[Radiosensitivity of a thymocyte subpopulation capable of stimulating erythropoiesis in locally irradiated animals]

It was shown that, in contrast to intact thymocytes and to those irradiated with a dose of 0.25 Gy, thymocytes exposed in vivo to doses from 0.5 to 1.5 Gy and transplanted to locally irradiated (7 Gy) thymectomized BALB/c mice failed to stimulate the recovery of the erythron.

[Mechanisms of T-lymphocyte stimulation of erythropoiesis under local body irradiation]

Thymocytes transplanted into thymectomized mice with a locally irradiated lower limb in a dose of 7 Gy were accumulated in the depleted bone marrow to stimulate the processes of postradiation erythron regeneration. Cytosar treatment did not affect the regulatory function of thymocytes. At the same time thymocytes treated with actinomycin D possessed less powerful stimulating effect than intact ones.

The elevation of blood levels of zinc protoporphyrin in mice following whole body irradiation

Elevation of zinc protoporphyrin (ZPP) levels in the blood has served as an indicator of lead poisoning and iron deficiency anemia for many years. We have discovered that sublethal doses of whole body irradiation with x-rays also elevates ZPP 2-3-fold over normal levels. The ZPP level does not begin to increase until days 12-14 postirradiation and peaks between days 18 and 20 before returning to normal levels between days 28 and 35. Increasing the radiation dose delays the onset of the rise in ZPP, but does not affect the magnitude of the elevation. At lethal doses, ZPP elevation is not observed. Neither of the two previously described mechanisms that cause elevations of ZPP, namely iron deficiency and inhibition of ferrochelatase, are responsible for the radiation-induced elevation of ZPP. The elevation of ZPP appears to be correlated with the recovery of the hematopoietic system from radiation injury.

A cellular analysis of residual hemopoietic deficiencies in mice after 4 repeated doses of 4.5 Gray X rays

A sub-optimal plateau in numbers of femoral stem-cells (CFU-S) in mice after 4 doses of 4.5 Gray X rays (each separated by 21 days), was shown to persist at 20-30% of control up to 1 year after the last dose, when about 50% of the mice had survived. The concentration of white cells in the blood was maintained persistently at about 70% of control, whereas the concentration of red cells was normal up to 4 months and then it declined to about 75% of control at 10 months after irradiation. Concentrations of some committed progenitor cells in the marrow (GM-CFC and ERC), which are capable of amplification cell divisions, were intermediate between the concentrations of marrow stem cells and mature blood cells in both the granuloid and the erythroid cell lineages, respectively. Hence increased amplification was a mechanism operating for a prolonged period in the production of numbers of mature cells. The numbers were subnormal, however, and this corresponded to only 1 extra amplification division on average. There was a slow decline after 6 months in the numbers of CFU-S, BFU-E and GM-CFC, and in the hematocrit, with reference to age-matched controls. The decline was due partly to a prevention of the natural increase in cell numbers in the marrow with the age of the mice, which was also seen with the femoral content of a stromal progenitor cell (CFU-F). A defect in the repeatedly-irradiated CFU-S population was detected as a persistent inability to produce colonies containing the same number of daughter CFU-S as contained in colonies derived from unirradiated marrow and assayed at the same time.

The effects of low dose (less than 1 rad) X-rays on the erythropoietic marrow

Adult female Sprague-Dawley rats were exposed (200 kvp X-rays) to whole body doses of 22-1320 mrad and examined for changes in the level of red blood cell precursors (RBCp) in the marrow at 5-30 weeks post-irradiation, under nonbled and phlebotomy-induced anemic stress conditions. Increases in the RBCp %, RBCp/mg marrow, and RBCp/skeleton under nonbled conditions, and a suppressed erythroid response to an induced anemia, were found after acute doses in the range of at least 70 mrad. Dosages of 22 or 44 mrad that induced no measurable changes when applied only once were found to be effective when they were employed 4 or 2 times/week, respectively. The results suggested the presence of a linear-quadratic dose-response relationship in which the quadratic function exists between 88 and 981 mrad, and the linear dependency, below 88 mrad.

