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ditional factors, that is, toxic dust with its constant ingredients - - curing accelerators. Some of them are mutagenically active which is revealed through the experiment with blood and embryonic tissue cultures.

10 Antoshchina, M.M., and N.V. Luchnik, Institute of Medical Radiology, Academy of Medical Scien- ces, Obninsk (U.S.S.R.)

Estimation of mutagenic activity using the record of sister-chromatid exchanges (SCE) and chro- mosomal aberration (CA)

The high resolving power of SCE scoring as well as the relative simplicity of technique involved when compared with the study of CA forced many authors to use SCE instead of CA as a test for mutagenic activity. The purpose of our study was to analyse the changes of response of different stages of mitotic cycle to irradiation for various types of chromosome structural changes. Chinese hamster cells synchronized in G 1 stages were in- cubated in a medium with 5-bromodeoxyuridine, irradiated with 1 Gy of 6°Co 7-rays, and fixed at varying time intervals after irradiation. The slides were handled using the technique of sister-chro- matid differentiation. The sequence of mitoses, frequency of SCE and CA were studied in metaphase cells. The results obtained may be sum- marized as follows.

(1) The greatest yield of CA was observed when irradiated during G 2 stage. The frequency of CA was significantly higher in the cells of the first cycle, although the analyses of CA in M 1 and M 2 cells were performed during the same time after irradiation in the first postradiation mitosis. (2) The greatest frequency of SCE was observed when irradiated during S stage. Side by side with SCE some 'sister-subchromatid exchanges' (SsCE) were observed involving only a fraction of chromatid cross-section and affecting small segments of chro- mosome. The dependence of frequency upon the cell cycle stage was the same of SCE and SsCE; we concluded therefore that SsCE were in fact the

small intercalary SCE. (3) In the late replicating (heterochromatin) segments we have observed a number of isolabelled segments (IL). The distribu- tion of IL among the heterochromatic segments was random. Their frequency was increased after irradiation.

The above-mentioned results as well as some published data about regularities of production of SCE and CA show that there is no reason for replacement of CA for SCE when estimating mutagenic acvitity.

11 Arni, P., Ciba-Geigy Ltd., Basle (Switzerland)

Studies of the influence of chemicals on mutagen- induced recombination in yeast

Induced recombination or mutation may be inhibited or promoted by the action of particular chemicals. The blockade of D N A repair pathways by these chemicals is supposed to be the reason.

The influence on recombination was investi- gated with stationary and growing cultures of Sac- charomyces cereoisiae strains D7 and MP-1 after treatment with caffeine, chloroquine and Tween 80. These substances are known for their DNA-re- pair inhibiting properties in bacterial as well as in mammalian cells. Furthermore, compounds were tested which inhibit DNA synthesis or enzyme activities. 4-Nitroquinol ine-N-oxide, acridine orange or UV-light were used as inducers of re- combination processes. Simultaneous treatment of growing cultures of strain D7 with 4-nitroquino- line-N-oxide or acridine orange and Tween 80 resulted in a reduction of gene conversions. Treat- ment with caffeine, chloroquine or with Tween 80 after previous irradiation with UV-light did not change the number of gene conversions. Stationary cultures of strains D7 or MP-1 were not influenced by treatment with caffeine, chloroquine or Tween 80. Simultaneous treatment of growing cultures of strain D7 with a mutagen and Tween 80 resulted in most cases in an increase in the number of colony-forming units in comparison with cultures treated with the mutagen alone. Chloroquine and

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caffeine, however, revealed a slight growth in- hibiting effect at higher concentrations.

The effect of the compounds tested on induced recombination in yeast were generally weak. The effects observed with Tween 80 could partially be explained by an interaction of the substance with the mutagen used. The findings indicate, that the influence on recombination in yeast may not ex- clusively be the result of a direct blockade of repair processes.

12 Barafiski, B., B. Jaros-Kamifiska, B. Przybojewska and E. Spiechowicz, Institute of Occupational Health, Lodz (Poland)

Mutagenicity of some dyes used in industry

The aim of the study was the evaluation of mutagenic and genotoxic properties of two dyes belonging to triarylmethane derivatives: Acid Blue 7 (C.I.42080) and Acid Green 16 (C.I.44025).

The dyes were tested in the Ames Salmonella/ microsome plate assay, the DNA alkaline elution assay in rats, the micronucleus test and the domi- nant lethal assay in mice. The effect of both dyes on the DNA melting and remelting temperatures in vitro conditions was assessed. Negative and positive controls were included in all experiments.

Acid Blue 7 and Acid Green 16 were mutagenic in the Salmonella typhimurium strains TA1538 and TA98 when tested in the presence of a rat-liver metabolic activation system: no mutagenicity was observed in the absence of activation. Acid Blue 7 was mutagenic at doses of 100-1000 #g/p la te , Acid Green 16 at 500-5000 /~g/plate. In the micronucleus test Acid Blue 7 and Acid Green 16 induced significant increase in polychromatic erythrocytes with micronuclei when administered intraperitoneally at doses of 38-600 mg/kg and 75-1200 mg/kg, respectively.

In the dominant lethal assay Adic Blue 7 and Acid Green 16 were administered to male mice in a single intraperitoneal injection at doses of 220 mg/kg and 360 mg/kg, respectively. Acid Blue 7 induced a slight increase of postimplantation losses in females mated from day 25 to day 28 after

treatment. Acid Green 16 did not show the muta- genic activity in this test.

In in vitro systems none of the dyes without $9 mix induced changes in the melting and remelting curves of DNA from calf thymus.

In the DNA alkaline elution assays in rats the single, intraperitoneal administration of Acid Blue 7 at doses of 200 mg/kg and 350 mg/kg or of Acid Green 16 at doses 445 mg/kg and 780 mg/kg did not result in a dose-dependent increase in DNA single-strand breaks.

The tested dyes are indirect mutagens, active in in vitro and in vivo systems.

13 Bhrta, I., M. Ad~mkovh*, K. Proke~ **, D. Markarjan *** and F. Adzigitov ***, Medical Fa- culty of Hygiene, Charles University, Prague (Czechoslovakia), * Institute of Experimental Medicine, Czechoslovak Academy of Sciences, Prague (Czechoslovakia), ** Oncological Labora- tory, Faculty of Medicine, Charles University, Prague (Czechoslovakia), *** Institute of Experi- mental Pathology and Therapy, Academy of Medical Sciences, Sukhumi (U.S.S.R.)

The long persisting aberrations induced by aflato- xin B 1 in mammals. Mathematical modeling

Chromosome aberrations were scored in bone marrow, cells of Cricetulus griseus hamster and Macaca mulatta monkeys given a single i.p. injec- tion of aflatoxin B 1 (AFB 1). The mutagenic activ- ity of AFB 1 was assessed by the percentage of cells bearing aberrations and by the total frequency of chromosome and chromatid breaks. Chinese ham- sters were treated with 5 different doses of AFB 1 ranging from 1 #g to 5 mg/kg (LDs0/30 = 12.2 mg/kg) and the aberration yields at each AFB 1 dose level tested were determined at 24-h intervals

"for 5 consecutive days. Compared to controls the increase in the two types chromosome abnormali- ties was significant in all tests. At 5 mg/kg of AFB 1 the tests were carried out over a period of 92 days to assure the analysis of aberration yields with time. All chromosome aberration assays con- ducted during this period showed significant in-