S76 Abstracts / Toxicology Letters 189S (2009) S57–S273 (M K-HS) solution, at 37 ◦ C. The reaction of GI muscle strips to acetylcholine (ACh) applied in the optimal concentrations (which were stated in former experiments as 1 M for stomach fun- dus and jejunum and 10 M for stomach corpus) was studied. The data obtained in this study indicate, that the response of jejunum strips to ACh treatment differed throughout the whole incubation period. The preparations reacted always with signifi- cant contraction. However, the strength of the response altered depended on the incubation duration. It suggests low time-stability of jejunum strips’ model during long-term experiment. In contrast, the force of stomach corpus and fundus smooth muscle reaction to ACh application stabilized after the first hour of incubation and maintained unchanged during following hours of experi- ments. doi:10.1016/j.toxlet.2009.06.227 V37 The response of gastrointestinal smooth muscle strips to differ- ent reference substances may dependent on the preparation’s origin Natalia Dziekan, Magdalena Chlopecka, Marta Mendel ∗ , Maria Wiechetek Warsaw University of Life Sciences, Department of Preclinical Sciences, Division of Pharmacology and Toxicology, Warsaw, Poland The development of new techniques and the ethic considerations demands inventing novel models that can be alternative to the clas- sical experiments performed on life animal. An alternative model that could be used for this purpose is isolated gastrointestinal (GI) strips. However, there is no single in vitro model designed to study motor activity of the gastrointestinal tract that would be carefully standardized or validated. One of the most important stages of the standardization process is defining the reference sub- stance and estimating their optimal concentrations. Therefore, we aimed to evaluate the reaction of rat isolated GI strips on vari- ous concentrations of acetylcholine (ACh) and isoproterenol (Isop) and nominate their optimal concentration. The experiments were performed on rat isolated stomach strips in isotonic conditions dur- ing an incubation in modified Krebs–Henseleit solution (M K-HS), at 37 ◦ C. After the equilibration period, increasing concentration of ACh or Isop was applied cumulatively. Acetylcholine induced a concentration-dependent contraction of each investigated mus- cle strip. For stomach fundus a clear dependence was observed in concentration range from 0.01 M to 100 M and for stom- ach corpus from 0.1 M to 1000 M. Relaxant dose-dependent response of stomach muscle to isoproterenol was observed in con- centration range from 0.001 M to 10 M for stomach fundus and from 0.01 M to 10 M for stomach corpus. Thus, the opti- mal concentration recommended to use as a control of muscle contractile or relaxant ability may vary depending on the prepa- ration’s origin and amounts: (a) for the stomach fundus 1 M (ACh and Izop), (b) for gastric corpus 10 M (ACh) and 1 M (Izop). doi:10.1016/j.toxlet.2009.06.228 V38 Comparative cytotoxicity effect of zearalenone and its metabo- lites on the CHO-K1 cells Guillermina Font ∗ , Cristina Juan, Monica Fernandez, Houda Berrada, Maria Jose Ruiz Universitat de Valencia, Medicina Preventiva, Burjassot Valencia, Spain Zearalenone (ZEA) is a non-steroidal estrogenic mycotoxin pro- duced by several species of fungus Fusarium. It is widely found in maize, barley, wheat, oats, sorghum and sesame seeds, as well as in hay and corn silage, which are prime ingredients in many food prod- ucts for humans or animals. ZEA can be transformed to at least five different metabolites including zearalanone, a- and b-zearalenol and a- and b-zearalanol. Its metabolites cause reproductive tract disorders and impaired fertility due to their estrogenic activity. On the other hand, it has been suggested that the reduction of ZEA to a- and b-zearalenols occurs mostly in the liver. In this study, the cytotoxicity effect of ZEA and its metabolites in the CHO-K1 cell line was investigated. In order to carry this out, the influence of these derivatives on cell viability using the neutral red cell viabil- ity assay, was tested. The effect of entero-hepatic circulation in the metabolism of ZEA was also tested by adding the cytochrome solu- tion P450 1A1 (CYP1A1) to cell cultures exposed to ZEA and the generation of ZEA-metabolites, was also tested. The concentration of ZEA and its metabolites, before and after the CYP1A1 exposure on the CHO-K1 cell line was analyzed with a liquid chromatography- tandem mass spectrometer (LC/MS/MS). The results demonstrated that ZEA and its metabolites reduce cellular viability in CHO-K1 cells in the following increasing order: a-metabolites Acknowledgement: This work was supported by the Spanish Sci- ence and Education Ministry (AGL2007-61493). doi:10.1016/j.toxlet.2009.06.229 V39 Effect of rhamnocytrine-4 ′ -beta-d-galactopyranoside, isolated from Astragalus hamosus L., in combination with cyclophos- phamide on cell viability in freshly isolated rat hepatocytes Magdalena Kondeva-Burdina 1,∗ , Mitka Mitcheva 1 , Ilina Krasteva 2 , Stefan Nikolov 2 1 Faculty of Pharmacy Medical University Sofia, Pharmacology, Pharmacotherapy and Toxicology, Sofia, Bulgaria, 2 Faculty of Pharmacy Medical University Sofia, Pharmacognosy and Botany, Sofia, Bulgaria Cyclophosphamide is a classical alkylating agent used for the treat- ment of chronic lymphocytic leukemia, malignant lymphomas, Hodgkin’s disease, early-stage primary breast cancer, small-cell lung cancer, etc. In this study we investigated the effects of rhamnocytrine- 4 ′ -beta-d-galactopyranoside, isolated from Astragalus hamosus L., administered alone (in concentrations 10 M and 100 M) and in combination with cyclophosphamide (in concentration 60 M) on freshly isolated rat hepatocytes. Rhamnocytrine-4 ′ -beta-d-galactopyranoside is a new flavonoid, isolated from Astragalus hamosus L. Rat hepatocytes were isolated by two-stepped collagenase per- fusion. The cell viability (by trypan blue method) was measured as sign of cytotoxicity.