[State of erythrocytes after long-term exposure to magnetic field]

During and after exposure to a constant magnetic field of 1.6 T mice, showed variations in the size distribution of red blood cells, with their shape remaining unchanged and enlarged cells being predominant. This shift persisted till exposure day 10 and began to return to normal on days 15, 22 and 30. After irradiation the Price-Jones curve varied in a different manner and recovered by day 6. The changes in the curve were not correlated with variations in the reticulocyte and erythrocyte counts or hemoglobin content. It is concluded that an exposure to a constant magnetic field produces insignificant lesions in the red blood cell membrane. Mention should be made of a reduction of the reticulocyte count in the peripheral blood after exposure.

The distribution of the haeme and non-haeme fractions of iron in individual regions of the erythropoietic system of intact and acutely irradiated mice

In male mice of the strain C57BL/10ScSnPh, both intact and X-irradiated with a whole-body sublethal dose, the distribution of the content of total and haeme iron was studied in individual bones, the spleen, liver, plasma and erythrocytes, using an original mineralization and extraction technique. In the erythropoietic organs as a whole and in the individual bones the haeme and non-haeme iron compartments were distinguished, and within these the iron accounted for by circulating plasma and by erythrocytes and erythrocyte precursors. In the radiation-depleted marrow there were quantitative and qualitative changes in the compartments, particularly the creation of an important compartment of non-circulating (fixed) erythrocytes.

[Stimulation of postradiation regeneration of erythropoiesis in mice with Bordetells pertussis vaccine]

Inoculation into mice of killed B. pertussis vaccine (10(10) microbial cells) one day before their sublethal irradiation (6.0 Gy) was accompanied by accelerated regeneration of erythropoiesis in the bone marrow, particularly in the spleen as was judged by the 59Fe incorporation. B. pertussis also induced an increase in endocolonization when inoculated 4-5 days after irradiation. The latter suggests a possible effect of vaccine on the hematopoietic cells, less differentiated than erythropoietin-sensitive cells (ESC), inasmuch the sensitivity of the ESC to erythropoietin commonly appeared at the later stages. When B. pertussis was inoculated into BALB/c mice one day before their infection by Rauscher's leukemia virus noticeable activation of leukemogenicity was observed. It is believed that the reason for this is the stimulation of erythroid target cells for the virus after B. pertussis vaccination. The data obtained indicate that B. pertussis vaccine activates erythropoiesis in both normal and irradiated mice.

Susceptibility to merocyanine 540-mediated photosensitization: a differentiation marker on murine hematopoietic progenitor cells

Merocyanine 540 (MC 540) is an impermeant fluorescent dye that binds preferentially to fluidlike domains of the cell membrane. Photoexcitation of membrane-bound dye causes a breakdown of the normal permeability properties of the membrane and, eventually, cell death. We have used in vitro and in vivo clonal assays to determine the relative sensitivities of different classes of normal murine hematopoietic progenitor cells to MC 540-mediated photosensitization. Late erythroid progenitors (CFU-E) were the most sensitive cells, followed in order of decreasing sensitivity by early erythroid progenitors (BFU-E), megakaryocyte progenitors (CFU-Meg), day 7-spleen colony forming cells (day 7-CFU-S), granulocyte/macrophage progenitors (CFU-GM), and day 11-spleen colony forming cells (day 11-CFU-S). Bipotent progenitors of the granulocyte/macrophage lineage were more sensitive than unipotent macrophage progenitors but less sensitive than unipotent granulocyte progenitors. Progenitors giving rise to large granulocyte/macrophage colonies were more sensitive than progenitors giving rise to small colonies ("clusters"). We conclude that sensitivity to MC 540-mediated photosensitization is develop-mentally regulated and that differences occur even between the most closely related classes of progenitor cells. Our findings indicate the usefulness of MC 540 as a plasma membrane probe. They also support the contention that early and late-appearing spleen colonies are the progeny of two distinct classes of progenitor cells.

