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When mouse liver microsomes were preincubated at 37 degrees with buffer, the monooxygenase activity was nearly constant and lipid peroxidation very low over 15 min. When preincubated with NADPH, there was an increase in lipid peroxidation accompanied by loss in enzyme activity (about 40%). The addition of EDTA 5 or 40 mM depressed lipid peroxidation and protected the monooxygenase activity with a rate increasing with concentration. The addition of FeSO4 0.5 mM had only little effect one enzyme activity whereas stimulated the response of the 2-thiobarbituric acid test.

During measurements of radioactivity in some milk samples with liquid scintillation counter (about one year after the nuclear accident of Chernobyl) we have observed an increase of the values of scintillation fluid with the passing of time. Although this enhancement is absolutely small (about 2 c.p.m. in 500 min), it is very important for an exact measurement of samples at low counting, as those tested. Our protocol of measure provides for insertion of alternate blanks and samples in the automatic sample-holders of liquid scintillation counter. The values of measurement of samples are taken during the increase phase subtracting the value of blank interpolated on the increasing straight line from c.p.m. of sample. Finally, we report the collected values of the whole radioactivity in some milk samples: at least 5-6 nCi/L contrary to about 1 nCi/L of 137Cs reported by USL. In our opinion it is important to consider the whole radioactivity as measure of the overall biological danger of radioactive samples. In fact, this measurement takes into account also biologically very dangerous radionuclides as 3H, 14C, 90Sr.

1,2-dichloroethylene cis and trans were tested for their ability to induce point mutation, mitotic gene conversion and mitotic recombination in a diploid strain (D7) of the yeast Saccharomyces cerevisiae in a suspension test with and without a mammalian microsomal activation system. In this test 1,2-DCE cis and trans were toxic but not genetically active even with S9 activation.

Usual "in vitro" mutagenesis tests combine microbial test systems with mammalian metabolism (microsomal assay). Some cases are known in which expected positive results are not obtained due to many factors operating between the microsomes in the incubation mixtures and the nucleus of the test microbial cells (detoxifying mechanisms, permeability effects, unstable intermediate, alternative targets in the pathway, etc.). In these cases, useful additional information could be obtained using microbial test systems with incorporated metabolism. Microbial systems and in particular yeasts in Cytochrome P-450 dependent metabolizing activity are known since many years. We studied under this aspect the strain D7 of Saccharomyces cerevisiae, used in our laboratory, in order to standardize the conditions for optimal metabolizing activity. The composition of the culture medium, the growth phase, and the effect of the amount of the initial inoculum, were studied. Cytochrome P-450 content was determined by the technique of difference spectra (reduced cytochrome +/- CO). Results on the effect of glucose and sodium phenobarbital concentration in the culture medium were in agreement with the literature. Moreover we found that the cytochrome P-450 contents was markedly dependent on the size of the initial inoculum, being higher and the smaller was the initial inoculum.

Mutagenicity study "in vivo" (Intravenous host mediated assay) confirms suspension test results with cis- and trans -1,2-dichloroethylene: no genetic effects could be detected. Single and repeated doses of trans-1,2-DCE induced liver aminopyrine demethylase and cytochrome P-450 whereas the cis- isomer decreased them. Similar results were obtained after induction with phenobarbital + beta-Naphthoflavone.

Aminopyrine-N-demethylase, p-nitroanisole-O-demethylase and lipid peroxidation were determined in liver postmitochondrial fractions (S-9) of mice in the basal state and after induction with beta-naphtoflavone, sodium phenobarbital, or both the inducers. The two activities were similar in their response to all inductions: meanly, 1,2 times with beta-NF, 2,0 times with Na-PB, 5,8 times with Na-PB+ beta-NF. Lipid peroxidation was sensibly more active in basal animals with respect to that with induction. The results are discussed in a partial review of the sector literature, which deserves still much work to be completed.