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air. Therefore, we have examined the stability of the racemic all-trans isomer of fecapentaene-12. Into DMSO solutions of the compound pure oxygen was introduced and the decomposition was monitored by the Ames assay with strain TA100 and by UV spectroscopy. After 10 min of continuous oxygenation, mutagenicity as well as UV absorption decreased to about half of the original value. After 25 min of exposure to oxygen 80% of the compound were deteriorated and 375 revertants/plate were induced by the remaining 20% of the compound. These findings reveal that fecapentaenes are ultimate mutagens which do not need further activation by oxygen to obtain their mutagenic potency. In contrast, when samples were exposed for 8 h to air, no significant changes in mutagenicity could be observed. Therefore, DMSO solutions of the racemic all-trans isomer of feca- pentaene-12 are remarkably stable. For that rea- son, we trust that this compound should be used for investigating the carcinogenicity for feca- pentaenes in animals to classify its role in the etiology of colon cancer.

79 De Flora, S., C. Bennicelli, A. Camoirano, P. Zanacchi, M. Bagnasco, A. Picciotto 1 and V. Savarino 1, Institute of Hygiene and 1 Chair of Gastroenterology, University of Genoa, Genoa (Italy)

Circadian course of gastric juice mutagenicity and of its ability to inhibit mutagens

The circadian monitoring of intragastric pH and of the mutagenicity of 440 gastric juice sam- ples collected hourly from 22 subjects showed a weak yet consistent increase in his + S. typhimurium revertants during the 3-4-h periods following each meal, irrespective of diagnosis and treatment. Such mutagenic activity was not related to the histidine content of gastric juice, was due to thermostable components and was not significantly inhibited by administration of vitamin C. Mixed genetic mech- anisms were involved, differing from those conse- quent to enrichment of gastric juice with high amounts of nitrite. Administration of an antiulcer drug (famotidine) at dinner or at bedtime was

followed by a nocturnal plateau of mutagenicity. However, such effect was not due to mutagenicity of the drug or of its derivatives, but to the ther- apeutic rise in pH associated with its antisecretory activity.

In vitro, ascorbic acid prevented the formation of mutagenic derivatives resulting from the reac- tion, in acidic environment, between nitrite and histamine H2-receptor antagonists, i.e. cimetidine, ranitidine and famotidine. Natural (glutathione) or synthetic (N-acetylcysteine) thiols also reduced the mutagenicity of nitrite-drug mixtures, mainly by blocking the mutagenic derivatives rather than by inhibiting the nitrosation reaction. Neverthe- less, thiols were also effective in decreasing nitrite mutagenicity.

While gastric juice did not affect the mutagen- icity of some direct-acting mutagens (e.g. nitrite, ICR 191, folpet, nitrofurantoin) or promutagens (e.g. aflatoxin B 1 and benzo[a]pyrene), it stabi- lized or enhanced the mutagenicity of other com- pounds (e.g. MNNG, ICR 170, captan) or, on the contrary, decreased the mutagenicity, e.g. in the case of sodium azide (inactivated with pH-related mechanism) and of Cr(VI) compounds. Chro- mium reduction was due to thermostable compo- nents of gastric secretion and was favoured by the acidity of the gastric environment. The circadian monitoring of this phenomenon in several individ- uals showed a basal activity during interdigestive periods (less than 10/~g Cr(VI) reduced per ml of gastric juice), an peaks (tens of ~g/ml) during the 3-4-h periods after each meal.

(This study was supported by Italian CNR (Special Project "Oncology").)

8O Ziegler-Skylakakis, K., and U. Andrae, Institut ffir Toxikologie, GSF, Neuherberg/Munich (F.R.G.)