[Mechanism of erythropoietic regeneration in local irradiation of the bone marrow]

In experiments on BALB/c mice it was shown that in conditions of local irradiation (7.0 Gy) of one hind foot there was an appreciable accumulation of T-lymphocytes in the exposed bone marrow which stimulated the erythroid cell proliferation and, as the result, accelerated the post-irradiation regeneration of erythropoiesis.

Induction of micronuclei in the mouse. Revised timing of the final stage of erythropoiesis

The early effects of X-rays, vincristine, cyclophosphamide, quinacrine dihydrochloride, cycloheximide, actinomycin D and hydroxyurea on the induction of micronuclei in mouse bone-marrow erythrocytes were studied. A significant increase in the incidence of micronuclei in polychromatic erythrocytes was seen as early as 5 h after a single treatment with vincristine, 6 h after treatment with X-rays and 10 h after treatment with cyclophosphamide. The cell kinetics of the mouse erythropoietic system described by Cole et al. (1981) can be modified to fit these results. According to this revised model, the final mitosis takes place only 5 h before the expulsion of the nucleus.

Kinetic studies of radiation damage and recovery of murine haemopoietic stem cells during and after continuous irradiation at low dose rate

Under continuous gamma irradiation at a low dose rate of 0.70 Gy/day, the cellularities of blood forming cells in bone marrow decrease with increasing accumulated radiation dose. The biphasic nature of the dose-response curve may be due to the following factors: an increased rate of proliferation of CFUs, different radiation sensitivities of CFUs, GM-CFC and E-CFC, an increase in the amplification potential of progenitor cells and proliferative haemopoietic cells, and a reduction in differentiation 'pressure' on CFUs. After 49 days of chronic irradiation the content of E-CFC in murine bone marrow recovers rapidly, and approaches the pre-irradiation level by 5 days. However, the number of CFUs and GM-CFC reaches a plateau value of only 40% of normal within 34 days.

Effect of 131I on the anemia of hyperthyroidism

Data from the National Thyrotoxicosis Therapy Follow-Up Study (NTTFS) are presented here to document the existence of anemia in hyperthyroidism, a mild and reversible anemia that is simultaneously ameliorated with reversal of the hyperthyroid state. Among 20,600 women entered into the NTTF study with no previous history of hematological disorders, the prevalence of anemia was found to range from 10-15%, appearing to be higher in those selected for treatment with 131I when compared to those selected for surgery. An attempt is made to verify the recent hypothesis that thyroid hormone levels in the supraphysiologic range may suppress erythrogenesis. Two statistically significant regression models are consistent with a hypothesis of thyrotoxic bone marrow suppression. However, both associations are weak enough to suggest that some other physiologic improvement underlies the amelioration of anemia when hyperthyroidism is reversed. The degree of improvement in hematological status is similar for women in both treatment groups. Among 4464 women for whom serial hematological tests are obtained, over 3/4 of anemic patients are no longer anemic after an average 6.2 yr of follow-up. Clinicians are reassured that radioactive iodine exposure causes no further insult to the bone marrow, no matter what the cumulative dosage. The highly fractionated low dose bone marrow exposures to radiation account for the minimal hematological risks of 131I treatment.

Factors affecting haemoglobin synthesis in the mouse

The effect of various forms of haematopoietic stress on haemoglobin production was studied in mice. During acute anaemia, recovery from polycythaemia or irradiation, there was an increase in the number of reticulocytes, and this was associated with a marked increase in the total protein synthesis. The specific activity in reticulocytes increased up to 20-fold from the normal. The maximum specific activity usually preceded the maximum peak of reticulocytosis. The proportion of minor haemoglobin increased by up to 30%, and there was a significant correlation between the specific activity in reticulocytes and the proportion of minor haemoglobin synthesized. These results indicate that erythropoietic stress results in the release of a new population of reticulocytes that are very active in protein synthesis as measured by markedly increased specific activity, and that this coincides with an increase in the proportion of minor haemoglobin produced.

