Mutagenic activity of metabolites contained in the plasma of Sprague-Dawley rats treated with cyclophosphamide.

In the present study we have tried to add some new results to those data previously obtained by Natarajan et al. (1983) and Darroudi and Natarajan (1985), where they have used in vivo metabolization and cytogenetic testing for in vitro analysis of xenobiotic compounds. Sprague-Dawley rats were treated intraperitoneally with 2.5, 5.0, 10.0 and 20.0 mg/kg b.w. of cyclophosphamide in order to obtain plasma containing active metabolites of the drug. The mutagenic activity was assessed by estimating the frequencies of sister-chromatid exchanges (SCE) in human and rat lymphocytes. No influence of animal age was observed on the metabolism of cyclophosphamide, which could be detected by SCE analysis. The increase in SCE frequencies in both human and rat lymphocytes was dependent on the doses applied. SCE frequencies are highly variable among individuals, showing statistically significant differences. The same effect, but to a lesser extent, was also found in rats. Rat lymphocytes can be assumed to be good biological material for chemical mutagenesis, as the animals can be maintained at almost constant experimental conditions. However, rat lymphocytes do not grow well in in vitro cultures. These data contribute to the preview proposal that combining metabolism in vivo and chromosome SCE analysis in vitro can be regarded as an important and very sensitive system to detect the mutagenic activity of low-dose exposure to chemical compounds requiring metabolic activation.

The effects of age, sex and diet on the clastogenic action of cyclophosphamide in mouse bone marrow.

7-week-old and 12-week-old mice of both sexes received either a control or protein-deficient diet for 3 weeks. Afterwards, they were given a single dose of cyclophosphamide (0.5 mg/10 g b.wt.) before being sacrificed. The relationship between age and the clastogenic action of cyclophosphamide can be observed in the bone marrow cells of male mice but not in those of female mice. 12-week-old males on a 75% protein-deficient diet have a lower frequency of cells with cyclophosphamide-induced chromosome aberrations than has the control group. On the contrary, 7-week-old males and females, and 12-week-old females, show that protein-deficient diets act synergistically with the clastogenic action of cyclophosphamide. These results are discussed taking the metabolism of the drug into account. Animal age also plays a role in the formation of chromosome rearrangements; this type of aberration is significantly more frequent in younger animals of both sexes than in older ones exposed to the drug.

Synergism between caffeine and gamma-radiation in the induction of dominant lethal mutations in oocytes and spermatozoa of Musca domestica.

Caffeine was studied with regard to its synergism with gamma-radiation in the induction of dominant lethal mutations in S14 oocytes and mature spermatozoa of M. domestica. In S14 oocytes an increase in the frequency of such a type of mutation was observed only when the exposure to gamma-radiation followed a pretreatment with a diet containing 0.2% of caffeine. Negative results were obtained with (a) post-treatment with the same kind of diet, (b) pretreatment with diets containing 0.1 and 0.02% of caffeine and (c) exposure to the radiation 6 h after interruption of the feeding treatment with the diet containing 0.2% of caffeine. Such influence of the conditions under which the treatment is performed and the synergistic effects is probably related to the food intake pattern and the rapid metabolism of the caffeine. When the 0.2% caffeine pretreatment was combined with an exposure of the oocytes to variable doses of gamma-radiation, the increments in the mutations observed seemed to be negatively correlated to the radiation doses used. Also, under such conditions, the dose/survival relationship fits well an exponential curve expressed by 1n y = -0.866x. With mature spermatozoa, synergism by caffeine was found only when the females, after having been mated with the irradiated males, were fed for 24 h on a diet supplemented with 0.2% of caffeine.

Radiation-induced dominant lethal mutations in oocytes of Musca domestica.

Dominant lethal mutations induced by gamma-radiation were measured in stage-7 and stage-14 oocytes of Musca domestica. At both stages the data are consistent with the multi-hit theory on radiation induction of dominant lethals. This conclusion is supported by fractionation experiments which indicate that both S7 and S14 oocytes are capable of repairing, in different periods of time, a similar amount of dominant lethal damage.