Rats And Humans And The Carcinogenic Effects Of Brence
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6.4. Rats and mice
Rats have been used extensively for decades as a model for human mycotoxicoses especially with regard to the carcinogenic potential of AF. This model system, however, has been a subject for debate due to the differences in the detoxification mechanisms between rats and humans as shown by cytosolic conjugation of AFB1 in vitro (Raney et al., 1992). In contrast to rats, mice are generally resistant to the hepatocarcinogenic effects of AFB1. This may explain the high level of glutathione-S-transferase (GST) activity in mice challenged with AFB1 (Quinn et al., 1990). Contrary to the hepatocellular carcinomas commonly found in rat studies with AFB1, mice given AFB1 by intraperitoneal injection at 0.02 mg/kg of body weight…show more content… In a 155-day feeding trial, AFB1 (600 lg/kg) was shown to depress feed efficiency and rate of gain in steers. Decreased feed efficiency in cattle has been attributed to compromised ruminal function by reducing cellulose digestion, volatile fatty acid (i.e. acetate, propionate, and butyrate) production and rumen motility (Diekman and Green, 1992). Several mechanisms of bovine immunosuppression by AFB1 have been illustrated in vitro; (Sharma, 1993) demonstrated that AFB1 suppressed mitogen-induced stimulation of peripheral lymphocytes. In another study (Bodine et al., 1984), AFB1 was shown to inhibit bovine lymphocyte blastogenesis. Ochratoxins, on the other hand, do not cause significant toxicity to cattle when fed alone in naturally occurring doses. Barley naturally-contaminated with OTA (390–540 lg/kg) and low levels of AFB1 (12–13 lg/kg) did not induce any significant clinical symptoms in 12-week-old calves. T-2 toxin is also believed to induce immunosuppression in cattle by decreasing serum concentrations of IgM, IgG, and IgA, neutrophil functions and lymphocyte blastogenesis, and the response of lymphocytes to phytohemagglutinin (Cantiello et al., 2007). This toxin was also shown to induce necrosis of lymphoid tissues. Bovine infertility and abortion in the final trimester of gestation also have resulted from consumption of feed contaminated with T-2 toxin (Placinta et al., 1999).