Erythropoietic effect of ultraviolet radiation in blind rats in comparison with control seeing rats

In 40 blinded rats erythropoiesis parameters were determined in four groups of 10 animals each and were compared with similar parameters in seeing control rats. Two group of blind rats received ultraviolet radiation 405-289 nm wavelength; 140 000 erg/sec/cm2 daily for 10 minutes during 2 or 4 weeks. Two other groups served as non-irradiated blind controls. The determined parameters showed the following rise (+) or fall (-) in per cent in relation to the non-irradiated rats: haematocrit (H) +3.6 and 9.3; erythrocyte count (E) +15.1 and 13.2; reticulocyte count (R) +65.5 and 184.1; haemoglobin level (Hb) +6.6 and 13.1; 59Fe incorporation index into erythrocytes (EFe) +27.3 and 30.4, into spleen (SFe) +35.8 and 34.3, into liver (LFe) -20.9 and -19.3, into bone marrow (BFe) -22.8 and -41.9. In the seeing animals all these parameters were significantly greater; H +11.4 and 7.9; E +56.9 and 26.6; R +288.9 and 199.1; Hb +22.3 and 5.1; EFe +64.1 and 42.5; SFe +195.8 and 134.7; LFe -35.4 and -29.9; BFe -65.2 and -57.2.

Erythropoietin formation during hypoxia in mice with impaired responsiveness to erythropoietin induced by irradiation or 5-fluorouracil injection

Plasma erythropoietin levels during continuous exposure to hypobaric hypoxia in mice with marrow aplasia induced by whole body X-irradiation of 5-fluorouracil injection were higher than in control mice similarly exposed. There findings give support to the hypothesis that a relationship exists between erythropoietin production rate and erythroid responsiveness to the hormone.

A solution to the controversy on stem cell regulation

Supplementary to the discussion in Blood Cells 7 (1981) pp. 417-443 concerning regulatory mechanisms of stem cell proliferation and differentiation, the consequences of the two proposed hypotheses of Blackett and Botnick and Lord have been calculated. It can be shown that their equations are equivalent and can be transformed into each other. However, their verbally described regulatory mechanisms are different and turn out to be more important than the equations. The assumptions of Blackett and Botnick lead to an unstable behaviour of the stem cell system with cyclic cell numbers while the hypothesis of Lord leads to stable recovery curves.

Purification of erythroblastic nests

We describe a method for preparing purified erythroblastic nests in large numbers (approximately 10(6)/run) in three steps: (1) induction of splenic erythropoiesis in mice, (2) preparative differential centrifugation for the removal of erythrocytes and single cells from spleen cell suspensions, and (3) sedimentation in an isokinetic gradient of Ficoll 400 in Joklik's modification of minimum essential medium. Viability of isolated EN is very high, as demonstrated by the trypan blue exclusion and in vitro erythrocyte formation methods.

Cyclic erythropoiesis in W/Wv mice following a single small dose of 89Sr

Young adult female W/Wv mice were given 0.5 microCi 89Sr/g intravenously, a dose which produces no anemia and only mild transient thrombocytopenia in normal mice. In the W/Wv animals platelet counts fell from 10(6) to 3 x 10(5)/mm3, and hematocrits from 39% to 25% in two weeks. In the following 2 weeks, platelet counts rose to 7 x 10(5), stabilizing at this level. Average hematocrit values were observed to oscillate from a nadir of 26% to a zenith of 42%, with a periodicity of about 16 days. In a repeat experiment we found the average hematocrit fluctuation from 28 to 40%, amplitude of reticulocyte fluctuation 6 to 31%, periodicity of cycle 16 days. Several animals have been observed through as many as six complete cycles. Further study of cyclical erythropoiesis in the W/Wv mouse following hematopoietic injury produced by 89Sr may shed light on the causes of cyclical hematopoiesis observed occasionally in man and other animals.

The effect of chloramphenicol on erythropoiesis in X-irradiated mice

Mice irradiated with a dose of 4,78 Gy X-radiation were treated 3 or 5 days with a thrice-daily dose of chloramphenicol of 160 or 320 mg/kg. Observation of the incorporation of 59Fe into the heme fraction suggested that chloramphenicol has a depressive effect on erythropoiesis in the spleen of nonirradiated animals, and clearly proved this in irradiated ones. Depression in the bone marrow of nonirradiated animals was not observed, in irradiated animals a depressive effect was shown, though less strong than in the spleen. As benefits these findings there is an accentuation of postirradiational anemia after chloramphenicol treatment of irradiated animals, and signs of incipient anemia in nonirradiated animals. All the effects mentioned were repaired within 14 days of the end of chloramphenicol treatment.

