenesis of AA induced by cyclophosphamide and busulfan in mice.     

Cytogenetic damage induced in vivo to mice by single exposure to cesium chloride

Female laboratory bred albino mice (2n = 40) were orally administered cesium chloride (CsCl) in aqueous solution as a single dose and the damage induced at the chromosomal level was observed in bone marrow cells after 6, 12, 18, and 24 hours of exposure. The concentrations of the chemical given were calculated as fractions of the LD50, namely 1/5, 1/10, and 1/20. The cytogenetic endpoints screened for were chromosomal aberrations (CA) and divisional frequency or mitotic index (MI). The frequency of chromosomal aberrations induced was directly proportional to the concentration of the chemical administered. The highest dose was the most toxic and was considered to be the maximum tolerance level. Effects on divisional frequency were variable, the highest concentration being significantly mitostatic, the middle one ineffective, and the lowest slightly mitogenic. In general, the observations indicate that CsCl is clastogenic when administered orally to mice in vivo and the effects are dose-dependent.     

Haemopoietic growth factors significantly improve the mitotic index and chromosome quality in cytogenetic cultures of myeloid neoplasia

Haemopoietic growth factors stimulate bone marrow cell division, differentiation, and survival in vivo. We have investigated the use of recombinant human haemopoietic growth factors in vitro to improve cytogenetic cultures. Using a combination of granulocyte colony stimulating factor, granulocyte macrophage colony stimulating factor, stem cell factor, and interleukin-3, we developed an additive for bone marrow cultures intended to stimulate myeloid cell growth. Sixty-seven paired parallel cultures were analyzed, of which 50 were abnormal. The growth factor (GF) cultures showed a median four- to five-fold increase in mitotic index (MI) (P < 0.0001). In addition, the chromosome morphology was significantly improved in the GF cultures with a median increase in United Kingdom National External Quality Assessment Scheme quality score of 1.25 points (P < 0.0001). There was no statistically significant difference in the number of abnormal cells between the two culture methods. The combination of higher MI and improved chromosome quality substantially reduces the time required to process a case; furthermore, the GF medium is cheaper than the medium with which it was compared. This method is suitable for both diagnostic and follow-up cytogenetic analysis of acute and chronic myeloid neoplasia and is particularly useful for poorly cellular marrow samples or blood samples that would be expected to fail on standard culture. The use of this method has enabled substantial improvements in work efficiency in our oncology cytogenetic laboratory and reduced average reporting times from 9.0 days (2004/5) to 7.1 days (2005/6), despite a 6% increase in sample numbers.     

Antimutagenic activity of afobazole in various regimens of treatment

The influence of a new 2-mercaptobenzimidazole derivative afobazole on cytogenetic effects of dioxidine and cyclophosphamide was studied by counting chromosome aberrations in bone marrow cells of C57B1/6 mice. Afobazole (1–100 mg/kg perorally) exhibited antimutagenic activity determined by its antioxidant properties. This activity depended on the dose and treatment shedule. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 130, No. 11, pp. 539–542, November, 2000     

Modification of clastogenicity of three known clastogens by garlic extract in mice in vivo

The anticlastogenic activity of crude extract of garlic (Allium sativum L.) was studied in bone marrow cells of mice. Male laboratory-bred Swiss albino mice were given one of three concentrations of the freshly prepared extract (100 mg, 50 mg, and 25 mg/kg body weight) as a dietary supplement by gavage for 6 consecutive days. On the seventh day the mice were administered a single acute dose of two known clastogens, mitomycin C(1.5 mg/kg) and cyclophosphamide (25 mg/kg) or sodium arsenite (2.5 mg/kg), simultaneously with garlic extract. After 24 hr, chromosome preparations were made from the bone marrow cells. The endpoint studied were chromosomal aberrations and damaged cells. Garlic extract alone induced a low level of chromosomal damage. The clastogenicity of all three mutagens were reduced significantly in the animals which had been given garlic extract as dietary supplement. The extent of reduction was different for the three clastogens and may be attributed to the interaction with the different components of the extract. © 1993 Wiley-Liss, Inc.     

Effect of AC II, an herbal formulation in cyclophosphamide-induced immunosuppression in BALB/c mice--Implication in HIV treatment

Effect of AC II, herbal drug formulation in reducing immunosuppression caused by administration of cyclophosphamide was studied. Mice were injected cyclophosphamide (CTX) 50 mg/kg b.wt. for 14 days with or without the drug and total WBC, bone marrow cellularity and alpha-esterase positive cells were determined. On day 15, total WBC count in cyclophosphamide treated mice was 1500 +/- 420 cells/mm3, while in AC II-treated mice it was 7658 +/- 376 cells/mm3. On day 16, administration of cyclophosphamide reduced bone marrow cellularity to 3.42 +/- 0.38 x 10(6) cells/femur from the normal value of 13.83 +/- 0.96 x 10(6) cells/femur. In AC II treated group bone marrow cellularity was increased to 8.05 +/- 0.7 x 10(6) cells/femur. The number of alpha-esterase positive cells was found to be reduced to 177 +/- 25 cells per 4000 cells in CTX treated groups. But in AC II-treated group the number of alpha-esterase positive cells were raised to 843 +/- 86 cells per 4000 cells, which was closer to that of normal (710 +/- 49 cells per 4000 cells). Results indicate the usefulness of AC II to combat immunosuppression induced by chemical and biological agents.     

Stimulation of Hematopoiesis in Untreated and Cyclophosphamide Treated Mice by the Inhibition of Prostaglandin Synthesis

Indomethacin (IN) was administered to untreated or to cyclophosphamide (CY) treated C57B1/6 mice to study the roles of prostaglandins in regulating hematopoiesis. The following hematopoietic parameters were quantitated: 1) peripheral blood leukocyte (PBL) count; 2) total nucleated cells per spleen; 3) total nucleated cells per femur; and 4) spleen weight. Assays were performed in vitro to measure the number of colony forming units (CFU) present in the bone marrow and spleen. Untreated mice administered IN had a transient rise in their PBL count. These animals also developed splenomegaly and had an increased number of nucleated cells in their spleen. All CY treated mice had a marked decrease in PBL count, spleen cellularity, bone marrow cellularity, and spleen size during the first 5 days after CY treatment. These observations were followed by hematopoietic recovery over the next 10 days. Cyclophosphamide treated mice exhibited a more rapid hematopoietic recovery when treated with IN than without IN treatment. Analysis of the CFU capacity of bone marrow and spleen cells in soft agar showed a larger number of CFU in the bone marrow and spleen of IN treated mice or of CY/IN treated mice than in animals not receiving IN. These results indicate that prostaglandins are involved in the regulation of hematopoiesis in untreated mice and that prostaglandins may limit the hematopoietic recovery of CY treated mice.