Positive Control Experiment Research Articles

Development of tobacco smoke-induced lung tumors in mice fed Bowman-Birk protease inhibitor concentrate (BBIC)

Male strain A/J mice were exposed, 6h a day, 5 days a week for 5 months to a mixture of 89% cigarette sidestream and 11% cigarette mainstream smoke and then allowed to recover for another 4 months in air. The animals were fed Bowman-Birk protease inhibitor concentrate (BBIC) at a concentration of 1% in AIN-93G diet either during smoke exposure, following smoke exposure or during the entire 9 months. At the end of the experiment, the incidence and multiplicity of lung tumors were determined. In a positive control experiment, strain A/J mice were injected with 3-methylcholanthrene (MCA) and fed a diet containing 1% BBIC; these animals were killed 5 months later. It was found that in the animals treated with MCA, BBIC decreased lung tumor multiplicities, whereas in the smoke exposed mice, BBIC did not modulate lung tumor development.

Untargeted viral mutagenesis is not found in X-irradiated monkey cells.

The existence of untargeted viral mutagenesis in X-irradiated cells was investigated in a mammalian virus/cell system, where a low level of such viral mutagenesis can be demonstrated in UV-irradiated cells. In the positive control experiment UV-elicited mutagenesis was shown with cell exposures of 5, 10 and 15 J/m2 and a delay of 24 h between cell irradiation and infection with unirradiated herpes simplex virus. Although X-ray doses of 1, 3 and 10 Gy elicit enhanced reactivation of UV-irradiated virus, no untargeted mutagenesis for any X-ray dose at post-irradiation infection times of 0, 24 or 72 h was observed in this study. Thus untargeted mutagenesis of herpes simplex virus was not demonstrated in X-irradiated monkey cells, under conditions where X-ray-enhanced reactivation occurs and where untargeted mutagenesis in UV-irradiated cells occurs.

Germ cell studies in mice after prolonged exposure to nitrous oxide

Male and female Swiss Webster (SW) mice, age 13 to 14 weeks, were exposed by inhalation for 4 hr per day, 5 days per week, for 14 weeks, to either room air, 0.5% nitrous oxide, 5.0% nitrous oxide, or 50% nitrous oxide. Murine germ cells were examined for evidence of injury after this exposure. A group of male mice were treated with methyl methanesulfonate (MMS) as a positive control for sperm abnormalities while a group of female mice were treated with 3-methylcholanthrene (3-MC) as a positive control for oocyte destruction. There were no significant differences among the four inhalation exposure groups in testes weight, percentage of abnormally shaped sperm, sperm count, or histologic appearance of the testes; the mean percentage (±SE) of abnormal sperm ranged from 8.9 ± 2.4 (5.0% nitrous oxide) to 13.5 ± 0.5 (50% nitrous oxide) with a concurrent control value of 10.4 ± 2.3%. In the positive control experiment, 25.2 ± 4.1% of sperm from mice treated with MMS were abnormal compared with 2.5 ± 0.3% of sperm from mice treated with saline ( p < 0.001), indicating that sperm of SW mice are sensitive to chemical damage. There was no significant difference between the mean number of oocytes in mice treated with 50% nitrous oxide (33.3 ± 14.4) and in control mice (29.8 ± 8.0). In the positive control experiment, mice treated with 3-MC had significantly fewer ( p < 0.001) primordial oocytes, 67.2 ± 19.5 compared with control mice, 222.4 ± 21.9, indicating that this strain is sensitive to chemical damage of the ovary. Thus, murine germ cells showed no evidence of toxic effects due to prolonged exposure to nitrous oxide.