Effect of zinc on protoporphyrin induced photohaemolysis

Zinc is readily inserted into protoporphyrin suspended either in a salt-sucrose buffered solution or endogenously present in red cell haemolysate in erythropoietic protoporphyria. Red cells from healthy persons were incubated with metal-free protoporphyrin or zinc-protoporphyrin and irradiated with light at 360-470 nm. The photohaemolysis was significantly less with zinc-protoporphyrin compared with that of the metal-free protoporphyrin. The results are discusssed in relation to the possibility of using zinc as a photoprotective and hepatoprotective agent in erythropoietic protoporphyria.

Response of hepatic hematopoiesis to whole body irradiation

Extensive hepatic erythropoiesis, granulocytopoiesis and megakaryocytopoiesis occur in adult mice given methylcellulose (MC). This appears to be a compensatory response to MC induced hemolytic anemia and thrombocytopenia. The present study was undertaken to evaluate the effects of whole body irradiation (WBI) upon established hepatic hematopoiesis (HH) as well as its effect when given before the induction of HH. Established hepatic erythroid and granulocytic foci were significantly decreased 24 hours after 100 or 300 rads. The DO for erythroid and granulocytic foci was 107 +/- 10 rads and 95 +/- 20 rads respectively, similar to those reported for murine marrow and spleen cell CFUS. Megakaryocytes were more radioresistant, gradually declining over 7 days to 50% of control values following 100 rads and with a DO of 347 +/- 7 rads; suggesting a differential radiation sensitivity compared to erythroid and granulocytic foci. WBI, 100 and 300 rads, given before MC failed to prevent subsequent development of HH although both marrow and spleen responses were reduced. Hepatic granulocytic foci and marrow peroxidase positive cells were reduced by such treatment while erythroid and megakaryocytic foci were similar to controls. This suggests that irradiation damaged stem cells responded to MC with increased erythropoiesis and megakaryocytopoiesis at the expense of granulopoiesis.

Iron incorporation after single and fractionated irradiation of infant mice

The erythropoiesis in control and irradiated infant mice was investigated on the basis of incorporation of iron into hemopoietic organs and blood. Iron incorporation in bone marrow increased from the second week of life reflecting the maturation of the marrow whereas that in the spleen showed only minor changes. Irradiation of infant mice on day 6 or 9 caused a bone marrow syndrome characterized by an impaired iron incorporation into hemopoietic tissues and blood, by a reduced utilization of serum iron, and particularly by a delayed maturation of the erythropoietic functions of bone marrow. Fractionated irradiation not only had a greater effect on mortality but also caused a more severe and long lasting depression of erythropoiesis than a single dose.

Haematological studies on 90Sr-90Y-toxicity. I. Ferrokinetic changes in peripheral blood of mice

Erythropoietic changes were observed, measured by 59Fe-uptake into red blood cells, and on radioiron turnover from blood plasma, at different time intervals (2--64 days) after treating adult female mice with varying activities of 90Sr-90Y. Activities of 2.5 or 5.0 mu Ci radiostrontium per animal lead to a depression at time intervals of two and four days, at longer periods there was an overshoot. With activities of 0.5 or 1.0 mu Ci radiostrontium disturbances in the radioiron uptake are still observed, although these effects are not as pronounced as in experiments with higher burdens. In comparison with results obtained in experiments in which the plasma 59Fe-turnover was applied, even with an activity of 5 mu Ci radiostrontium per mouse, no deviation as against the untreated controls was detected.

Human erythropoiesis in diffusion chambers

The diffusion chamber technique has been modified in order to stimulate human erythropoiesis in addition to granulo- and monocytopoiesis. The chamber recipient mice were subjected to a combination of 750 rad irradiation and long-term non-interrupted hypoxia (0.5 atm) without chamber retransplantation. 7 d after implantation erythroid cells started to increase, reaching a maximum of up to 70% of the nucleated cells on day 12.