Genotoxicity of nitropropane in mammalian cells in vitro and in vivo

2-Nitropropane (2-NP) is a widely used in- dustrial solvent. Prolonged inhalation of 2-NP causes hepatocellular carcinomas in male and, less efficiently, female rats. The mechanism by which the compound acts as a carcinogen is unclear. It has been suggested that 2-NP is a direct (metabo-

lism-independent) initiator or that tumours may be initiated by nitrosamines formed from endoge- nous amines and nitrite produced by hepatic de- nitrification of 2-NP. Others have claimed carcinogenicity to be due to a non-genotoxic mechanism since toxic doses of the compound cause massive cell damage and subsequent cell proliferation. In the present study, we have ex- amined whether 2-NP is genotoxic and mutagenic in mammalian cells or not and compared its ef- fects to those of its isomer, 1-nitropropane (1-NP). Whether 1-NP is carcinogenic or not is not known. Genotoxicity was assessed by monitoring DNA repair synthesis in cultured rat hepatocytes (HPC) or mammalian cell lines treated with 1-NP and 2-NP in vitro and in HPC derived from rats i.p. injected with 1-NP or 2-NP and sacrificed 4 h later. In vitro, both isomers (0.1-10 mM) clearly induced DNA repair in the HPC, 2-NP being considerably more effective than 1-NP. Whereas 1-NP was similarly genotoxic in HPC from male and female rats, 2-NP induced more repair synthe- sis in HPC from female than from male rats. In contrast, when 2-NP (20-80 mg/kg) was adminis- tered in vivo, male rats were much more suscepti- ble to repair induction than female rats. 1-NP was ineffective in inducing DNA repair in vivo both in males and in females. Neither 1-NP nor 2-NP induced repair in V79 cells or several other cell lines of extrahepatic origin. However, in V79 cells both 1-NP and 2-NP caused concentration-depen- dent, quantitatively similar, increases in the frequency of thioguanine-resistant mutants in the absence of an added external metabolic activation system.

The results suggest that the genotoxicity of 2-NP, detected as induction of DNA repair in the liver in vitro and in vivo, reflects the tumour-ini- tiating activity of the compound in rat liver. The mutagenicity of 1-NP and 2-NP in V79 cells ap- pears to be due to a different mechanism causing gene mutations but not DNA damage subject to excision repair and may be unrelated to carcino- genicity.

81 Kugler-Steigmeier, M.E., U. Friederich, U. Graf, P. Maier and Ch. Schlatter, Institute of Toxicol-

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ogy, Swiss Federal Institute of Technology and University of Zurich, Schwerzenbach (Switzer- land)

Testing of 2,4,5- and 2,4,6-trimethylaniline in the Salmonella assay, in mammalian cell cultures, and in Drosophila melanogaster and comparison of the results with carcinogenicity data

In the standard Salmonella mammalian micro- some assay (Ames test) 2,4,5-trimethylaniline is positive after in vitro activation with rat liver $9, whereas the structurally related 2,4,6-trimethyl- aniline remains negative. This latter result does not correspond with the in vivo long-term assays in mammals where both compounds are carcino- genic. A possible reason for this might be an inadequate metabolic activation in the in vitro mutagenicity test. We intended therefore to test both compounds (1) in the Salmonella assay with different amounts of $9, (2) in Drosophila melanogaster (somatic mutation and recombina- tion test), and (3) in mammalian cell cultures (granuloma pouch assay). With increasing amounts of rat liver $9 (Aroclor 1254 induced), 2,4,6-tri- methylaniline became positive in the Salmonella assay, though it never reached the mutagenicity of 2,4,5-trimethylaniline. Both in Drosophila and in cell cultures 2,4,6-trimethylaniline was weakly but significantly positive at doses 2-3-fold lower than those necessary to induce similar effects with 2,4,5-trimethylaniline. These results agree with those of the long-term carcinogenicity assays where 2,4,6-trimethylaniline is carcinogenic at lower do- ses than 2,4,5-trimethylaniline. It is therefore con- cluded that 2,4,6-trimethylaniline is slightly more genotoxic than 2,4,5-trimethylaniline.

82 Sommer, E.W., H. Pech and G. Zbinden, Institut ftir Toxikologie, ETH und Universit~tt Ziirich, CH-8603 Schwerzenbach (Switzerland)

An in vivo/ in vitro assay for chemically trans- formed rat fibroblasts

A rapidly proliferating subcutaneous granula- tion tissue of 30-day-old, male Sprague-Dawley