Effect of bleeding on irradiation-induced erythropoiesis in the spleen of AKR mice

The effect of erythropoietin, increased by bleeding, on the erythropoiesis induced by irradiation in the spleen of AKR mice, has been studied. The following parameters were measured to quantify the erythropoietic activity: the number and size of hematopoietic nodules (colonies) and proerythroblasts in the spleen, the spleen, blood and red-cell 59Fe uptake and the hematocrit and reticulocytes in the blood. Under erythropoietic stimulus an increase in the number and size of colonies was observed and these colonies were observed sooner because of their more rapid growth. The proerythroblasts in the spleen appeared earlier, and there were increases in the spleen, blood and red-cell 59Fe uptake and in the hematocrit and reticulocytes in the blood.

Relevance of specific activity in experimental erythrocytocide by 55Fe

Iron loads between 0.20 microgram and 26 microgram, added to 5 mu Ci 59Fe, were followed for up to 150 days in mice. Relative organ uptake increased as a function of iron load in liver and kidneys while it decreased in bone marrow and blood. Several weeks after injection, all load-related differences disappeared.

Suppression of mouse erythroid colony formation by L1210 leukemia cells

The effect of L1210 transplantable leukemic cells on in vitro formation of erythroid colonies from CD2F1 mouse bone marrow progenitor cells (CFU-E) was investigated. Clonal cell culture was carried out by a methylcellulose technique. Human urinary erythropoietin served as the stimulator. After 44 hours of incubation aggregates of eight or more erythroid cells were scored as colonies. The number of CFU-E which could be demonstrated in marrow cells from mice that had been injected intravenously 6 days before with 5 x 10(4) L1210 cells was far below that obtained from normal marrow cells. When 1.3 x 10(5) marrow cells from leukemic mice or L1210 ascites cells were cultured with an equal amount of normal cells, the number of CFU-E expressed was reduced by 51% and by 86%, respectively, relative to controls with normal cells only. Neither lethally irradiated L1210 cells (4500 rad) nor L1210 cell conditioned media suppressed erythroid colony formation. It is suggested that in L1210 leukemia erythropoiesis is decreased because of a cell-to-cell inhibitory action of the leukemia cells on CFU-E.

The recovery of iron uptake in erythropoietic bone marrow following large field radiotherapy

Large X-ray fields, such as those used to irradiate major lymph-node areas in the treatment of lymphomas, often irradiate large areas of haemopoietic bone marrow. The absorbed doses received by the marrow are close to the tolerance level. Quantitative scanning of the bone marrow, using 52Fe and a digital whole-body scanner, has been carried out in a series of 22 patients treated by radiotherapy up to nine years previously in order to assess the extent and recovery of their erythropoietic marrow. The results showed large variations from patient to patient; in some patients the iron uptake in the marrow returned to near normal levels in two to three years, while in others the uptake remained suppressed after seven to eight years. The tolerance dose for the bone marrow appeared to be about 1100 ret. There was some evidence of a more rapid recovery of erythropoietic function in males than females, but no evidence to show that age of patient, type of disease or whether chemotherapy had been used influenced the results. Patients who showed a decreased iron uptake in an irradiated region of marrow generally showed a compensating increased uptake in unirradiated regions, which in some cases was associated with anaemia.

Effect of protein deprivation on hematopoietic stem cells and on peripheral blood counts

Experiments were performed to determined the effect of protein deprivation on CFU-S in the spleen and femoral marrow, on the peripheral blood counts, and on the rate at which these parameters regenerate following radiation. Splenic CFU-S decrease in number after only 3 days on diets containing 5% protein or less. Marrow CFU-S, on the other hand, decrease only after mice are fed a protein-free diet for 4 weeks or more. The hematocrits, platelet counts, and WBC counts fall in the latter group. Marrow CFU-S regenerate more slowly in irradiated mice fed diets containing 5% protein or less. Also, the hemocrits, WBC counts, and platelet counts of irradiated mice fed diets containing 5% protein regenerate more slowly than do those of irradiated mice fed normal diets. The effect of protein deprivation on erythropoietin production, erythropoiesis, granulocyte function, and immunocompetence is well known. The studies reported here indicate, in addition, that protein deprivation also causes the numbers of CFU-S and the platelet counts to decline.

Postirradiation erythropoietic recovery in splenectomized mice

The influence of splenectomy on erythropoietic recovery of lethally X-irradiated mice injected with different doses of syngeneic bone marrow was studied. Splenectomized animals showed less activation than unoperated controls in the lower dose range; however, by increasing the number of injected cells the response obtained was similar in both groups. Providing an adequate number of stem cells is administered to the splenectomized recipients, an enhanced erythropoietic activity of the graft may compensate for the absence of the spleen, which is an important organ in postirradiation recovery. Suggested explanations for this observation are lack of an haematopoietic inhibitory effect of the irradiated spleen, or changes in the environment provided by the spleenless host.

Changes in DNA associated with induction of erythroid differentiation by dimethyl sulfoxide in murine erythroleukemia cells

The Friend virus-infected murine erythroleukemia cell can be induced to differentiate along erythroid cells in culture with various compounds, including dimethyl sulfoxide. DNA from murine erythroleukemia cells cultured with dimethyl sulfoxide shows a decrease in sedimentation rate in alkaline sucrose gradients after alkali lysis of the cells. These changes can be detected as early as 27 hr after the beginning of culture. Similar results are observed with DNA of the cells cultured with other inducers, butyric acid and dimethylacetamide, but not with DNA from a variant cell line resistant to induction with dimethyl sulfoxide. Ultraviolet irradiation, which is known to cause similar changes in the sedimentation rate of DNA in alkaline sucrose gradients, induces differentiation of the murine erythroleukemia cells. These studies suggest that alterations in DNA may be related to events involved in the induction of differentiation of murine erythroleukemia cells by dimethyl sulfoxide.

Kinetics of erythropoiesis in the liver induced in adult mice by phenylhydrazine

Phenylhydrazine treatment of normal mice elicited a rise in the numbers of CFU-S in blood, spleen and liver. High numbers of CFU-S were found in blood and liver 4 d after the first phenylhydrazine injection. CFU-S in the liver decreased slowly and were absent after 2 weeks. Blood CFU-S returned to normal levels by day 6, whereas spleen CFU-S numbers remained high upto day 12 with a 20-fold increase being apparent between days 5 and 8. Bone marrow CFU-S numbers were relatively unaffected except for a dip between days 4 and 7 with a nadir at day 5 where numbers decreased to 50% of the control levels. Approximately 40% of liver, spleen and blood CFU-S present on the 4th d after initiation of phenylhydrazine treatment, were killed with a single dose of hydroxyurea whereas bone marrow CFU-S numbers were not significantly reduced by the drug. Splenectomy performed before (21 d) or during phenylhydrazine treatment did not diminish the number of CFU-S found in theliver on day 4. A 3 d interval was observed between peak numbers of CFS-U and erythroblasts in the liver which suggests that hepatic CFU-S are able to undergo differentiation along the erythroid pathway. The presence of maceophages was correlated with that of erythroblasts in the hepatic central veins. These macrophages may be essential to the liver environment for induction of erythropoiesis.

[Effect of erythrocyte breakdown products on mast cells and erythropoietin formation]

Experiments were conducted on CBA mice and albino rats. A study was made of the effect of erythrocyte destruction products (EDP) on the content of hemopoietic colony-forming units (CFU), differentiation of stem cells and the erythropoietin production. It was shown that 3 or 4 EDP injections to normal mice or to lethally irradiated (1000 rad) mice after the transplantation of bone marrow cells caused no changes in the CFU level of stem cells differentiation. In case of a daily (for 3 days) administration of EDP to mice before the irradiation (1000 rad) and bone marrow transplantation there was observed an increase of the colonies count in the recipients' spleen on account of the erythroid colonies. EDP injection caused no changes in the erythropoietic activity of the blood serum. A possible role of erythrocyte destruction products in the mechanism of erythropoiesis autoregulation is discussed.